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2 Radios.....1 antenna?

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nrembis

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Hi folks, I dont have the funding for dualhead radios,so what would be the best route for me to wire 2 vhf radios on 1 antenna, I need to be able to use the 2 radios whether im sitting in the cab of the truck or using the 2nd radio in the bed of truck. Both radios will be on at all times.

Thanks!
 

nrembis

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Ive seen those but all of them listed had a 30w limit, im pushing 50-100w in the 151mhz-159mhz range. Im not sure if I could use an antenna on each radio without feedback issues. Im not sure how apart each antenna would have to be to keep from having each radio interfering with each other.
 

majoco

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How do you propose matching the antenna to the radios and how do you stop the transmitted power from going into the other radio? Not a practical soulution IMHO. Why not just have two antennas?
 

nrembis

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Why not just have two antennas?
I'm not sure how close I could have 2 antennas operating on the same frequencies without problems. I know if Im anywhere near my mobile with my portable and keyup I have massive feedback issues. I dont want that problem on the truck having 2 mobiles close together.
 

W2NJS

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Comet is a company that makes the same type unit, their CF-4160, which costs somewhere around $50. I'm in the process of installing one on my new APX7500 dualband mobile in my Outback so I'll be able to use just one antenna. The radio has separate VHF and UHF outputs.
 

prcguy

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I think some people are mistaking the recommended Shakespeare RF controlled switch with a diplexer or some other device.

The Shakespeare switch allows two VHF radios to connect to one antenna and when you key either radio it senses the RF and switches the antenna to that radio and disconnects the other radio from the antenna. There would never be a time when one radio could transmit directly into the other radio with this switch.

I suspect it will handle 100w without any problems.
prcguy
 

n5ims

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I'm not sure how close I could have 2 antennas operating on the same frequencies without problems. I know if Im anywhere near my mobile with my portable and keyup I have massive feedback issues. I dont want that problem on the truck having 2 mobiles close together.
Please be aware that the feedback you hear (that screaming wail or whistle) has nothing to do with the antennas, but the sound from one radio's speaker being picked up by the mic of the radio transmitting on the same channel. This can be solved simply by turning down the audio on the radio not being used to transmit on at that moment. You may also need noise canceling mics and proper speaker placement to direct the sound from one radio away from the other's mic location when transmitting (like the speaker in the cab facing forward and that in the bed facing rearward).

One issue you'll need to address is having the antennas seperated by some distance (at least a yard or more apart on 150 MHz) to help reduce the transmission from one radio overloading the other radio that's receiving (vertical seperation is even more helpful if possible like one antenna on the hood and the other on the roof). This is less critical using "real" radios since they're designed to handle strong signals, but may still be an issue with higher power radios (as you indicate you use 100 watts).
 

W2NJS

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Going back and re-reading the Shakespeare sheet I note that it requires 12VDC whereas the Comet unit does not, but the Comet is definitely a VHF/UHF unit, not a VHF/VHF as the OP is seeking.
 

davidgcet

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do you need to be able to change channels from the bed? if not then just run a mic and a speaker off the accy plug. you can use a powered speaker with volume control if you need it.
 

nrembis

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do you need to be able to change channels from the bed? if not then just run a mic and a speaker off the accy plug. you can use a powered speaker with volume control if you need it.
Yes, I need full radio controls from the rear of the truck, so extra mic and speaker wont cut it. If I can use 2 antennas without problems I dont have an issue with doing that. I just figured I couldnt put 2 together that closely and would have to use an automatic switch of sorts and 1 antenna for both radios
 

prcguy

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They are two completely different things. The Comet is a diplexer, or a high pass and low pass filter with a common connection and the Shakespeare is a remote antenna switch with RF sensing to automatically connect the antenna to the last radio that transmitted.

You can have a VHF/VHF diplexer but it would have to split the band in two and one radio would be dedicated to high VHF freqs and the other radio to lower VHF freqs.

