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Two radios on one antenna


tinaeuc
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I’m adding a screen room onto my radio shed and want to have a radio in it.

I don’t want a switch I want to listen on both radios but TX on one at a time.

This is for 2 GMRS radios. Inside will be a BTECH 50x1 and In the screen room will be just the face plat of a Motorola MCS 2000.

Any help would be much appreciated.

Thanks in advance 

update……

I changed my mind and I will only be listening and transmitting on 1 radio at a time.

Thanks for all the help.

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38 minutes ago, tinaeuc said:

Thanks.

If I use a simple T- switch only one radio at a time then I should have no problem?

is there a high end switch with little to no loss?

just for info I’m using 50 foot LMR-400UF and a comet CA-712.

Thanks for your help.

Diamond rates this one at .1 db insertion loss, and 60db of isolation between ports.

https://www.dxengineering.com/parts/dmn-cx210a

I have one on my desk currently; when my faltering btech gets retired, I'm planning to drop it in between the diplexer and my uhf radio, so I can switch between the feed to the dual band ham antenna (comet gp1), and the gmrs antenna (Midland 3db whip)

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I'm going to say, this is possible in a very limited capacity, if you are to use a single SIMPLEX channel on each radio, and they cannot be the same, you could then possibly get a full 6 can duplexer to work. 

 

What you are really looking to do should be done with a single RF deck commercial radio, run dual heads, and enable dual watch/priority watch. 

 

On second though, I found what you are looking for, a T/R switch: https://mfjenterprises.com/products/mfj-1708b-sdr (this one doesn't work well in the UHF commercial band)

You would have to choose which one to use to listen, and the other would be the receive & transmit radio. You CANNOT switch between the two without disconnecting and  reconnecting coax.

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As far as I know, you can't listen on two radios at the same time AND be able to transmit on either of them, one at a time or otherwise.  Even a switch won't make that possible unless you are using two switches to completely cut out the other listening radio before transmitting. 

 

Duplexers are frequency split and directional.  So, that is off the table.

 

Diplexers are also frequency split, but support two-way communications on the same frequency.  However, each side of the split typically has a vast enough frequency split that two radios can't transmit and receive on the same frequency on both sides of the split.  Most of the time, they are band splitters. One side being VHF and the other UHF or one side is VHF/UHF and the other is HF/MF.

 

Some T splitters (which are very affordable), but not all, would allow you to receive on both radios at the same time.  However, you can't transmit without destroying the other listening radio.

 

So, that really only leaves a T connector and two auto-sensing or manual switches.  Keep in mind that there will be a small amount insertion losses, but you are facing potentially high expense. 

 

Frankly, even using 2 high-end auto-sensing switches is risky... I wouldn't do it.

 

Keep in mind, I don't know everything and I am not aware of every device or method out there.  This is just from my experience and training.  Someone else may have a better answer.

 

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1 hour ago, WRHS218 said:

I used one of these, MFJ-1702 2 Position Antenna Switch, for that purpose a long time ago. GigaParts has them for around $40. I am sure there are other brands and venders out there.

Apparently, reading comprehension is not my strong suite. I read the OP's post but didn't recall it long enough to not waste everyone's time. Sorry about that. 

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If you are wanting to have two or more radios on a single antenna you are out of luck..... you need two antenna's one for transmit and one fore receive... If you are willing to run 2 antenna's you can run a control station combiner that allows you to run as many radios as it has ports.  4 is usually the minimum but 8 is more common and they can be expanded to 32 ports which is the largest I have seen. With tow antenna's. 

Now the pricing isn't for the faint of heart, typically about a grand per port on the smaller ones and can get down to 500 per port on the larger units.  Plus of course the two antenna's required.  Signal loss though these is pretty high as well.  Looking at 6 dB both directions.  SO a 50 watt radio will have 12.5 watts out, but it's typical to turn the radios down to 20 watts so you are looking at 5 watts out.  Incoming signal is also 6dB down so you need to be fairly close to the repeaters you are talking to.

 

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7 minutes ago, WRKC935 said:

If you are wanting to have two or more radios on a single antenna you are out of luck..... you need two antenna's one for transmit and one fore receive... If you are willing to run 2 antenna's you can run a control station combiner that allows you to run as many radios as it has ports.  4 is usually the minimum but 8 is more common and they can be expanded to 32 ports which is the largest I have seen. With tow antenna's. 

Now the pricing isn't for the faint of heart, typically about a grand per port on the smaller ones and can get down to 500 per port on the larger units.  Plus of course the two antenna's required.  Signal loss though these is pretty high as well.  Looking at 6 dB both directions.  SO a 50 watt radio will have 12.5 watts out, but it's typical to turn the radios down to 20 watts so you are looking at 5 watts out.  Incoming signal is also 6dB down so you need to be fairly close to the repeaters you are talking to.

 

Thanks.

If I use a simple T- switch only one radio at a time then I should have no problem?

is there a high end switch with little to no loss?

just for info I’m using 50 foot LMR-400UF and a comet CA-712.

Thanks for your help.

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1 hour ago, WRHS218 said:

I used one of these, MFJ-1702 2 Position Antenna Switch, for that purpose a long time ago. GigaParts has them for around $40. I am sure there are other brands and venders out there.

How much loss did you have?

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8 hours ago, tinaeuc said:

I don’t want a switch I want to listen on both radios but TX on one at a time.

