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Roof co-ax amp supply question

Hi All, I want to test out an in-line aerial amp and have supplied it with 12V battery and circuit for testing as below glummed from the web and spares. I can build things but am no shakes on real theory. It works well but seems a bit noisy (hiss on stereo) but I have it down at the RX end of the co-ax at the moment prior to going up the roof with it, so that might make quite a difference to the noise level. Question 1. Does the 22R do anything apart from limiting current to the roof amplifier in emergency (normal operation is about 17mA measured)? Question 2. Are all the values about right for the FM band 70-110 MHz?

The Ae amp is a cheap sealed fully shielded unit really meant for satellite so not probably ideal, but it does cover 5MHz to 2.4GHz and is supposed to have a gain of about 20dB, though using it nearer the lower frequency limit probably less I guess. It also says Return Loss >12.0dB whatever that means!

O----------/\/\22R\/\--------< 12V+ | | / / 3.2mH / | | O

Reply to
Charlie+
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I had rectifier noise on my amplifier's power supply which make a near-stationary glitch on the analogue TV signal. a resistor cured it. I think I used 10 ohms

It may well work better down there.

mine was home-brew from a reproduction of the Phillips OM350 data sheet.

I think that means immunity to signal sent the wrong direction on your cable.

for the inductor I used several turns of solid core telephone wire through a TV antenna balun core.

I probably had too many turns, and saturated the core.

I'd add a creamic capacitor from the top of the inductor to the co-ax shield 100n to 10u should be fine.

--
  When I tried casting out nines I made a hash of it.
Reply to
Jasen Betts

On Fri, 29 Nov 2019 22:51:57 -0000 (UTC), Jasen Betts wrote as underneath :

OK thanks Jasen. I took a look at your OM350 (Italian data) for context. I think I'll do a quick try with a variable R and try out a couple of other values for L and your extra cap idea - just in case any improvement is obvious, good ole 'suck it and see' - thanks for your input. C+

Reply to
Charlie+

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