Vehicle noise at 160mhz

This forum is dedicated to helping people with questions about installing radio equipment in vehicles. This can include antenna installs, electrical wiring questions/problems, and mounting systems. Pictures of installs are welcome.

Note: Discussions regarding lighting, sirens, and other equipment now has its own forum in the 'off-topic' section below.

Moderator: Queue Moderator

Post Reply
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Vehicle noise at 160mhz

Post by Bill_G »

Need some thoughts on possible resolutions.

I've run into a 100 pennies problem with noise. One hundred pennies make a dollar. Rather than having a single source of noise, there are numerous sources in all the new commuter rail engines delivered by Colorado Rail last year. I've measured as little as 5db of rcvr desense in the railroad VHF radios mounted in the blunt end (rear) engineers cab, and as high as 25db at the aero end (front) radio. The blunt ends are always lower, but never higher than 6db desense. The aero ends are always higher, but never lower than 14db desense.

The radios are dash mount VHF CDM1550 to operate in the railroad band with Sinclair VHF "shark fin" transit antennas on the roof connected with 30ft of LMR200. Power is provided by a 70 to 12 converter dedicated to the radio that has zero measurable noise on the A+ line. Grounding looks excellent though it does depend on the welded steel unified body for the return at numerous bulkhead tabs where device / system ground cables attach behind fascades and service panels.

The conductors carry HT1250 packsets, and they have to step away from the trains at the platform to talk to dispatch. They can simplex to the engineer on their yard channel from one end to the other inside the passenger area, but neither of them can contact dispatch on the road channel with packsets or mobiles.

The spectrum analyser shows the antenna noise floor at -80db. Real time display shows numerous dynamic noise spikes through the band. Max hold accumulates quickly to -80db. The noise cloud is at the aero end where all the control devices are in the electrical closet. They're brand new engines with the latest and greatest rail control has to offer - a Windows based alarm and monitoring system; a cellular based Railcomm system with the latest GE cab signals and remote control; a DVR to record two interior and four exterior cameras for loss prevention; a wall of ip based PLCs; public wifi; the event recorder required by law; LED and flourescent interior lighting system. Turning off any one system rarely gains more than a couple db with the worst offenders being the CCTV surveillance system and the COMMS (ethernet switches, wifi, remote control) which contribute almost 4db each. As you systematically flip individual breakers off, the noise floor reduces. Turning it back on doesn't always immediately increase the noise because the devices may have to reboot / restart. Turning off everything takes the noise floor down to less than the spectrum analyser can measure, and rcvr desense drops to 2db out in the open yard.

The bottom line is no one system is causing The Noise. Almost all systems are contributing to the cloud. That's why I'm calling it a 100 penny problem. Short of rebuilding each cab, I have to come up with a solution. So far I have four ideas that the customer and my collegues have bounced around with varying degrees of acceptance. Let's see what you guys think.

(A) Move the antennas to the blunt end. Since the noise is greatly reduced towards the rear away from the cloud, mount both the aero and blunt antennas at the very rear of the cabs. Cable length for the aero radio will approach 100ft, but line loss at VHF is reasonably low, and a little attenuation may be our friend in this case.

(B) Remote control the blunt end radio from the aero end. Install a tone remote in the aero cab with a term panel on the rear radio. How the remote would mount would be a problem. Local control is not an option considering the noise. We want the common mode rejection a balanced line offers.

(C) Install a dual control head radio. The PM1500 has a dual head configuration with a 130ft cable option. While that would give us the greatest versatility for controlling the radio, we do not know how noise immune the cable is.

(D) Change the VHF CDM's to UHF and build a crossband repeater. They currently have one under-utilized UHF repeater channel with a comparator (12 UHF chans with 6 rcvr and 3 steerable xmitter sites returning by microwave to 12 comparators tied to an 9 position Gold Elite). Because they use existing heavy rail short lines for their service, they are required to be controlled and dispatched by the rail owner on RR VHF.

I've been asked to build a proof of concept for option A for one car.

We've gotten pricing for option C, but still working on the labor quote.

Nobody likes options B or D, though I think D is the real answer.

What do you think? Fresh eyes may come up with some better ideas.
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

It was brought to my attention by PM to be wary of LMR in mobile installations. Doing some searching on this board and teh google, I am convinced LMR is not the best choice for repeater operation despite industry reassurances. I have stories of my own bad experiences with LMR, but they have more to do with crimps failing than noise in the line. I can think of two in-building systems right now that use LMR400 and have mysterious intermittent noise problems. They might be worth a revisit.

Not that heliax is perfect. I have three chunks on my shelf of brand new LDF4-50 half inch with the center drifted out of the foam shorted against the corrugated wall - off the roll - bad from the factory. One was an indoor jumper and easy to find at the time. The others were on the tower and found with the Anritsu during acceptance, blamed on bad handling by the crew, but no evidence of kinking or construction damage. In all cases the center was against the wall, and the foam untorn perfectly filling the void.

But, I am grateful for the heads up. It made me rethink my proof of concept to move the antennas to the blunt. I was instructed to keep costs down and to use LMR400 for the test. I am reconsidering that now. I may do what I had originally desired: 85ft of half inch heliax across the roof attached to the HVAC shroud with a new drop of RG58 to the aero mobile, and a mag mnt on the blunt. I was warned by my engineers to avoid superflex because of torsional twist along the car body causing a failure in the cable. However, I am more concerned with transmit energy in the LMR cable causing outbound noise, and the vehicle noise cloud inducing inbound noise on the LMR. If my engineers are concerned about mechanical flexing of heliax and superflex, then they should be concerned with mechanical flexing of LMR which has been proven to cause noise. How embarrassing would it be to have a test solution be worse than the original problem?