I think what you are looking for is what many companies used back in the day and probably still use today. It requires one radio with what they called Remote bases or remotes stations. The picture shown here is called an extended local remote. The draw back is that you cannot generally change the channel in your situation but if you are looking to monitor one repeater or simplex channel, this is about the closest I can come to what you are looking to do. I worked for a newspaper company when I was younger and they had these spread throughout the building for their radio. To the best of my knowledge, they require one radio, not two.

extended local remote.JPG

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17 hours ago, tinaeuc said:

How much loss did you have?

That switch is rated at less than .2 dB insertion loss. We never figured the total loss. The situation we had was we were using a commercial uhf antenna and cable from a older commercial base station install at our plant. We went to a completely different setup but the antenna and cable were left in place. We bought the switch and used it to switch between two personal uhf (non-gmrs) handhelds.  Later we replaced one of the HT's with a scanner and still used the switch. We could find no information on the old cable and antenna though it all worked pretty well. The switch was mounted in the control room.

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Remotes or dual head setup is what you want. In reality you could just put a speaker in one room. Anyway as said you can't have 2 radios able to TX on one antenna without a control station combiner. You could install 2 really good antenna systems for the cost of one control station combiner and not have the 6-12db or more loss. 

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3 hours ago, gortex2 said:

Remotes or dual head setup is what you want. In reality you could just put a speaker in one room. Anyway as said you can't have 2 radios able to TX on one antenna without a control station combiner. You could install 2 really good antenna systems for the cost of one control station combiner and not have the 6-12db or more loss. 

AGREED! A TK-890with dual heads sounds like a good option

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Only issue with dual heads normally are cables between. I have done it as some business's and public safety locations but it can be a challenge. Kenwood was not bad on the 890. I ran the cable thru some 1" conduit being you could tape the plug flat to the cable. The new MSI stuff will go in a 1" conduit also. Again limited to control head cable length but a good option sometimes. Personally at home I have remotes in multiple rooms that I can change channels talk and RX. IP has changed the world in that aspect. 

 

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1 hour ago, tweiss3 said:

Another option, the Vertex VXR-1000 "in car repeater" has Part 95 approval, and you could connect it to the back of your commercial radio's DB9/25 connector and have HT access to your base station throughout the house.

Wasn't aware it had that certification....I have a box of them someplace from an old public safety system. Only drawback is its in band. If your on GMRS CH20 and use a LP CH1 maybe you wont bother the mobile but most in band stuff causes issues. 

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2 minutes ago, gortex2 said:

Wasn't aware it had that certification....I have a box of them someplace from an old public safety system. Only drawback is its in band. If your on GMRS CH20 and use a LP CH1 maybe you wont bother the mobile but most in band stuff causes issues. 

True, but if you turn it down to 1W, and use physical separation of the two RF decks, good commercial equipment should have enough selectivity to have no issues when the VX1000 is on 1-8 and the radio is on 15-22.

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3 hours ago, tweiss3 said:

Another option, the Vertex VXR-1000 "in car repeater" has Part 95 approval, and you could connect it to the back of your commercial radio's DB9/25 connector and have HT access to your base station throughout the house.

Good to know...might have to look for one of those...sounds like it would pair nicely with my setup (previously had crossband set up 1 way for ham, but moved that radio to the truck).

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On 6/15/2022 at 12:17 AM, wayoverthere said:

Diamond rates this one at .1 db insertion loss, and 60db of isolation between ports.

https://www.dxengineering.com/parts/dmn-cx210a

I have one on my desk currently; when my faltering btech gets retired, I'm planning to drop it in between the diplexer and my uhf radio, so I can switch between the feed to the dual band ham antenna (comet gp1), and the gmrs antenna (Midland 3db whip)

Thanks I think this will do.

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On 6/14/2022 at 10:04 PM, tinaeuc said:

I’m adding a screen room onto my radio shed and want to have a radio in it.

I don’t want a switch I want to listen on both radios but TX on one at a time.

This is for 2 GMRS radios. Inside will be a BTECH 50x1 and In the screen room will be just the face plat of a Motorola MCS 2000.

Any help would be much appreciated.

Thanks in advance 

So I had to go with a switch..

only one radio at a time to listen and transmit.

thanks for all the help.

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There a technical solution nobody appears to have mentioned...

However, before wasting your time reading, I believe you simply need to accept the suggestion of a simple antenna switch and one radio at a time.

The technical possibility...

Logically speaking, one probably isn't listening while transmitting.  Can we assume that for now?

If you want to transmit on one radio and have both radios active, a mute switch might do the job, assuming both radios are not on the same frequency.  By 'mute switch', it could be a simple as a pin diode type on the non-transmitting radio that would shunt the antenna input while you are transmitting on the other radio.  This would operate in a similar manner to how many radios work that do not use a relay for TX/RX, except that it would be an external device.

You could have such device on both radios with a bypass switch for use on the chosen active radio.

Couple of issues.
#1. This would likely be a DIY project as I can't recall the last time I've seen and external device like this.
#2. In the bigger picture, this is more complicated and likely far more expensive than a simple antenna switch.


#3. You mentioned a screen room in your shack.  I am assuming you mean an RF shielded room (a.k.a. Faraday Shield) for working on sensitive receiver alignment and such equipment where ambient RF would make such work next to impossible.  Any wiring into the room, including and especially AC power, had to go through a series of RF filters to keep the shielding intact. 

This is a problem for any antenna solution including an A/B switch.

It's a problem because the moment you bring any antenna feed into a screen room, you render the shielding inoperative (defeats the shielding).  It is possible to have an external antenna, but like AC power, it is a specially designed port, usually from the screen room manufacturer that must be capped when not in use. This is, however, yet another expensive option.

 

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