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Author Topic: 2m affordable solid state repeater ideas?  (Read 765 times)

KB8VUL

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Re: 2m affordable solid state repeater ideas?
« Reply #30 on: June 05, 2022, 04:44:35 PM »

It's ham radio, and you just have to get used to the idea that no one person, and no one use is more important than the other. 

Mark K5LXP
Albuquerque, NM

Yes, you're exactly right.  So if I want to put up a repeater, and another ham has a pair that he's been sitting on for years with no traffic on his repeater, he needs to give that up. That's fair and equal.  Giving HIM preferential treatment because he has the pair and is doing little with it is where the favoritism comes into play.
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K5LXP

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Re: 2m affordable solid state repeater ideas?
« Reply #31 on: June 10, 2022, 09:36:40 AM »

Just saw VUL's post.  The situation suggested is possible but rare at best.  I've been putting up repeaters, both coordinated and uncoordinated in the US and one in Canada since the 1980's.  This is not hard to manage.

Mark K5LXP
Albuquerque, NM
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PE1HZG

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Re: 2m affordable solid state repeater ideas?
« Reply #32 on: June 10, 2022, 12:24:51 PM »

I'm a little worried about the amount of "noise" this thread is attracting.
Let me try to contribute by giving some technical info.

There are a couple of  things you need to consider. First, on 2m, the repeater shift is 600 kHz. That distance is not a lot, and you will need serious, serious filtering to keep transmitter signals out of the receiver. These filters (think of 6, 1m-high coaxial filters) are the majority of your cost, especially if you plan TX and RX to share the same antenna. If your repeater has 10W output (== +40dBm), and given a typical receiver sensitivity of -120dBm, then your filter needs to provide 160dB separation. This is quite a challenge, not just the filters but the shielding of the cabling, ...

Consider that any oscillator doesn't just generate the desired signal, but also a skirt of sideband noise. Part of that noise is in the input frequency of your receiver, and one of the main challenges is to avoid this TX noise from entering your receiver.

In the receiver, you use an oscillator to mix the input signal to, say, 10.7 MHz. Again, the spectral quality of the receiver LO helps to avoid the TX signal, mixed with the sideband noise of the receiver LO, to mix to 10.7 MHz.

A key consideration is that these oscillators must, must have the best, best quality you can afford. Forget about a hamradio-grade radio with a synthesizer; a crystal oscillator has a much higher Q, and hence produces much less sideband noise. So, consider transmitter and receiver with crystal oscillators.
(I know that high-end commercial repeaters exist with synthesizers; the question was "affordable").

The good news is that crystal radios, especially older professional equipment, can be relatively cheap. There is a reason this is mentioned in some of the responses. "sideband noise you don't generate, you don't need to filter". The key is that a weak RX signal should not change if the TX is switched on manually.

Another consideration is thermal cycling. As you know, metals change shape on temperatures. My strong recommendation is to over-over-overdimension the transmitter, so that even after hours of key-down time, the transmitter doesn't get more than hand-warm. Transmitters that get hot do thermal cycling and this will kill your components.

There are sites like www.repeater-builder.com which will provide you hours of reading and insight. This is free, consider you give the website a good study.

Please please resist the temptation to "do features". Making a repeater work well, keeping sensitivity when the TX switches on, and have good, good audio is quite a challenge. Once you got this, you can add pinballmachine features but trust me, you won't be asking questions like this at the skill level once you have your repeater working. Good luck!
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