This also makes me wonder about the choice of LMR200 in this application. There are transmit issues as well as receive issues in these installations which we were not part of. Most of the problems have been associated with connectorization workmanship on the LMR, loose connectors to the radios and antennas, failed power converters, under-sized converters, under-sized wire gauge to the converters, loose mounts, open ground crimps forcing return through the mounts, and loose bolts holding the Sinclair cleat to the roof. But, after all that work, there is still a problem with "lightning bolt" noise in transmit while the cars are moving, and I now suspect flexing LMR.

So again, I am grateful for the insight. You probably saved me at least one pair of dog bone underwear.
Jim202
Posts: 3609
Joined: Sun Sep 09, 2001 4:00 pm

Re: Vehicle noise at 160mhz

Post by Jim202 »

I am not a big fan of LMR coax cables for a number of reasons. Most of them are the foil and copper braid shields against each other. Not
a good bedfellow for two way radios.

As for your noise problems, I would have to say it is due to the noise being radiated from the computer interface cables. Most people don't
think about the signals and noise that these cables can generate. The use of shielded cables would mitigate the issue. However, there
are very few companies willing to take the effort and expense of using shielded interface cables on computer installations between
the computer and I/O equipment. The cabinets are fine, but there are always cables coming out of them and going places. Just
putting some ferrite snap on units probably won't help much.

As you found out, it is not one computer interface system causing the issue, but the whole pack of them. You might be able to get some
large old style coax like RG17 and strip the jacket off of it to get the large dia braid. Try slipping the braid over as many of the cables as
you can and ground just ONE end. With everything already installed, it may be hard to get the shield over all the different cable connectors.

If I had to be a betting person here, there was no effort to minimize any RFI that may have emitted from any of the electronics. It always
falls to the poor radio tech to patch up the design of the electrical engineer. He got paid the big buck to do a :o job. Now your stuck
making :o for pay and they expect you to walk on water.

My bet is there was nothing in the engine specs about radio interference in the design of this multi million dollar engine. If the company
had any brass ones, they would sent the engine back and tell the MFG to fix it. But we know that won't happen. Maybe rocking the
boat will get an engineer out to at least see the problem and then be told to resolve it. Don't hold your breath.

Jim



Bill_G wrote:It was brought to my attention by PM to be wary of LMR in mobile installations. Doing some searching on this board and teh google, I am convinced LMR is not the best choice for repeater operation despite industry reassurances. I have stories of my own bad experiences with LMR, but they have more to do with crimps failing than noise in the line. I can think of two in-building systems right now that use LMR400 and have mysterious intermittent noise problems. They might be worth a revisit.

Not that heliax is perfect. I have three chunks on my shelf of brand new LDF4-50 half inch with the center drifted out of the foam shorted against the corrugated wall - off the roll - bad from the factory. One was an indoor jumper and easy to find at the time. The others were on the tower and found with the Anritsu during acceptance, blamed on bad handling by the crew, but no evidence of kinking or construction damage. In all cases the center was against the wall, and the foam untorn perfectly filling the void.

But, I am grateful for the heads up. It made me rethink my proof of concept to move the antennas to the blunt. I was instructed to keep costs down and to use LMR400 for the test. I am reconsidering that now. I may do what I had originally desired: 85ft of half inch heliax across the roof attached to the HVAC shroud with a new drop of RG58 to the aero mobile, and a mag mnt on the blunt. I was warned by my engineers to avoid superflex because of torsional twist along the car body causing a failure in the cable. However, I am more concerned with transmit energy in the LMR cable causing outbound noise, and the vehicle noise cloud inducing inbound noise on the LMR. If my engineers are concerned about mechanical flexing of heliax and superflex, then they should be concerned with mechanical flexing of LMR which has been proven to cause noise. How embarrassing would it be to have a test solution be worse than the original problem?

This also makes me wonder about the choice of LMR200 in this application. There are transmit issues as well as receive issues in these installations which we were not part of. Most of the problems have been associated with connectorization workmanship on the LMR, loose connectors to the radios and antennas, failed power converters, under-sized converters, under-sized wire gauge to the converters, loose mounts, open ground crimps forcing return through the mounts, and loose bolts holding the Sinclair cleat to the roof. But, after all that work, there is still a problem with "lightning bolt" noise in transmit while the cars are moving, and I now suspect flexing LMR.

So again, I am grateful for the insight. You probably saved me at least one pair of dog bone underwear.
joescanner
Posts: 31
Joined: Fri Nov 30, 2001 4:00 pm

Re: Vehicle noise at 160mhz

Post by joescanner »

Jim202 wrote:If the company
had any brass ones, they would sent the engine back and tell the MFG to fix it. But we know that won't happen. Maybe rocking the
boat will get an engineer out to at least see the problem and then be told to resolve it. Don't hold your breath.
The MFG went out of business before this order was completed. That kind of guarantees that these DMUs won't go back. And good luck finding any of the original engineers.
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

Ha! Joe has obviously figured out who my customer is. Good job. Yes, Colorado Railcar is 10-7, never to return, with their assets purchased by US Rail with no commitment to support recent sales. There ain't no warranty on nothin. And rather than trying to fix the cars which is waaaaaay out of scope for my skill set, I'm going to take the cowards way out and find a way for their radios to work in the current environment even if it means using roip over their wireless internet connectivity to talk to dispatch. Think of it as the worlds most powerful bluetooth installation. All I need is a couple hundred bits to maintain a vpn, and 32kbps during a transmission. Won't be no big never mind. Might be fun to build.

