Re: QRN RF Limiters Bias question

[hol.gr; jimmyv@xxxxxxxxxxxxxxxx>]

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.
>
> 73
>
> Leif
>
> 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.


LINRADDARNIL