Cheap way to connect two mobiles to one antenna?

Post by Pj » Mon Sep 27, 2004 4:50 pm

Ok, word here is cheap.

Since MA/COM doesn't want to give up the details for expanded recieve, or tx/rx on a 35-50 mobile, I am thinking of adding in the lowsplit orion in a dual radio setup. The catch is, I DO NOT WANT another lowband antenna on the the truck, so I would like to hook up both radios to my current one.

What's out there that isn't exotic?

Cowthief · Post by **Cowthief** » Mon Sep 27, 2004 5:05 pm

Hello.

You want to connect 2 radios, in the same bandspread, to one antenna?!
You would be lucky if you did nut burn out both radios with 2 antennas.
The military makes this work by having an RF switch, only one transmitter is connected to the antenna, the other radio sees ground.
Only a small number of radios can do the entire lo-band.
AFAIK the only radios that can do really large bandspread with one antenna are the military radios.
Remember, you will need to somehow match both radios to this one antenna that is tuned to whatever center frequency, no real easy task.
If all you want is analog AM or FM, and you are not real picky with legal issues, then a military radio is the way to go.
If you are picky, then the syntor X is the way to go, but remember, just because the radio can do the entire band does not mean the antenna can.

nmfire10 · Post by **nmfire10** » Mon Sep 27, 2004 6:52 pm

Umm, yea.

Get an antenna relay that will disconnect one radio when you PTT on the other. I know they exist but I couldn't help you with where to look.

Cowthief · Post by **Cowthief** » Mon Sep 27, 2004 7:33 pm

Hello.

You COULD simply use PN juction diodes, just like that in most modern radios.
The trouble is two fold.
One, you are directly coupling the two radios RF front ends.
Just like connecting scanners, you want some form of isolation.
The other, even more important issue, what about the bandspread of the antenna.
On lo-band, the bandspread of MOST antennas is usually just a MHz, perhaps a little more.
To do 30MHz to 50MHz, for example, military radios use a tuning device at the base of the monopole antenna, the early models actually used a motor and switch, you could manually select what part of the band you wanted if the autoselect failed.
Most miltary radios, like the AN/PRC25/77 or AN/VRC12 go from 30MHz to 76MHz
The URC 1xx series is a dual band radio.
There is a model that will do 30MHz to 88MHz and 118MHz to 172MHz.
The trouble in making a radio that wideband, and making it work correctly, is quite an undertaking.
The current radios now go from 30MHz to 512MHz with no gaps, but you are not going to find one on the surplus market anytime soon.

raymond345 · Post by **raymond345** » Tue Sep 28, 2004 1:25 am

you have two each 50 ohm loads here.
when you wire them together you get
25 ohm output.
Well the word is CHEAP.
use an antenna switcher.It is the cheapest
way to go.

The normal was is a duplexer.
What is the frequency difference between the two radios?

Post by Pj » Tue Sep 28, 2004 3:46 am

Its two 100 watt lowband orions.... 30-42ish and 35-50ish. Antenna switcher is out as I need to monitor both ranges, then transmit on whichever radio is needed.

Yes I know there is an antenna difference, but its cut and works in the ranges needed...so I am all set there.

Makes/models/prices?

wa2zdy · Post by **wa2zdy** » Tue Sep 28, 2004 11:57 am

I see some fried front ends here. 100w radios . . . yeah. If they were 25, and one input was grounded while the other transmitted, maybe.

Duplexer would work if the separation is enough, but have you ever seen a low band duplexer? They aren't trunk mounted affairs to be sure.

I don't know what to suggest. This is a tough one.

Will · Post by **Will** » Tue Sep 28, 2004 12:10 pm

There was a dual receiver that CHP used, MICOR/ MOTRAC. Also used in the current GE/Erickson CHP low band radios. (California Highway Patrol)

They use a coaxial splitter AFTER the antenna relay to feed the second receiver.

The antenna relays used in the Mocom70 and some base stations could be used to switch out the other radio completely using the relay driver allready in the Syntor. Not sure if the antenna switching circuit in the Orion is simmular.