That fits right in with the premise of option D - if you can't stand your neighbors, move out of the neighborhood. I may make it option (D).1.b RoIP with a low power simplex mobile, vpn appliance, and NXU in each car to give coverage on the train connected through the internet back to the service yard to a base station / NXU on the dispatch channel.
Jim202
Posts: 3609
Joined: Sun Sep 09, 2001 4:00 pm

Re: Vehicle noise at 160mhz

Post by Jim202 »

The only problem I see with your plan is trying to get system coverage over the entire rail line that it will cover.
Most of the VPN type service coverage I have had to deal with has troubles in even some cities. Let alone
way out in the puckerbrush that most of the rail lines go through.

One place you might want to go look at is SkyTerra and it's satellite service. Currently they have PTT dispatch
type service that works fairly well. Next year I think it is they are coming out with a new sat system that will
provide data as well. The only issue you will have to deal with is the long delays with the sat communications.
I have even used the RIOS gateway from Sytech Corp. through the SkyTerra system.

Jim


Bill_G wrote:Ha! Joe has obviously figured out who my customer is. Good job. Yes, Colorado Railcar is 10-7, never to return, with their assets purchased by US Rail with no commitment to support recent sales. There ain't no warranty on nothin. And rather than trying to fix the cars which is waaaaaay out of scope for my skill set, I'm going to take the cowards way out and find a way for their radios to work in the current environment even if it means using roip over their wireless internet connectivity to talk to dispatch. Think of it as the worlds most powerful bluetooth installation. All I need is a couple hundred bits to maintain a vpn, and 32kbps during a transmission. Won't be no big never mind. Might be fun to build.

That fits right in with the premise of option D - if you can't stand your neighbors, move out of the neighborhood. I may make it option (D).1.b RoIP with a low power simplex mobile, vpn appliance, and NXU in each car to give coverage on the train connected through the internet back to the service yard to a base station / NXU on the dispatch channel.
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

Mornin Jim - In this case it's a commuter rail deep in the heart of good cell coverage it's entire length. But, your warning to not depend on it is well taken. It sure would be fun to try though!

During CYA2K, when everybody was scrambleing for alternative phone and radio coverage, I must have put in a couple hundred American Mobile, GlobalStar, and Iridium sat phones. Those were some long days leading up to the blessed non-event. Some merely wanted dial tone into their phone system (additional CO's into the KSU). Some purchased PTT service. Some were stationary. Some were mobile. Some were portable. Amtrak purchased mobile with wierd baseball bat antennas that actually worked pretty good in the mountains and along the coast where nothing else existed previously for them. I think they still use it because of that. The delays caused all customers to do the Spock eyebrow trick. PTT call setup takes a long time, and audio is a bit bubbly at times. I was surprised at the accessories and innovations available. Kyocera's Iridium product line included a nest for four handsets on one antenna with a CO line card that met Bellcor standards. The phone companies loved it. American Mobile had tone remote controls for their Mitsubishi product allowing optimal RF placement when the control point was obscured. Some supported fax, some didn't.

On Jan 2 2000 most people tried to return the product. Uh, no. And we haven't seen much action since except for the occasional rental.
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

Update on the noise problem - finally received a new box of real Belden RG58 after our young and lovely office administrator thought perhaps I really wanted the "better stuff" instead of what I ordered. It was kind of her to be looking out for my and our customers best interests. I ran almost 90ft of it across the roof from a mag mnt with a quarter wave on the blunt end to the radio in the aero cab. Was very disappointed in the noise figure - 20db rcvr desense despite the long line making me wonder what drugs I'm on, and why I'm not sharing any. PLUS during the afternoon run the unit still had a bit of the "lightning bolt" xmit noise reporting a trespasser on the line well within the repeater coverage area. A supervisor on portable investigating the man came in loud and clear.

I am strongly suspicious of the aluminum louvers that hide the roof mounted HVAC and engine cooling system. They are merely riveted to bent pieces of metal bolted to aluminum angle bolted to a kindorf frame that is bolted to welded brackets. As I walked from one end to the other I noticed many of the louvers rattled when I thumped them. Not good. Hit them with enough energy and they will become noise makers just like rusty cyclone fencing around a site, and loose brass on a tower.

I am still awaiting the VHF on-glass antenna I ordered.
User avatar
Andy Corbin
Posts: 158
Joined: Tue Apr 19, 2005 3:46 pm

Re: Vehicle noise at 160mhz

Post by Andy Corbin »

Bill_G wrote:Update on the noise problem - finally received a new box of real Belden RG58 after our young and lovely office administrator thought perhaps I really wanted the "better stuff" instead of what I ordered. It was kind of her to be looking out for my and our customers best interests. I ran almost 90ft of it across the roof from a mag mnt with a quarter wave on the blunt end to the radio in the aero cab. Was very disappointed in the noise figure - 20db rcvr desense despite the long line making me wonder what drugs I'm on, and why I'm not sharing any. PLUS during the afternoon run the unit still had a bit of the "lightning bolt" xmit noise reporting a trespasser on the line well within the repeater coverage area. A supervisor on portable investigating the man came in loud and clear.

