[Lf] Re: LF and NB

[Andre Kesteloot]

Paul.Katz at bakerbotts.com wrote:

> I have a Squires-Sanders SS-1R I am interested in using with the LF
> converter featured in QST for April 2002.  The SS-1R has provision for noise
> blanking but I don't have the noise blanker for it.  I was interested in
> adapting your noise blanker to use with the SS-1R.  The SS-1R has a wideband
> IF of 5-5.5 MHz and a blankable IF of 1 MHz.
>
> 73, Paul W5NTQ
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Hello Paul,
Thanks for your interest in the AMRAD LF Up-converter. In our
experience, at LF one of the uppermost noise problems can be
mains-synchronous interference, often produced by light dimmers and
such. These pulses essentially overload the receiver's AGC. Hence one
prefers to get rid of the noise before it enters the receiver, rather
than at the IF level. One way to dispose of this 60HZ QRM is to create
sharp pulses synchronized to the 60 Hz mains. Then, further shaping
circuits allow for (a) adjustable broadening of these pulses and (b)
variable delaying in time. These pulses are then applied to a
double-balanced mixer connected between the antenna and the
up-converter. Looking at the display of the output of the receiver on a
PC screen (using a program such as Spectran or Argo, for instance) it is
now easy to adjust the width and phase of the pulses to ground the
receiver's input during the occurrence of these pulses.

Hope this helps, and good hunting on LF.  
73
André  N4ICK