VHF Duplexer using repeater as a base

[lancerice]

I have a VHF repeater and a base using 2 gm300 radios working with dual antennas but I can't get the speration, I am running with a 4.8mhz split with 20ft horizontal and 10ft vertical speration, I have now tried to use a duplexer I have had it tuned to my frequencies but when it is installed as a repeater it seems to work but when I want to use it as a base the radio that rx is the radio that I need to use to tx as a base, I think this is due to the duplexer being tuned to the rx frequency not the tx frequency, when these duplexers are tuned can the radio's only be used on that frequency only. If any one can help me with this please I would be most grateful, Thanks Lance

[Jim202]

I have a VHF repeater and a base using 2 gm300 radios working with dual antennas but I can't get the speration, I am running with a 4.8mhz split with 20ft horizontal and 10ft vertical speration, I have now tried to use a duplexer I have had it tuned to my frequencies but when it is installed as a repeater it seems to work but when I want to use it as a base the radio that rx is the radio that I need to use to tx as a base, I think this is due to the duplexer being tuned to the rx frequency not the tx frequency, when these duplexers are tuned can the radio's only be used on that frequency only. If any one can help me with this please I would be most grateful, Thanks Lance

May I suggest that you do some homework on how a duplexer works. In the short side of the story, the cans are very frequency sensitive. Moving off the tuned frequency by just a few hundred KHz. will render the new frequency trying to be passed through them unusable.

If your looking to have a base station type of setup, use a single radio with it's own antenna. You might find it much easier to use and requires much less hardware.

Jim

[Bill_G]

Lance - You understand the problem correctly. Because of the duplexer, the TX radio can only TX, and the RX radio can only RX. The duplexer cuts the RX freq to the TX radio rendering it deaf on the rptr input channel. Some RICKs have a third connector you use to interface to a remote control adapter. You set the jumpers to get the correct TX and RX audio paths to that port. Alternately, you plug a mic into the TX radio, set the spkr jumper in the RX radio (15 & 16), and there you have it - a rptr and a base through the duplexer no trouble at all.

[lancerice]

Thanks guys, bill G, that is sort of what I am doing now with the dual antenna setup but I have to use the RX radio to transmit as a base, as if I put the mic in the TX radio I get a horrible sqeeking noise and no voice, but if the repeater cable is unpluged from the TX radio then it works fine, I am a bit confused here, and like I say when I put the duplexer in I can't TX as a base through the RX radio, it will only work as a repeater only?? any ideas with that one if I am making any sence

thanks lance

[Astro Spectra]

What does the ofcom license specify, base or repeater?

[Bill_G]

Thanks guys, bill G, that is sort of what I am doing now with the dual antenna setup but I have to use the RX radio to transmit as a base, as if I put the mic in the TX radio I get a horrible sqeeking noise and no voice, but if the repeater cable is unpluged from the TX radio then it works fine, I am a bit confused here, and like I say when I put the duplexer in I can't TX as a base through the RX radio, it will only work as a repeater only?? any ideas with that one if I am making any sence

thanks lance

How odd. You should be able to plug a mic into the tx radio, and talk on the air while receiving on the rx radio. You should have full duplex. You should be able to drop a rock on the PTT button with your only concern being duty cycle of the xmitter.

No, you cannot xmit on the rx radio on the tx freq. The duplexer will throw it all back at the rfpa with not a watt going to the antenna. Likewise, you cannot receive the rx freq on the tx radio because the duplexer will notch it out. That's what the duplexer does.

Let me play with a repeater I have here, and get back to you.

[Bill_G]

That didn't take long. Two UHF repeaters - one with double Maxtracs, and one with double GM300's, both with the standard RICK and standard notch duplexer - plug a mic in, and I can xmit on the tx freq. Both had no speaker audio on the rx radio. I imagine of I took them apart I'd find the speaker line interrupted in the RICK cable. You need to go back through your setup Lance. I am sure it is simple. Maybe you have the tx and rx cables to the RICK reversed. You will need to connect the spkr jumper in the rcvr cable.