I am strongly suspicious of the aluminum louvers that hide the roof mounted HVAC and engine cooling system. They are merely riveted to bent pieces of metal bolted to aluminum angle bolted to a kindorf frame that is bolted to welded brackets. As I walked from one end to the other I noticed many of the louvers rattled when I thumped them. Not good. Hit them with enough energy and they will become noise makers just like rusty cyclone fencing around a site, and loose brass on a tower.

I am still awaiting the VHF on-glass antenna I ordered.
Hi Bill,
I have been following this thread with interest and have absolutely NO experience in dealing with railroad locomotives so I am trying to draw a mental picture of what you are dealing with. Sounds like you have your hands full.

I don't know if this is viable or not, if it would even work. Would it be possible to run solid copper pipe from the radio to the antenna feedpoint and snake the feedline through there. Just a thought.

Andy
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

Don't feel bad Andy. This problem is playing stump the chump, and winning. Yeah, running the line in a solid metal pipe might be the way to go. Even some emt might be appropriate. I pulled out a new CDM, programmed it, aligned it, thumped it, ran it on the paint shaker, ran it at 11v, etc, and then swapped it into the engine after the morning run. We'll see what happens. Last night there was a wind storm that knocked down a few trees and broke a few crossing arms meaning the trains had to read out a track procedure back to dispatch before moving (ala treating an intersection as a four way stop when the signal is out). Supervisors on portables at the crossings were L&C; this train was perfect standing still, broken up as he accelerated - just like before.

I'll check out the mobile I removed to see if something stupid is wrong that hasn't revealed itself in the cab like the antenna connector is spread just enough that the right wiggle in the wrong way causes it to cut out. I've seen that many times on Spectras.
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

Did you know that VHF on-glass antennas do not work on ballistic glass? Yeah, it's true. Absolutely no coupling between the inside and outside at all. Moving on to other ideas.

(a) build a vhf to uhf repeater for each engine so we can keep a vhf radio in the cab as required by regs. The uhf will link to a hilltop with another crossband rptr back to the dispatch channel. A desperate move, but will probably work.

(b) go high tech and build a vhf to NXU through the intertube link back to dispatch over the public free wi-fi on each train. Can you hear me now? Can you hear me now? Equally desperate, but way cooler.
Jim202
Posts: 3609
Joined: Sun Sep 09, 2001 4:00 pm

Re: Vehicle noise at 160mhz

Post by Jim202 »

I believe that the problem is due to the thickness of the window material. It's probably too thick for the coupling system of the 2 parts to perform correctly.

Jim



Bill_G wrote:Did you know that VHF on-glass antennas do not work on ballistic glass? Yeah, it's true. Absolutely no coupling between the inside and outside at all. Moving on to other ideas.

(a) build a vhf to uhf repeater for each engine so we can keep a vhf radio in the cab as required by regs. The uhf will link to a hilltop with another crossband rptr back to the dispatch channel. A desperate move, but will probably work.

(b) go high tech and build a vhf to NXU through the intertube link back to dispatch over the public free wi-fi on each train. Can you hear me now? Can you hear me now? Equally desperate, but way cooler.
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

Update with some success on the "lightning bolt" xmit problem - it was caused by narrowing the rptr rcvr bandwidth to 20kc using the NPSPAC setting in the MTR.

Early on I discovered severe desense on the rptr input from an adjacent channel user 30kc away and one hilltop over. The pass reject duplexer didn't have tight enough skirts to cut them out. I added a notch filter which helped. Setting the rcvr for NPSPAC also helped. Desense was down to slightly less than 10db. I ordered a crytal filter from Filtronetics which took care of the problem. However, I failed to restore the rcvr bandwidth setting back to 25kc. Low deviation users passed correctly. Loud user voice peaks noised up sounding like their antennas were failing, and we did find a lot of bad antennas in pursuit of this problem. Very interesting way for the rcvr to behave. Glad to have one issue put to bed.

Still no progress on the in-cab desense from other devices. I'm not holding out hope for resolving it in a mobile either.
KE7JFF
Posts: 270
Joined: Sun Nov 02, 2008 7:27 pm
What radios do you own?: MX300 lunchbox

Re: Vehicle noise at 160mhz

Post by KE7JFF »

You know, when I took a trip on the CRC DMU on the line you are talking about the first time, I remember taking my scanner along and noticed the conductors doing what you said; step out of the train and switch to the yard channel to talk to the cab. I thought the procedure was a bit too organized at each stop and I knew there had to be a more sensible reason.

I remember I was able to hear the road channel you speak of from inside the cab on my scanner (which has a lousy VHF frontend); can the conductors hear the road channel from inside or do they have no RX at all?

I know the basic operation of the CRC DMU, however, I am curious about the power sources for some of the systems you mentioned. Are they DC-DC converters or 120VAC inverters? Is the 802.11 hardware some off the shelf gear that plugs into the inverter? I would check those too. Also, I would try powering all those devices from an non-HEP power source at the yard with the train cold; it could be that the train's HEP is creating the field. I know it might be a basic troubleshooting step, but I always ask.

