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Roof co-ax amp supply question

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Charlie+
Guest

Fri Nov 29, 2019 3:01 pm   



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<<Roof Ae+amp -----------||18pF-------->Receiver signal

<<Roof===Co-Ax shield===================>< 0V-

Please excuse crummy drawing!
Thanks C+

Jasen Betts
Guest

Sat Nov 30, 2019 12:51 am   



On 2019-11-29, Charlie+ <charlie_at_xxx.net> wrote:
Quote:
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?


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

Quote:
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 may well work better down there.

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

> It also says Return Loss >12.0dB whatever that means!

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

Quote:

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


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.

Charlie+
Guest

Sat Nov 30, 2019 9:42 am   



On Fri, 29 Nov 2019 22:51:57 -0000 (UTC), Jasen Betts <jasen_at_xnet.co.nz>
wrote as underneath :

Quote:
On 2019-11-29, Charlie+ <charlie_at_xxx.net> wrote:
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?

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

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 may well work better down there.

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

It also says Return Loss >12.0dB whatever that means!

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


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

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.


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+

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