KitN1MCC · Post by **KitN1MCC** » Tue Sep 28, 2004 1:55 pm

austin antenna will build u an antenna that will work for you they run about 99 to 150 dollars but they can buildthem to your spec and frequency range

i know thye just built one for the town of glastonbury that will work on both 35mhz and on 800mhz it does have a box to hook the radio together

mike scranton has the info for them or check out

http://www.austinantenna.com/

thebigphish · Post by **thebigphish** » Tue Sep 28, 2004 8:57 pm

KitN1MCC wrote: i know thye just built one for the town of glastonbury that will work on both 35mhz and on 800mhz it does have a box to hook the radio together

...{growl} those GD towns with all their GD money....you guys see those new ambulances they bought to keep their bank accts in "volunteer" range?
{/growl}

007 · Post by **007** » Tue Sep 28, 2004 10:01 pm

Will wrote:There was a dual receiver that CHP used, MICOR/ MOTRAC. Also used in the current GE/Erickson CHP low band radios. (California Highway Patrol)

They use a coaxial splitter AFTER the antenna relay to feed the second receiver.

The antenna relays used in the Mocom70 and some base stations could be used to switch out the other radio completely using the relay driver allready in the Syntor. Not sure if the antenna switching circuit in the Orion is simmular.

The antenna relay box in the CHP cars is not being used to split multiple transceivers.

The current CHP lowband radio is the GE Rangr, and it covers all the freqs in the state. No second receiver required. The unit mounted next to the Rangr is a highband Mastr-Exec II (or a Pyramid in new installs) used as the vehicular repeater.

The relay box is used to combine the vehicular repeater and the Uniden scanner onto one glass mount VHF antenna. The lowband GE Rangr gets it's own Antenex base loaded 1/4 wave on the roof.

As for Pj's problem, the only real "easy" way is to get a relay box and run both Orions into it, with a common lowband antenna. When you xmit with radio "A", then radio "B" is electrically isolated until you unkey.

Tue Sep 28, 2004 11:03 pm

Pj wrote:Ok, word here is cheap.

You cheap bastard!

Why not just get a Syntor 9000 and make all of your troubles disappear? 6 meters, 11 meters and everything in between!

apco25 · Post by **apco25** » Tue Sep 28, 2004 11:55 pm

heh cuz the Orion isnt the size of 68 caddy's trunk (Jimmy Hoffa not included)

I did the same thing with my Orions - dual lowband tray configs using a relay.

Works fine.

grinthock · Post by **grinthock** » Wed Sep 29, 2004 5:03 am

I've seen (but don't ask me where)

nd auto antenna switch, has isolators in it, and cuts off the 2nd radio's feed line when you transmit on the 1st.

All in all, to be honest, I think this is a stupid idea. 100W is going to screw up just about anything. I don't know that any isolator/splitter is going to stop 100W. Nor do I think the one I saw was good for 100W.

Do yourself a favor, get 2 antennas (but even then, i'm not sure that even if the antenna's were spaced out you wouldn't blow stuff)

mastr · Post by **mastr** » Wed Sep 29, 2004 10:35 am

Fair Radio has the CU2194/urc diplexer listed. It is tunable over 30-76 Mhz. It isn't an ideal solution, but a good start toward one.

kd9000 · Post by **kd9000** » Wed Sep 29, 2004 9:06 pm

Syntor X 9000 is the way to go. If your xmit freqs aren't too far apart, Antennex makes a wide band low band antenna. I measured 1.7:1 and lower between 47-54 MHz. Of course, the lower you go in freq, the less spread you can get.

Ken

Will · Post by **Will** » Thu Sep 30, 2004 12:48 am

The CHP uses a antenna relay box which disconnects the other radio, usally a scanner, when the Ranger transmits. The newer CHP radios are the Orion and Jaguar, and use a simmular antenna switch relay box. The GE Ranger, Orion and Jaguar radios do not have the second receiver.

The mobile radios made by Motorola, were the Motrac, Motran, and later the "Micor" model a special production unit, type X71RTA-4413AA, Micor radio.
These were 100 Watt transmitter types which had dual receivers, such that the patrol cars could hear the transmissions of nearby cars as well as the station, when the other cars were in the normal "car to station" mode.

Cheap way to connect two mobiles to one antenna?

Cheap way to connect two mobiles to one antenna?

I would not.

Antenna relay.

50 ohm loads

Re: Cheap way to connect two mobiles to one antenna?