Though this is just a hunch; my only experience with installing radios in anything on the railroad was a MaxTrac in a caboose using a solar charged battery.
Mountain Wave Search & Rescue http://www.mwave.org
Support Search & Rescue: Get Lost!
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

I don't know if the electric power system qualifies as HEP or not. I'm not a locomotive expert. There is 70VDC distributed through each car to power accessories. At first the 12v dc/dc converters were mid-car in the main closet with small gauge wire run to each end to power the mobiles. They added a dc/dc converter in each console to power the radios locally which solved the voltage drop problem and allowed the CDM mobiles to transmit, but did nothing to address the rx noise. The conductors can sometimes hear the repeater on their portables in the passenger compartment depending on the location of the DMU on the line. But, portables become deaf in the aero end cab where all the control equipment is. As I wrote earlier, the steel shell body acts like a farraday cage and knocks rx levels down quite a bit even with everything turned off. Energize all the systems, and the noise floor comes up to -90db or higher. You have to be near a window to talk to dispatch on a portable. They work even better if you hold them out the window at arms length. The mobiles, despite having an antenna on the roof, are still affected by the cloud surrounding the entire car with 20db desense being normal. I have experimented with bringing in shore power to independent plain old power supplies to run the mobiles with no difference in the desense. I am pretty confident the dc/dc power sources are not the problem. It is everything else, and nothing can be turned off. And again, no one system contributes a majority of the noise. It is a one hundred pennies makes a dollar problem.

Those with institutional memory recall that light rail ran into similar issues trying to use the UHF system in the early days. Between the noise from the overhead power, and all the control systems aboard each train, the noise floor was significant enough to cause large coverage holes along the line. They escaped to the 800M analog trunking system to take advantage of the distributed, overlapping coverage offered by BOEC and WCCCA. The strategy worked, gave them complete end to end communications, and let them light up the tunnel with a standard BDA in the tunnel under the zoo. Unfortunately, the DMU's must stay on AAR channels to talk to Albany, and no one wants to entertain a crossband system.
KE7JFF
Posts: 270
Joined: Sun Nov 02, 2008 7:27 pm
What radios do you own?: MX300 lunchbox

Re: Vehicle noise at 160mhz

Post by KE7JFF »

Bill_G wrote:I don't know if the electric power system qualifies as HEP or not. I'm not a locomotive expert. There is 70VDC distributed through each car to power accessories. At first the 12v dc/dc converters were mid-car in the main closet with small gauge wire run to each end to power the mobiles. They added a dc/dc converter in each console to power the radios locally which solved the voltage drop problem and allowed the CDM mobiles to transmit, but did nothing to address the rx noise. The conductors can sometimes hear the repeater on their portables in the passenger compartment depending on the location of the DMU on the line. But, portables become deaf in the aero end cab where all the control equipment is. As I wrote earlier, the steel shell body acts like a farraday cage and knocks rx levels down quite a bit even with everything turned off. Energize all the systems, and the noise floor comes up to -90db or higher. You have to be near a window to talk to dispatch on a portable. They work even better if you hold them out the window at arms length. The mobiles, despite having an antenna on the roof, are still affected by the cloud surrounding the entire car with 20db desense being normal. I have experimented with bringing in shore power to independent plain old power supplies to run the mobiles with no difference in the desense. I am pretty confident the dc/dc power sources are not the problem. It is everything else, and nothing can be turned off. And again, no one system contributes a majority of the noise. It is a one hundred pennies makes a dollar problem.

Those with institutional memory recall that light rail ran into similar issues trying to use the UHF system in the early days. Between the noise from the overhead power, and all the control systems aboard each train, the noise floor was significant enough to cause large coverage holes along the line. They escaped to the 800M analog trunking system to take advantage of the distributed, overlapping coverage offered by BOEC and WCCCA. The strategy worked, gave them complete end to end communications, and let them light up the tunnel with a standard BDA in the tunnel under the zoo. Unfortunately, the DMU's must stay on AAR channels to talk to Albany, and no one wants to entertain a crossband system.
Fascinating. I'm wondering if perhaps the antenna on the roof just needs to be higher to escape the cloud. I can think of a similar issue I had with a friends class C RV. While in motion, the entire RV would have a giant RF cloud while in motion that took out anywhere between 50 to 300 Mhz. We could never figure it out and we nearly replaced all cabin and cab electrical systems trying to fix it. What I ended up discovering was that if we got the antenna about a foot higher in the air on the roof, the problem went away. Since we were coming close to the 13.8 foot USDOT height limit, we decided to build a little antenna bracket extending out foward at the front on the little over cab bed section about a foot with a NMO mount clamp we made up and we were in business.

I dunno if you can get a higher antenna of some sort on the DMU, but that might be an idea. I have a sudden picture of a DMU with a NMO mag mount with a Larson NMO150 on the top :P
Mountain Wave Search & Rescue http://www.mwave.org
Support Search & Rescue: Get Lost!
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

Interesting you should mention an elevated feed antenna because that is what I'm considering after todays testing. I ran a 35ft RG58 cable outdoors with a mag mnt and got 4db of desense. I could get as close as 2 feet away from a closed section of the body before the radio squelched. Waving the antenna in front of an open door or a window (even many feet away) caused the squelch to close. We found a place above the door near the coolant storage tank that got us back almost 6db with the ant stuck to the hull roof. We're going to let it run for a few days. While I was on the roof, if I did a Statue of Liberty, the desense was beautiful. It was back down to 6db total compared to the 20db where we started this morning. So, I'll fab something up that can take some abuse without destroying whatever it will be attached to if a hungry tree limb reaches for it.

