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Re: QRN RF Limiters Bias question

Hi Leif

QSL. I apologize for the late reply but i have been as usual abroad, with qrl and still am. With my limiters recovery is in about 1 second after the repeater stops TX. The notches are for 144.8 packet radio and work vy well (follow your design) but repeaters are on 145.575-145.775 . So the notches being placed in series now must be retuned, some to remain on 144.8 and some to be on the repeater's frequemncies. I do not know how this combo will work, trying to put the notches in series afterwards. I will try tuning them in a spectrum analyzer of a friend and cascade them and see. The Linrad will do a much much better job on QRN only if 96KHz passband is used, correct? Not just 2.4KHz ...

By the way i found the recordings which u asked me to do some years ago (back then the problem was not as intense as now). Perhaps if u like i could send them to you and could try with Linrad but over a 2.4KHz bandwidth and see what happens with QRN?

Vy 73
Jimmy SV1BTR

----- Original Message -----
From: "Leif Asbrink" <leif@xxxxxxxxxx>
To: "Dimitris Vitorakis" <jimmyv@xxxxxx>
Cc: "Marko Tsekov" <lz2us@xxxxxx>
Sent: Thursday, October 08, 2009 10:38 PM
Subject: Re: QRN RF Limiters Bias question

Hi Jimmy,

thank you very much for your reply. So as to learn more, when you find some time (no rush) i would appreciate if you could elaborate more with a description, in what you write below:

> Another possibillity is to use RF amplifiers without (harmful) capacitors
> that recover immediately after saturation. Then you would not need the
> diode limiters at all.

A big pulse will saturate an amplifier and cause abnormal currents and
perhaps build-up of charges at various points. I can not go through every
possible design mistake, but there is a large number.

What you have to do is to measure the performance bu looking at a steady
carrier while your system is subjected to strong pulses. If the carrier
is not present immediately after the pulse you have a problem.
You would have to investigate DDC voltages to find out what the reason
might be.



PS. Remember that the Linrad noise blanker will do a much better work than a limiter in case you have strong signals in the passband. DS.