2 Kenwood TM-V71A for repeater, antenna spacing??

[MrClean]

I have 2 Kenwood TM-V71a radios I'd like to set up a small 2m repeater with..

Receive 2m on unit #1 and then using the 70cm side to transmit (at 5w low) the signal across the house to the 2nd unit in 70cm and then out 2m..

The unit(s) features CW ID'er and remote turn off via DTMF control if needed as well.

I have 2 power supplies and 2 Tram 1181 dual band NMO antennas (with ground plane kits). (UHF is 2.5db gain and VHF is Unity gain). I can change antennas as well to something else.. for this proposed idea I figured I would go small to keep help desense down and these are what I have handy..

I was thinking of setting the 1st unit (RX side) to 5w (irrelevant) and 5w and use the A-B option repeat only (not full crossband repeat)..

The 2nd unit (TX) would be 65 feet away on the opposite side of my house and would be set to 5w (irrelevant) input and then 10w output.

The antennas would also be at opposite ends of the house as well approx 65 feet apart.

Looking at Repeater Builder website it proposes approx 35 db isolation at 60' or so (with 1/2 wave antenna) but I propose using unity/no gain (though based on suggestions here that can change)...

I can put one on the eves at 15ft and the other if need be lower to help with isolation like opposite side and lower height to help block some 'waves'..

And yes, I have checked with the local freq co-coordinator and he gave me some unused pairs to check up here..

Other questions would be:

Using 2 VHF unity gain (1/4) wave antennas (instead of the mixed one above with UHF gain) would that help isolation between 2 antennas?

What if I bought a VHF/UHF signal antenna splitter for the cross house TX/RX and used VHF only antennas outside and small unity UHF's for the UHF TX/RX inside?

What if I bought a single cavity 'notch' filter for like $150-200 set to just my TX (or RX) frequency to help isolation more?

 

[MrClean]

While waiting for a reply to my OP I did some 'road testing' today.

I used a Baofeng 5w HT with one of the Tram 1181 antennas on the roof of my truck (NMO mounted thru roof)..

The single KW 71a was up and running at 10w output with a Comet 2x4SR antenna at the house and a simplex repeater do-dad attached..

I got 19+ miles from the house before the HT wouldn't 'trip' the radio at the house.

 

[Moleculo]

What if I bought a single cavity 'notch' filter for like $150-200 set to just my TX (or RX) frequency to help isolation more?

Adding cavity filter(s) is the best approach for isolation. The other ideas about unity gain antennas might help a little, but not enough to make a big difference. What you want to achieve is something like 80-90db isolation, if possible to avoid de-sensing issues.

I note that you're also kind've doing this whole setup the hard way. You can achieve what you're trying to accomplish with some older motorola (or other) single band radios into an inexpensive notch duplexer with a single antenna.

One idea is Motorola GM300 or similar radios - I even have the motorola repeater interface needed laying around that I would donate to the cause if that is interesting to you. Two radios, the repeater interface, notch duplexer and one antenna and you have a basic repeater.

P.S. I also have 2 Icom VHF notch duplexers that I'm not using - although I'm not "giving" those away

 

[MrClean]

Adding cavity filter(s) is the best approach for isolation. The other ideas about unity gain antennas might help a little, but not enough to make a big difference. What you want to achieve is something like 80-90db isolation, if possible to avoid de-sensing issues.

I note that you're also kind've doing this whole setup the hard way. You can achieve what you're trying to accomplish with some older motorola (or other) single band radios into an inexpensive notch duplexer with a single antenna.

One idea is Motorola GM300 or similar radios - I even have the motorola repeater interface needed laying around that I would donate to the cause if that is interesting to you. Two radios, the repeater interface, notch duplexer and one antenna and you have a basic repeater.

P.S. I also have 2 Icom VHF notch duplexers that I'm not using - although I'm not "giving" those away

I have been looking into GM300 radios since I put this post up. The issue using the cheap $100 China notch duplexers is the tighteset they quote is 3.5 MHz.. They work great for GMRS repeaters and 70cm.