I want to make an aperture antenna welded to the body offset by quarter wave stubs, but we're only allowed a four inch clearance from the sides. Rats. they poo-pooed the NXU through the cellphone intertubes fer sure. Cingular / AT&T has had too many coverage / service continuity issues and they are considering another provider.
KE7JFF
Posts: 270
Joined: Sun Nov 02, 2008 7:27 pm
What radios do you own?: MX300 lunchbox

Re: Vehicle noise at 160mhz

Post by KE7JFF »

Bill_G wrote:Interesting you should mention an elevated feed antenna because that is what I'm considering after todays testing. I ran a 35ft RG58 cable outdoors with a mag mnt and got 4db of desense. I could get as close as 2 feet away from a closed section of the body before the radio squelched. Waving the antenna in front of an open door or a window (even many feet away) caused the squelch to close. We found a place above the door near the coolant storage tank that got us back almost 6db with the ant stuck to the hull roof. We're going to let it run for a few days. While I was on the roof, if I did a Statue of Liberty, the desense was beautiful. It was back down to 6db total compared to the 20db where we started this morning. So, I'll fab something up that can take some abuse without destroying whatever it will be attached to if a hungry tree limb reaches for it.

I want to make an aperture antenna welded to the body offset by quarter wave stubs, but we're only allowed a four inch clearance from the sides. Rats. they poo-pooed the NXU through the cellphone intertubes fer sure. Cingular / AT&T has had too many coverage / service continuity issues and they are considering another provider.
I'm surprised Clear hasn't given you guys something for the DMUs. That would a slick advertisement for their service!

The next few days with a magmount on the roof while in service? Heh, I have a sudden urge to hop on a train to take a photo of that :)
Mountain Wave Search & Rescue http://www.mwave.org
Support Search & Rescue: Get Lost!
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

Continuing to chase the noise. Ran into some problems with comparator incorrect site voting. Created a pretty prop map to show expected rcvr coverage.

Image
AEC
No Longer Registered
Posts: 1889
Joined: Wed Dec 22, 2004 7:56 pm

Re: Vehicle noise at 160mhz

Post by AEC »

In all of this, I didn't notice any questions about antennas, and I think the sharkfins are of the 1/4 wave design, which is noisier than a 1/2 wave.

Being what they are, the 1/2 wave requires no GP and this may lower the noise floor by several dB.

Plus by design, one could mount such a beast on top without having to worry about a solid connection to the body of the car.

I have extrememly limited experience with rail systems, and none with passenger movement rail, my experience deals with freight hauling mining ore to smelters/crushers, Etc...

The engines used on both lines here are GP series and a few newer ACE(I think) engines by GE.

Nothing but diesel fuel converted to AC for the traction motors, and all contained in a single area, and certainly none of the electronics you are having to work with and around.

You do indeed, have your work cut out for you here.

My sincerest appologies :-(
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

The coach manufacturer installed the ASP sharkfins, and they are a "lower tier" product fer sure. Rattle buckets of bent aluminum riveted together with a plastic cover sure to give a lifetime of noise. And! they are mounted on large metallic surfaces that also serve as access panels to the cooling system and HVAC which may or may not be fully tightened down. And! They are mounted next to aluminum louvered sidepanel facades to hide all the aforementioned roof mounted equipment so as not to disturb the eye of the public beholder with such mechanical visual blight, and to maintain the sleekness of the railcar. Those louvers are securely attached and do not rattle. Of course. But wait - There's more! We have a height limit. There is a low bridge, and these cars clear it by 4 feet, and we are not allowed to encroach that space by more than a foot leaving three feet of no fly zone. So even a quarter wave on top of the mechanical equipment would technically be too high. A half wave would probably be out of the question.
AEC
No Longer Registered
Posts: 1889
Joined: Wed Dec 22, 2004 7:56 pm

Re: Vehicle noise at 160mhz

Post by AEC »

Might be time to investigate one of those Antennex phantom antennas...Or as i like to call the VHF models: Garbage cans.

Never had the uses you have, and surely no idea as to the suitability of such as you have with height restrictions....Sounds like bean counters in control
of everything NOT understood by them.

Brain? Brain? What is Brain?

*Insert bean counter insult here* You green blooded, inhuman......
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

The one I have from Larsen is too freq specific. It's about the size of a squat can of beans. Screws on to an NMO mount. If they stayed on one channel, it might work. But, they have two other channels that are outside the adjustable bandwidth, and the mfg note with the antenna has BIG LETTERS warning about possible burnup, loss of warranty, etc, etc. So, I've been chicken to try it. Looks cool though, and would definitely clear the bridge whose private owners set the policy. I don't know if the draggers would spot an overheight antenna or not. If they did, the cab signals would kill the drive, put on the brakes, and send the crew scurrying for whatever set off the automated safety equipment. I am sure they would be very pleased with me. Nothing but love notes in my inbox fer sure. God bless the machine.
AEC
No Longer Registered
Posts: 1889
Joined: Wed Dec 22, 2004 7:56 pm

Re: Vehicle noise at 160mhz

Post by AEC »

You certainly have far too much B.S to wade through.

Too bad the red tape fiasco kills creativity, and if you HAD a more open availability for minor adjustments to their set-in-stone plans, I would think you could
come up with an entirely effective workaround that pleases the eyes and pockets.

