InterceptRadio.com Forums

... repeater.
As in buying one, setting it up on one of these hill-tops over here.
Deep cycle, vertical solar, two antennas, etc.
Hidden.
Any thoughts?
Owners?

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If you mean two antennas and no filters ( duplexer ) I doubt you will be happy.
Ya' really need more than 70 to 80 dB ( or more ) isolation to keep the TX out of your RX, at 600 khz offset it is not likely to work well.
That is based on having built and worked on a couple hundred VHF repeaters.
You might get it to work OK, if you stick with old crystal radios like the trusty Micor or MASTR II.
On 440, you can get things to work with separate antennas a bit better.
Then again, what the heck, experiment and see if you get the coverage you want.
Even if you get LOTS of RX desense, if your signal into the "repeater" is strong enuf, it might work.
Pick up a pair of Maxtrac's or something similar, and give it a try.
Lots of info at Repeater-Builder.com

I'm in an isolated area; no interference.
A deep cycle battery, vertical solar panel, two antenna's ( I have a huge 20' vhf Moto for receive) and the box.
I wanna stuff it up on one of the local mountains, cross country style.
I have another local ham with interest.
This would be more experimentation/ hobby.

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This is much easier to do on UHF due to TX/RX split. I got bored one weekend and converted a Motorola Pulsar II mobile phone into a repeater. All it needed was some synthesizer hacking, a squelch, COR, and duplexer retune. For VHF at a minimum you should run a cavity on the RX antenna. One other consideration is running a crossband repeater which some radios can do out of the box.

I want 2 meter due to the popularity.
Thoughts on old school Uniden RX feeding old school vhf TX?
How hard can this be? Rural. Cross country. Hooves.
Ideas?

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OK, here is some of the math and theory to consider.
The common graphs say that at VHF with a 600 khz offset you need 88 dB of isolation between the TX and the RX.
Subtract a few or add a few depending on your situation, quality of the equipment, selectivity of the RX, how clean the TX is, etc. etc.
At around 30 ft of perfect vertical separation you can expect about 55 dB of isolation.
At 150 ft horizontal you might get about the same.
Chances are that you will do better than the graphs and computer programs show.
However, lets say you get 30 ft of vertical, and get better than the theory says of around 55.
You still need around 30 more.
Cut your Tx pwer in half. Now you only need 27.
Cut in half again ( 1/4 power ) still need 24.
Cut again ( 1/8 th ) still need 21.
So, pretty fast even if you drop your planned power out ( whatever that may be ) you get where it is unlikely to work well over just a few milliwatts without some sort of filters.
Even if you are willing to suffer several dB of desense, there is a pretty good chance you will be unhappy with the results. You just won't hear weak stations. The RX will "hear" the weak station and key the TX, the second the TX comes on it "covers up" the weak station, and the TX shuts off. Once the TX is off, the RX hears for just a fraction of a second, and the TX makes it deaf again. So the system just cycles on and off.
A lot of work to have it not come out being useful.
If you use separate antennas, and just a simple notch cavity ( or pass ) in each "leg" it will probably work well enuf.
The issue is that even a very good RX can't hear a weak signal ( say -105 dBM ) in the presence of a +40 dBM ( 10 watts ) transmitter.
So, if you get something like 50 or 60 dB of isolation with separate antennas, and a filter in each feedline for the RX and the TX it will probably work.
Small cavity filters are not that expensive on the used market.
Don't be tricked into buying a mobile notch duplexer for VHF, they need 3 to 5 MHz of offset.
Over the last 40 years, I have tried many of those kind of duplexers to see if I could even re-work one to get them to work at 2 mhz, and none have panned out.
Best thing I have found for small "portable" type two meter repeaters is one of the old TX-RX or WACOM notch duplexers. Small, and BARELY enuf for 600 khz at 10 watts.
But I have seen those kind of dupes for 200 bucks.
Simple 5 inch pass cavities you might even find for 25 bucks each.
5 watts, separate antennas, pair of Maxtrac's back to back.
That would be the way I would do it if I was going to try what you are discussing.
Wouldn't be perfect, but likely to work.

Good info, Thx.
I don't even have a site selected yet.
Idaho 9B shouldn't be to hard.
(9 miles south of BC, 9 miles west of MT)

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Good luck licensing that.

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Interoperability is an attitude, not a technology.

To much involved, not doing.

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