Duplexer with unmatched radios

[WRWE744]

Can I use a duplexer to receive signals on a 5 watt handheld and relay them on a 20 watt mobile?

[SteveShannon]

7 minutes ago, WRWE744 said:

Can I use a duplexer to receive signals on a 5 watt handheld and relay them on a 20 watt mobile?

Technically and very generically, yes. You would connect both radios to the same antenna through the duplexer and to each other through a repeater controller. The repeater controller doesn’t care as long as it gets the signals it needs. 
But you may discover that you have wasted your money. You might find that your receiver desenses or becomes deaf to RF whenever the transmitter is transmitting.

[WRWE744]

Ok, another question. My idea here is a simple relay system that I can put in my car so that when I am outside my car with a 5 watt handheld, I can still hit a repeater through my 20 watt mobile. With that system in mind I think I only need a small antenna on the handheld side of the relay. Is it feasible to use a regular handheld antenna on one side and a separate mobile antenna on the other side, and only use the controller box?

[kmcdonaugh]

10 minutes ago, Sshannon said:

Technically and very generically, yes. You would connect both radios to the same antenna through the duplexer and to each other through a repeater controller. The repeater controller doesn’t care as long as it gets the signals it needs. 
But you may discover that you have wasted your money. You might find that your receiver desenses or becomes deaf to RF whenever the transmitter is transmitting.

This is the correct answer. If you have a long enough cable between the receiver and the transmitter, you may be able to get away with it, but having said that, if you are using a short cable to connect the two, due to most radios having very poor shielding, your transmitter will most likely drown out your receiver, and you will get very poor results.

[WRWE744]

Does this idea work in that scenario?

[WRWE744]

33 minutes ago, WRWE744 said:

Ok, another question. My idea here is a simple relay system that I can put in my car so that when I am outside my car with a 5 watt handheld, I can still hit a repeater through my 20 watt mobile. With that system in mind I think I only need a small antenna on the handheld side of the relay. Is it feasible to use a regular handheld antenna on one side and a separate mobile antenna on the other side, and only use the controller box?

 

Just now, WRWE744 said:

Does this idea work in that scenario?

 

[SteveShannon]

34 minutes ago, WRWE744 said:

Ok, another question. My idea here is a simple relay system that I can put in my car so that when I am outside my car with a 5 watt handheld, I can still hit a repeater through my 20 watt mobile. With that system in mind I think I only need a small antenna on the handheld side of the relay. Is it feasible to use a regular handheld antenna on one side and a separate mobile antenna on the other side, and only use the controller box?

Think about that a little bit.  You would have to transmit on one frequency to the handheld and the mobile would have to transmit on the repeater frequency.  Then, the repeater would transmit any response back to your mobile.  How would you handle that?  Do yo intend the mobile to transmit to the repeater and the repeater to respond to the handheld side of the relay? In that instance it would be immediately retransmitted back to the repeater, causing problems.

Or, do you expect the mobile side of the relay to receive the repeater transmission and then relay it to the transmitter in the handheld side of the relay.  That would require two "relay systems", right?  And you certainly couldn't build this to be full duplex. 

What you propose can be done.  Professional radios in EMS vehicles sometimes provide a relay function to nearby handhelds, but it's not likely it can be easily done for cheap.

[WRWE744]

Ok, thanks for the insight, guys! I'm new to all this and appreciate the help!

[Wrvq441]

I recently tried something similar. My hand held can receive from the repeater just fine, but I am just far enough away from the repeater that I cant transmit to it.

So I had the brilliant brainstorm that I could set my personal repeater to receive from my hand held and transmit to the repeater that I want to use. My hand held would be set to transmit to my personal repeater and to receive from the repeater that I want to use.

My repeater software wouldn’t allow that kind of frequency spread, and it probably wasn’t legal anyway.

I too was spoiled back in the day with EMS where our Pack-Rat hand held would be repeated through our squad radio.

[Lscott]

45 minutes ago, Wrvq441 said:

I recently tried something similar. My hand held can receive from the repeater just fine, but I am just far enough away from the repeater that I cant transmit to it.

So I had the brilliant brainstorm that I could set my personal repeater to receive from my hand held and transmit to the repeater that I want to use. My hand held would be set to transmit to my personal repeater and to receive from the repeater that I want to use.

My repeater software wouldn’t allow that kind of frequency spread, and it probably wasn’t legal anyway.

I too was spoiled back in the day with EMS where our Pack-Rat hand held would be repeated through our squad radio.

That's half duplex operation. Using two separate radios it's possible.  For GMRS the mobile "receiver" radio would be set to one of the simplex channels. The audio output would be connected to the higher power mobile radio set to transmit on the remote repeater's input frequency. As you mentioned the output of the remote repeater would be received directly by the handheld radio. The handheld radio must have ability to be programmed for arbitrary split frequency operation. May of the GMRS specific radios have the frequency split "built in" and only setup for the main repeater channels, which won't work in this case.

You would still need a cavity duplex type filter the same as any other repeater. There are low power ones that would likely work and are tuned by the supplier at purchase. One would end up paying around $100 to $150 depending on model.

https://www.409shop.com/409shop_auctionsearch1.php?userid=100556

Also some type of "controller" would be required to couple the audio from one radio to the other and key it up. One of the Surecom models would likely work.

https://www.409shop.com/409shop_shopcat.php?&usercat=4934&parentid=4934

The advantage to the half duplex idea, if the owner is the only one using it, no ID is required. Every time the handheld radio user ID's the mobile transmitter ID's too. This would NOT be true if it was a full duplex system communicating with a remote repeater. The last point is one of the major issues with full duplex mobile repeaters. It's also a sticking point for Hams using full duplex cross band repeat mode on their mobile radio, which typically don't have a self ID function. Many do it, but it's not strictly legal.

[gortex2]

What you are proposing wont work in GMRS. Its commonly done in the ham community but using different bands. IE uhf portable to mobile then VHF to repeater. A lot of ham rigs actually support this feature. In the LMR field it is done with a DVRS or variety of mobile repeater or extenders. Rarely is the "extender" in the same band. I have a DVRS in my truck and while it was used in the past since I got a BT mic for my mobile 90% of my traffic is on that when outside of the vehicle. 

[KAF6045]

 

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