They want though outside the box within the confines of two square millimeters of free space.

Hold a pity party for those morons once they realize the answer isn't a simple yes or no to the problem/s.
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

It's part of the challenge, and I thrive in that environment. Think of it as the toughest sudoku you've ever tried to solve.

Made some progress with my outbound from the trains breaking up problem - the voter inappropriately choosing rcvrs. It's the weirdest thing. In certain areas well served by the repeater, the voter chooses the choppy signal from one of the other two rcvrs. I'll be looking at it tomorrow when there are only a couple freight trains scheduled through.
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

How do voters work? By choosing least noise.

What's the difference between the three sites? The main rcvr is direct to the comparator, and the other two arrive via dsl/nxu link. Doh!

The nxu's are rolling off the noise, and being voted even though they are actually the worst because of picket fencing causing sq gate chop.

Line equalization time though in reality my task will be to equalize the local rcvr to match the nxu's, not try to decrease the rolloff of the nxu's. I could run the local rx through a pair of back to back nxu's, but that will be my last resort. Too clunky. A simple rc network should do the trick.
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

That worked. I beat it into submission. It's a real live actual voting system! Shazaam.

But, I'll wait for the roses and cigars until after da boyz use it this coming week.
User avatar
apco25
Posts: 2685
Joined: Tue Oct 30, 2001 4:00 pm
What radios do you own?: APX / Astro 25 / Harris

Re: Vehicle noise at 160mhz

Post by apco25 »

Just a couple quick suggestions, but you may want to investigate REAL railroad antennas such as those made by sinclair - they are not some cheap piece of plastic with aluminium inside.

http://www.dpdproductions.com/photos_rr ... io/149.jpg UHF version but physicall same as their VHF product.

Have you made any investigation of the AAR frequency base infrastructure they are using?
"Some men just don't know their limitations"
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

As a matter of fact I've looked at DPD's site before. Most of their equipment is standard quality. Good prices and good enough for personal use. On the infrastructure - yes, I've spent a bit of time on it. I made some significant progress on the repeater inbound over the weekend, but I'll wait to pour the champagne for a few days. There was a subtle difference in the C msg filter through the roip than the local rcvr. I accounted for the difference and equalized it weighting the system in favor of the main receiver. Time will tell if Ii did it right. If so, then I can again focus on the train inbound desense from all the equipment. I'm still not certain how to address that and stay within the height limitations set by the bridge.
KE7JFF
Posts: 270
Joined: Sun Nov 02, 2008 7:27 pm
What radios do you own?: MX300 lunchbox

Re: Vehicle noise at 160mhz

Post by KE7JFF »

Bill_G wrote:As a matter of fact I've looked at DPD's site before. Most of their equipment is standard quality. Good prices and good enough for personal use. On the infrastructure - yes, I've spent a bit of time on it. I made some significant progress on the repeater inbound over the weekend, but I'll wait to pour the champagne for a few days. There was a subtle difference in the C msg filter through the roip than the local rcvr. I accounted for the difference and equalized it weighting the system in favor of the main receiver. Time will tell if Ii did it right. If so, then I can again focus on the train inbound desense from all the equipment. I'm still not certain how to address that and stay within the height limitations set by the bridge.
Have you talked to PWNR about what is THEIR height limit?
Mountain Wave Search & Rescue http://www.mwave.org
Support Search & Rescue: Get Lost!
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

They are the bridge owners and set the limits.
RADIOMAN2002
Posts: 1102
Joined: Thu Apr 04, 2002 4:00 pm
What radios do you own?: More than I can count

Re: Vehicle noise at 160mhz

Post by RADIOMAN2002 »

While I havn't read the whole response from everyone on this problem at our RR we have found an abundance of noise being generated by any computer switching power supply, even the ones that drive the sign boards at the stations. So if your equipment has anything in the way of any type of computer style switching supply, which is quite likely, you may have to relocate you antenna if possible, try a shorted stub antenna(not very likely to correct problem but worth a try)or go back to manufacturer and demand a solution from them for the noise. We had to do this recently when a switching power supply(rail to 72v) put a 3 rd harmonic right on our RTC channel.
Thinking more about this, relocating the radio away from the electrical cabinet with all the noise is probably going to be your best solution, with a remote control head using a good control cable. Don't use the flat ribbon cable that comes with the kit, but Cat-6 network cable, it has twists that should cut down on cross interference, or shielded would be even better. For an antenna try using the old style, if they are still available German Handgrenade style antenna, ( will have to get the number, don't have it handy) built well and basically bulletproof. But in addition to I would definitely let my design engineers know about this problem, and put in any succeeding bids that the vendor correct these problems.
Now as far as voters are concerned, if your receivers are not of all the same type and brand you can get ISSUES. I had a voter system for one of my repeaters, using RF links back to the main site. The issue turned out to be we had many different brands and types of link TX'rs. This caused problems with the frequency roll off of the received audio signal going back to the main site. We had to equalize each received signal through each link to the output of the link receiver at the site to get it to stop voting on the worst signal.
Motorola has equalizers on their equipment, but first you need to sweep your line or link to get a baseline of where the transference of signal is not linear. I'm guessing you have phone lines, if so you have to sweep them (300 to 3000hz)and if out of spec tell telco to give you a properly equalized circuit.
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

Hi radioman. Great ideas. I appreciate your thinking about this problem because this project brought some big brahmas to the learning curve rodeo.

