Two radios (same band) to one dual-band antenna

Phillipsc84

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So I know that the obvious setup is a VHF(150) and UHF(450) through a duplexer to a dual band antenna. I have that in the mobile setup and it works great. But in this scenario I have two dual band radios in the same bands and I want to share one antenna for TX and RX. All of the duplexers that I know of are one port VHF and one port UHF. What I need is both radio ports to cover both bands. I would then think multicoupler but only need two ports. I have searched and tried to find an answer and I know it's probably right there but any help would be wonderful.

Thank you to anyone who as an idea.
 

prcguy

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What band do you need both radios on, VHF or UHF? Is there some frequency separation within the single band like one radio on 440 amateur and the other on GMRS or like both on amateur?

So I know that the obvious setup is a VHF(150) and UHF(450) through a duplexer to a dual band antenna. I have that in the mobile setup and it works great. But in this scenario I have two dual band radios in the same bands and I want to share one antenna for TX and RX. All of the duplexers that I know of are one port VHF and one port UHF. What I need is both radio ports to cover both bands. I would then think multicoupler but only need two ports. I have searched and tried to find an answer and I know it's probably right there but any help would be wonderful.

Thank you to anyone who as an idea.
 

Phillipsc84

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They are both 2m/70cm radios. One is a Connect Systems CS800D and the other is an Anytone D578UV. I will use a whole different radio for the GMRS stuff.
 

tweiss3

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That's a bit odd of a setup, using two DMR mobiles on the same antenna. You could always put a coaxial switch in, but you could only use one at a time.

Can you shed light on your intended use and why you need two dualbands running at once?
 

mmckenna

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Yeah, that's not going to work very well.

You would need duplexers for each band, so one for 2 meters, one for 70cm.
They would also be tuned, which means you'd have to have some frequency separation on each band between radios. And depending on the type of duplexer, you'd have to stay within a narrow slice of band for each radio. The duplexers will require tuning by someone with the correct test equipment, cost significantly more than the cost of a second antenna, they'll take up some room, and they will really limit what you can do.

To utilize the full amateur radio 2 meter and 70 centimeter band, you'll need at minimum a dual band antenna for each radio.
 

Phillipsc84

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That's all kind of what I was thinking but wanted to run it past some other great minds. Two antenna's it is. The next thing I need to calculate is the separation for those two, plus a UHF and VHF for commercial bands and a scanner antenna.
 

bharvey2

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Another option might be to use coaxial relays. With those relays, you would disconnect the dormant or non transmitting radio from the antenna while transmitting with the other. It would take a couple of relays and you need to control them, probably via the PTT mic switch. It could get a bit complicated and pricey.
 

mmckenna

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The next thing I need to calculate is the separation for those two, plus a UHF and VHF for commercial bands and a scanner antenna.
As much separation as possible while retaining proper ground planes. The variables are too many to give you a specific distance.
 

dietlein

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If I understand the requirement correctly, you could solve this with a VHF/UHF diplexer followed by two* lumped-element 180° hybrids (one for VHF, one for UHF). Antenna diplexer outputs at the sum ports, termination at the isolated/difference ports, and radios at the other two ports. This will present the proper signals at the "radio ports" on each hybrid, but since the radios don't have separate VHF/UHF connections, you'll need another diplexer per radio.

*Maybe a multi-stage hybrid is possible in order to cover VHF/UHF in one device, but I am not aware of an existing design. It would eliminate both diplexers...
 
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Sounds like you are wanting the functionality of a control station combiner. You occasionally see these used in dispatch centers to interface radios which utilize control station radios (base radios) with nearby systems (such as trunking systems where all the radios in the system constantly transmit and receive on the same frequency). Very lossy, about 10-20 dB IIRC and somewhat pricey ($1200 per 4 resources).

One of my last jobs with a large Motorola dealer was re-designing a dispatch center that was going through a VHF to 7/800 MHz migration. Basically, 6 XTL5000 VHF consolettes were being replaced and two existing 7/800 MHz APX6500 consolettes were being re-used. So, we utilized a 8 channel CSC with 6 new APX8500 consolettes (enabled for VHF and 7/800 MHz) with a triplexer to split VHF and 7/800 MHz into two separate antennas. The downside was we only had about 1/2 W per channel on the output of the CSC (50 W in on VHF).
 

Phillipsc84

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Lots of good info from everyone, thank you!

I'm assuming you want to be able to RX on both radios at the same time?
Yes. Ideally. But at this point it seems like it would make the most send to just run two antennas.

As for the separation question, Once I settle on the antennas I'd like to use I will know more about the gain and total power output so I can get a better calculation on that. I mainly am trying to decide either vertical or horizontal and all that. I'll get more info and see what I can do.
 
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