[lancerice]

I have the 2 audio pins soldered together so I can get audio from the radio, but still if I connect a mic to the tx radio with or with out the duplexer it transmits but with a hi pitch sqeel. My repeater cable came from china through ebay, would this make any difference

thanks lance

[lancerice]

one other thing is that I have both the radios programmed the same as if they was to be used on there own, or do I need to have them programmed as a repeater mode in the set up, would this make a difference.
thanks lance

[HLA]

yes it makes a difference, you need to set up the pins accordingly, the tx radio needs to be set up as tx and the rx as rx so the tx radio knows when to keyup

[Bill_G]

I think he's talking about the mobile / repeater mode in the GM300 RSS read / write screens.

Lance - the answer is - no - if you do it right. Repeater mode makes sure you read and program both the tx and rx radios as well as the controller if applicable. It walks you through it and won't let you skip a step. Since you trying for a rather custom setup, it's probably not the way you want to program the radios. You should program them individually.

[lancerice]

if i turn the rx radio off then the tx radio works well, but as soon as i turn the rx radio on it then makes all white noise

[AEC]

I think the biggest hurdle is the radios are REVERSE PROGRAMMED when used in repeater service.

Your transmit is the repeater's RECEIVE freqency, and vice versa..Backward from normal action.

IE:.....

[] zzzz.....TX 468.7625

[/\] Repeater RX 468.7625
TX on 463.7625 zzzz......

RX on 463.7625


- you, the user

[/\] = Repeater station

When you transmit on the repeater's INPUT frequency, you create an audio loop that feeds that audio directly into the receiver that the repeater listens on. This can not be done while the radios are being used AS a repeater.

You transmit on 468.XXXX and the repeater lisens on that frequency.
You listen on 463.XXXX and this is what freqency the repeater transmits back to you, rebroadcasting what you said when you hit the transmit button.

Standing next to the repeater in operation, and you have the 'local' speaker enabled tolisten to traffic, and you then wish to talk THROUGH the repater, you MUST turn DOWN the local speaker, or you will cause the audio loop making the feedback noise.

Remember, the repeater is a BASE RADIO regrammed to repeat the portable radiouser's sifnals with greater power and range, but the repeater is programmed in reverse of 'normal' radios. Using the radios as a base, while leaving the duolexer connected will get you nothing but problems, and ONE radio will be transmitting its power into the other radio, possibly damaging that radio's receiver front end...DON'T DO IT!
Disconnect the 'cans' and program the radios as stand alone units, or use as-is, with one radio left with the speaker 'OFF' .

[lancerice]

i think i might not of explained myself properly, when i tx the tx radio with the rx radio off the tx radio tx's well, if i turn the rx radio on while tx'ing all i get from any other radio is white noise, this is with the speaker on the rx radio off, but if i use the 2 radios as just a repeater then they will work fine. but i am told that I should be able to use the 2 radios as a base or a repeater, i should not get any feedback from speakers as the radios rx and tx different freq's

lance

[Bigred]

i think i might not of explained myself properly, when i tx the tx radio with the rx radio off the tx radio tx's well, if i turn the rx radio on while tx'ing all i get from any other radio is white noise, this is with the speaker on the rx radio off, but if i use the 2 radios as just a repeater then they will work fine. but i am told that I should be able to use the 2 radios as a base or a repeater, i should not get any feedback from speakers as the radios rx and tx different freq's

lance

I would agree. Whether the transmit radio gets its PTT and audio from the repeater controller or the local mic (on the transmit radio) there should be no reaction from from the receive radio. Although the OP states the repeater works, I think not. There must be less than ideal separation between the two radios and the receive radio is barking.

[lancerice]

both the tx radio and the rx radio are one on top of the other, would they need to be seperate then, as most of the repeater setups i have seen are the two radio on top of each other in a casing of some sort, mine are just on the desk top with the duplexer screwed to the wall behind the radios with 12inch patch leads connecting them

lance

[MassFD]

Are you saying the "White Noise" is heard on the local speaker or on the output freq of the TX radio.