Made some progress on the overall issues -

Re-equalizing the rcvrs into the comparator solved a lot of problems. Love notes from the dispatchers and supervisors have dropped to zero. Folks are talking on it all day and they aren't having to repeat themselves a hundred times. Time to put the Maytag label on it, and let this one slip quietly into history.

Installed an isolated ground half wave on one of the DMU's. Through experimentation I found a quieter location on the roof that also has mounting options that won't be a maintenance headache. I used a small aluminum plate, and an isolator with a wall cleat from a Harger bar to give me a physically strong but electrically isolated mounting surface for the half wave. They are all commonly available parts, and the assembly is just short enough to clear their height limitations. I measured greater than 20db desense before I started, and had less than 18db of desense when I finished. We'll call it 3db. Not much improvement, but decoupling the ground at the mount did make some difference. In a service area where the worst case signal strength is in the -90 range, 3db will give the rcvr a little margin where it is needed. Airchecks were good in the known bad spots. Fingers are crossed, and we're marching forward.
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

A little over a month has passed since I put the end fed half wave antenna on isolated ground into service, and it sounds great. Consistently, it comes through with greater quieting than the ASP low profile transit antennas. I have gotten no feedback about the receive quality. However, I hear the crews using the transit antennas asking for repeated instructions often enough to suspect the decreased noise from the isolated ground is real and effective. Now it's just a matter of getting authorization to proceed on the other trains which may be slow in coming. Decreased revenues and budget cuts have forced prioritization of maintenance, and if it ain't broke, it ain't getting fixed.
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

Quick update on this problem - everything is working so well, none of the supervisors responded to email requests to authorize upgrading all the trains to isolated half waves. I'd love to close this project. I quit emailing, and started personally visiting each man up the command to get his input. I suspect it will move into the next FY.
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

Mission Accomplished!

I got the go ahead to neatenfy the prototype and standardize the antennas on the remaining DMU's. Our guys knocked it out in a couple days, and what a difference it made. The crews are reporting they can hear the draggers now as well as each other in areas they thought were dead before which was the main intent of the isolated mount. They are also reporting greater range on their simplex yard channel. We put in brand new standard RG58 to get the stranded center conductor since the solid center conductor of the existing LMR200 was breaking at the pin from vibration becoming a general maintenance issue.

Project closed.
User avatar
MSS-Dave
Posts: 770
Joined: Mon Jun 30, 2003 6:02 pm
What radios do you own?: XTL5K, NX300, PD782, Spark Gap

Re: Vehicle noise at 160mhz

Post by MSS-Dave »

Bill...

Just want to say thanks to you and the others for posting such detailed info on the problem and corrections to this issue. I know nothing about trains or communications going on with them but I put your case in my "reference" file in case I have something simular come up in my side of things (Power Utility trucks..)

Thanks!

Dave
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

You're welcome Dave. Trying to find and suppress all the vehicle noise sources for high band radios can be a challenge. I've played stump the chump many times - sometimes I win, sometimes I lose. Hopefully you can get it down to acceptable levels so the radio functions.
KE7JFF
Posts: 270
Joined: Sun Nov 02, 2008 7:27 pm
What radios do you own?: MX300 lunchbox

Re: Vehicle noise at 160mhz

Post by KE7JFF »

I think I might take a trip on said rail line today to hear your work :P
Mountain Wave Search & Rescue http://www.mwave.org
Support Search & Rescue: Get Lost!
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

We'll just to make sure there are trespassers, or something almost as exciting, so they'll use the radios. :lol:
joescanner
Posts: 31
Joined: Fri Nov 30, 2001 4:00 pm

Re: Vehicle noise at 160mhz

Post by joescanner »

Heh.. the weather is heating up. That should be enough (said the man 80 miles north of Albany...)
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

Joe - Do you guys still listen to them, or has the blush gone from the rose yet?
joescanner
Posts: 31
Joined: Fri Nov 30, 2001 4:00 pm

Re: Vehicle noise at 160mhz

Post by joescanner »

We turn the radio on when we hear of issues, primarily, and of course every once in a while when things are a little "boring" (to try and use a word that Murphy might not hear...)
KE7JFF
Posts: 270
Joined: Sun Nov 02, 2008 7:27 pm
What radios do you own?: MX300 lunchbox

Re: Vehicle noise at 160mhz

Post by KE7JFF »

joescanner wrote:We turn the radio on when we hear of issues, primarily, and of course every once in a while when things are a little "boring" (to try and use a word that Murphy might not hear...)
I would think in your line of work, you would describe it as "routine"
Mountain Wave Search & Rescue http://www.mwave.org
Support Search & Rescue: Get Lost!
User avatar
Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Vehicle noise at 160mhz

Post by Bill_G »

We like the routine, or more correctly, we like staying ahead of the outages so Joe's day stays routine. I don't do much on his side of the house. They've got some good maintainers. On the other side of the house I can see the whole system from other locations, and reading the tea leaves know where to focus my maintenance so that everything stays routine usually fixing it without them knowing something happened. I love it when I get challenged by a new dispatcher when I come in occasionally to clear the log files in the alarm system. Who's this guy??? as I log into a work station at an open position. Every once in a blue moon a headset jack or a foot pedal dies. That's about as exciting as I let it get. OTOH, the MOW guys have all the fun. Never a dull moment. We like the routine. Now, if a few members of the public would just cooperate ...
Post Reply

Return to “Vehicle Radio Installs”