Batboard

Hey guys,
With the high frequency of the 800mhz radios, do you find a significant performance drop when using a stubby antenna on the radio? Also from experience has anyone found a significant performance increase when using the "public safety" speaker microphone.
Thanks,
David

Yes and no. That's why we put so much effort into site receiver performance. All system metrics are based on portable performance. The public safety mic with the integrated antenna is high maintenance item. We don't use them.

If you are using a single site system or operate on fringe areas of coverage and you put the stubby on the radio and carry on your belt, it's a huge difference. Been there, done that on 900. Users found the short antennas, THEN found speaker microphone (not PSM type). It was amazing to hear them :o and whine that the SYSTEM was bad. If you are using a system engineered for portable coverage which is usually using PSMs in a public safety application, it's shouldn't be too bad. I have been testing a lot with short antennas on the radio in a 10 site simulcast Astro system and they work better than I expected. Some of the users live outside of the intended coverage area and there is a definite difference referenced to the stock whip.

Like Bill_G said, it's going to depend almost exclusively on how the system is designed and performance of the RX system. I think stubbies are rated at -6 to -8 dB gain so your uplink ERP is already reduced to less than a watt. Put that behind a body and add another 15-20 dB of attenuation. You probably see where I'm going....

Dave

My experience has been that when using a "city wide" system, you are better off using a standard antenna, even if it is multi site. There are tree lines and other obstructions that render a stubby almost useless...unless you want to keep repeating your last transmission...The only systems I have observed that can use a stubby all the time, and get away with it are the "industrial" systems... for example UPS , GE and Ford Motor Co all have systems for use at their facility and no matter where they are in the facility, they are probably a stone throw from the system's antenna....

Does the coax in the PSM add any additional performance? Thanks for everyone's input!

Motorola engineers conducted extensive tests of various portable antenna types for each of the frequency bands. They documented their results in a paper which was published in the IEEE Transactions on Vehicular Technology. Similar results are also contained in Table D-5 in TSB-88.1-C.

Using a quarter-wave antenna [stubby] results in a considerable performance loss compared to either a coaxial dipole or an end-fed half wave. On 800 MHz systems, when the radio is worn at hip level, the quarter wave loss compared to a coaxial dipole is 6.9 dB.

With a quarter wave antenna held at head level, the results are very close to a dipole worn at hip level.

Because the end-fed half wave antenna's performance is much closer that of the coaxial dipole, that antenna is pretty much the 'normal' antenna for 800 portable use these days.

WOW thats some great information guys! What is your comment on the VHF stubby antennas that are being sold on ebay? I know that when big M themselves will not sell a VHF stubby and the only place you can get one is ebay, that has to say something in itself. What do you think of a Chinese ebay VHF stubby's, could that do damage to the radio?
David

Motorola sells at least 2 VHF stubby antenna's HAD9742 MX thread and RAD4194 SMA thread I have both.

dsheli wrote:I know that when big M themselves will not sell a VHF stubby and the only place you can get one is ebay, that has to say something in itself.

Moto sells VHF stubby antennas.. They've offered them for years now. RAD4194A is a 150-162 MHz, 3.55" with an SMA connector just to name one..


-Marc

Wow I stand corrected, I just assumed they did not sell them because I could never find one.
David

When we were doing the coverage maps for our 800 system back in 2000 we utilized .5 watt ERP for the 800 radio with PS speaker mic and 1/4 wave antenna placed on top. When we ran the maps we had very clean maps with very little open areas down to 15db loss buildings. When we ran the same maps with the 1/2 wave antenna on the waist factoring in body shielding it actually looked worse on talk-back, which in our case was the limiting factor. I'm sure this would get worse with those that have serious dunlap disease.

If this is an operational decision for a PS system it would be best for the vendor to supply coverage maps for multiple configurations as YMMV based on the design of the system (voted, simulcast, sibgle site, etc.).

One thing for sure, this model antenna does not work very well in our tests even though I have seen officers from other agencies using it on their radio.

Updated link....

http://www.tessco.com/products/displayP ... ventPage=1

you can't hotlink images from tessco and being the douchebags they are, they have also set (or tried to set) a cookie on everyone's machine who has viewed this thread.

My bad...was not aware of that. I updated the link.

that antenna is a piece of junk.
and the local MSS will not honor their service agreement if someone shows up with one on their radio, citing it not a suitable replacement part.
if you've ever swept one you'd see why.

I've seen that used, at least for RX (but was on an authorized radio) and worked (RX is all I saw) pretty well for the location and building we were in.

Not that I would use that, but for a throw radio for some people for quick and dirty things..

As to the other stuff above, I started a similar thread. For my uses, I started with the dipole antenna, and now use the 1/4 wave. Generally speaking, both are performing the same in my capacity. I have the 1/4 wave on right now, and in a general fringe range and getting an RSSI of 78. With the dipole, it goes to about 82.

When I am really on a fringe range, the dipole RX's better, but Tx works the same...no go.

xmo wrote:Motorola engineers conducted extensive tests of various portable antenna types for each of the frequency bands. They documented their results in a paper which was published in the IEEE Transactions on Vehicular Technology.

If anyone is interested in reading this, it is in Volume 40, number 4 (November 1991). I thought it was interesting.

Back to basics, no testing or field experience taken into account:

1. The TESSCO 800 mHz antenna on that link is only two inches long, and even though it's probably helically wound the fact is that a quarter-wave at 860 mHz is only 3.25 inches long,
so if you can find a straight antenna that's 3.25 inches long you're probably ahead of the game right from the start.

2. So a half-wave, end-fed 860 mhz antenna would be about 6.5 inches long. Even better.

(Neither of the antennas mentioned above would be helically wound, and are essentially end-fed, straight wires.)

3. And the much longer, center-fed, 800 mHz antenna is certainly the best bet for all around use. Of course you've got an antenna that's about 8 inches long, which will poke you in the eye maybe at times, but the transmitted and received signal should be far superior to the other two antennas mentioned above.

To answer one poster's question about PS speaker/mics, the answer is no, the coax from the radio to the microphone's antenna mount should not radiate.