If it's on the output freq (you hear it on your portables) you may have an incorrect jumper seting in the GM-300 RX radio. You may be using discriminator audio (which would sound like open squelch) instead of gated audio. With a Rick the audio must ge gated (CSQ/PL) as anything you input to the TX radio will be transmited when you key it up externaly

[lancerice]

the white noise is heard on all mobile's listening to the tx freq of the tx radio when the mic is keyed, not when it is being keyed from another mobile

if you get what i mean??? not very good with my words

[Bill_G]

both the tx radio and the rx radio are one on top of the other, would they need to be seperate then, as most of the repeater setups i have seen are the two radio on top of each other in a casing of some sort, mine are just on the desk top with the duplexer screwed to the wall behind the radios with 12inch patch leads connecting them

lance

By separation he refers to the difference between the transmit and receive frequencies, not the physical space between the radios.

[Bill_G]

the white noise is heard on all mobile's listening to the tx freq of the tx radio when the mic is keyed, not when it is being keyed from another mobile

if you get what i mean??? not very good with my words

You need to change the receive det audio out from unfiltered to gated / filtered. There is a jumper inside the radio that needs to be moved. When you use the set up as a repeater, the transmit radio doesn't come up until it gets a PTT from the COR line line, and since there is receive audio present, that is what gets repeated. But, when you use the mic on the transmit radio, it is in parallel to the unsquelched audio from the rcvr det, and it gets transmitted along with your mic.

[lancerice]

if i change the jumper to filtered will both radio's still be used as a repeater and a base, cause at the moment it is only used as a repeater

[Will]

Yes, Filtered audio is gated by the receiver RUS or un-squelch condition. Usually PL and carrier detect.

To transmit, plug the microphone into the TX radio. And listen to the RX speaker.

[lancerice]

OK, but both the radio's are programed the same so when the tx radio is tx'ing the rx radio will not hear it cause it is listening from a mobile freq not the base/repeater tx freq

[MassFD]

OK, but both the radio's are programed the same so when the tx radio is tx'ing the rx radio will not hear it cause it is listening from a mobile freq not the base/repeater tx freq

That is what you want, you want the RX radio to hear the mobile freq. If it heard the TX freq while you were keing with the local mike you would hear feedback.

Just to clarify, you are leaving the mobiles on the repeater freq (tx high/rxlow) correct? not trying to do simplex

All you are doing localy as a base is using 1 radio (the TX radio) to transmit and the other radio (the RX radio) to receive

Just move the jumper in the RX radio so the output to the rick is muted till a carrier with PL is received and you will be fine.

[lancerice]

where can i find the jumper

[MassFD]

where can i find the jumper

Go to

http://www.repeater-builder.com/motorol ... mpers.html

About 3/8 way down the page find Ju-551 in the photos, it needs to be in position "B"

[lancerice]

Hello, I have changed the jumper and it is working as a base and a repeater very well, but now all the radios that use the repeater sound like they are in a toilet (ehco) when being used as a base rx in normal on rx of all radios and tx to all radios is normal but rx on all radios rxing other radios through repeater are ehcoy, hope this makes sence????

thanks lance

[MassFD]

Could be audio level adjustments in the rick but before you mess with that try this.

When the repeater is active and repeating portable traffic see if the mike you are using on the TX radio is also active.

If the mike is live it may be hearing the RX speaker and repeating it on the air along with the audio from the rick, most GM microphones do not switch the mike elememt only the PTT. I think some of the desk mikes do switch audio so that may be what you need.

[Bill_G]

I like that idea. Good Sherlocking.

[MassFD]

Bill, have had it happen. Took me a while to figure out why I could hear a low band RX on UHF anytime the UHF was repeating. Glad the CDM's have gated audio.

[lancerice]

yep great worked a treat, just turn down the volume on the rx radio and put the mic face down on a rag and the audio between all the mobiles was very clear.
thank you guys

[MassFD]

Glad it worked out, some times it is the little things that trip us up.

By the way the CDM series will not do this as the front and rear connector audio is gated seperatly, the TX will not pass audio from a connector unless the PTT pin makes that connector active. On the GM-300 the front and rear Mike inputs are paraell so any PTT makes them both active at the same time.