The Shakespeare will probably work across a wide range of frequencies but since its marketed for the marine industry they only mention VHF.
prcguy


Going back and re-reading the Shakespeare sheet I note that it requires 12VDC whereas the Comet unit does not, but the Comet is definitely a VHF/UHF unit, not a VHF/VHF as the OP is seeking.
 

zz0468

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I'm not sure how close I could have 2 antennas operating on the same frequencies without problems. I know if Im anywhere near my mobile with my portable and keyup I have massive feedback issues. I dont want that problem on the truck having 2 mobiles close together.
You're going to have acoustic feedback problems regardless of how you chose to handle the antennas. A receiver disconnected from an antenna, but co-located with a transmitter on the same frequency WILL hear it just fine.
 

N0BDW

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Hi folks,

I don't mean to hijack this thread but I think I have the same / similar question and as of yet have not seen an answer.

Our ambulance and fire department share a building. We also share a simplex low band frequency (46.xx). We have two base radios, and one tower. Currently the ambulance base runs off a mobile antenna with inadequate ground plane (attached to the side of the building). It works okay for transmitting (dispatch can hear us, which is the important part), but sucks for receiving. I would much prefer to get this radio using the same antenna as the fire base, which is up on the top of the tower (much better RX).

Is it possible to use two transmitters that use the same frequencies on a single antenna for less money than putting a 2nd antenna and coax up on the tower? Also: if we were to do such a thing, isn't the vertical separation required going to kill us? The tower is ~50 ft if I had to guess.

The other thought I had is to hook up the base antenna to the scanner which is hooked to the PA system, then turn the volume all the way down on the base. Both base radios could be connected to mobile antennas on the sides of the building for transmitting, and then we'd be able to listen to all radio traffic over the PA (with the better RX of the base antenna).

Thanks!
 

zz0468

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Is it possible to use two transmitters that use the same frequencies on a single antenna for less money than putting a 2nd antenna and coax up on the tower?
No. There are things that CAN be done, but it's messy, and probably not cheap.

The other thought I had is to hook up the base antenna to the scanner which is hooked to the PA system, then turn the volume all the way down on the base.
You don't want to do that. Scanners are actually horrible receivers, and if you have a REAL low band base radio, that's what you want to listen to.

The proper way to handle your situation is to configure the base station for wireline operation, and then use two wireline remotes, one for each half of the operation. That way, both dispatchers hear each other, and both transmit and receive off of one base station. There's one antenna on the tower, and if you need a PA feed from the radio, you can tap off the wireline and feed both transmit and receive audio to the PA.

Wireline remotes are relatively inexpensive, too.
 
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N0BDW

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No. There are things that CAN be done, but it's messy, and probably not cheap.



You don't want to do that. Scanners are actually horrible receivers, and if you have a REAL low band base radio, that's what you want to listen to.

The proper way to handle your situation is to configure the base station for wireline operation, and then use two wireline remotes, one for each half of the operation. That way, both dispatchers hear each other, and bot transmit and receive off of one base station. There's one antenna on the tower, and of you need a PA feed from the radio, you can tap off the wireline and feed both transmit and receive audio to the PA.

Wireline remotes are relatively inexpensive, too.
I guess that depends on your definition of "real." We have a CDM1250 on the fire side, and an older radio (Syntor?) on the EMS side. We don't do any dispatching on our end of things, the county dispatches for us.

So, not anything I personally would actually call a "base" but it is used as a "base" and is labeled a "base" in the system ("Livonia Base").

I'm not familiar with the type of setup you are describing. Would that be possible with our setup? Please let me know if you need any more details.
 

zz0468

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Ok, that's doable. There is a device called a "tone remote adapter" that gets added to the CDM1250. This allows it to be controlled by the tone remotes. Talk to your friendly two-way radio technician. None of this is anything that is easily done by an end user, but it's a no-brainer for a reasonably competent technician.

Any two-way shop will know what a tone remote is.
 
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