Topband: how to hear through static crashes?

[Markus Hansen]

With a home brew receiver you can select design features that can mitigate static crashes however there are also ways to help even with a commercial ham receiver such as. 

 1. In my receiver I can adjust the AGC threshold so that loud crashes do not activate the AGC until they become unbearable to listen to.

2.  You can do the same with most commercial receiver by simply turning the RF gain down to a lower level.   Turn the RF gain control down to the point where the S meter no longer (or just barely) moves when listening to your regular back ground noise.  (If the weak station that you are hoping to hear is below the receiver noise level at your QTH then you won't likely hear it will you)

3.  I have found an audio limiter to be very helpful.  With the AGC turn off and/or RF gain turned down, I set the audio limiter so that it limited (clips) any audio output above the level of the weak signal I am listening too.   This protects my ears from excessively loud crashes etc.   I am not aware of any modern receiver that include a AF limiter but the older ARRL Handbooks have circuits for building a simple outboard audio diode limiter.  Just look in the index for "audio limiter/circuit" and you should find a sample.    For the technically minded you can find the limiter I built into my receiver at:     www.ve7ca.net/Hbr200.htm#AudMod

4.  If interference from other stations is not a issue then try the widest IF filter Bandwideth (BW).  When pulse like RF signals (which is basically what lightning crashes are, a series of large RF pules bunched together), go through the  filters in your receiver they are in affect stretched out (see note 1 below) so lightning crashes that you hear will last long going through a very narrow IF CW filters than through the SSB wider filters.  

5.  I have done a considerable amount of experimenting with noise blanking circuits and found that they are not effective with lightning crashes.   Noise Blankers are designed to limit short noise pulses like ignition circuits in the old Volkswagen Bug, lawn mower and in some cases power line leakage that have short duration periods.

6.  By setting the clipping level just above the level of the signal that I am trying to copy, using a wide receiver bandwidth then sometimes I find that Digital Noise Reduction systems help.  I emphasize the word sometimes.  

There my friends are my humble observations.  I sure others will share their experiences to help us all understand and know how to deal with situations like lighting crashes during the summer season.  elay is the average delay time of the energy, the time-domain representation changes and it is not just delayed.  

Note 1.   Not really stretched out, but what is called group delayed.  Group delay is the average delay time of the energy, the time-domain representation changes and it is not just delayed.e  Click on the following URL and you will a visual picture of what happens to a pulse when it goes through a filter:   www.ve7ca.net/Hbr200.htm#FEMixBlnof the energy, the time-domain representation changes and it is not just delayed

Markus Hansen VE7CA
North Vancouver, BC  CANADA
WEB:  ve7ca.net

Markus Hansen VE7CA
North Vancouver, BC  CANADA
WEB:  ve7ca.net






On 2012-03-27, at 8:32 AM, ZR wrote:

> I have found that the cascaded 800Hz mechanical filters in my 75A4 to have 
> less ringing and IMD induced noise than a TS-940 or 950SD with any of the 
> 250, 400, or 500Hz selections.
> 
> Rather than reducing the RF gain pot I use the front end attenuator and have 
> an external one for the A4. None of the above are even close to ideal and 
> each has its better nights.
> 
> Id also suspect the 50-80KHz LC filtering of the vintage boatanchors to be 
> superior but reducing the front end IMD might be a chore without the 
> extensive mods similar to the A4. While my R-4C's had extensive filter, AGC, 
> product detector and audio mods, nothing was done to the front ends and it 
> was never a pleasant radio to use for extended times.....with all its own 
> faults the TS-930 that replaced it was less tiring. For about 6 months I had 
> one of each.
> 
> The NC-300/303 and HQ-170/180 come to mind
> 
> Carl
> KM1H
> 
> 
> ----- Original Message ----- 
> From: "Tree" <tree at kkn.net>
> To: "Robin" <wb6tza at socal.rr.com>
> Cc: "160" <Topband at contesting.com>
> Sent: Tuesday, March 27, 2012 10:15 AM
> Subject: Re: Topband: how to hear through static crashes?
> 
> 
>> For me - Receiver AGC doesn't matter - typically on fast.  However, I will
>> back the RF gain back so that most of the static crashes do not activate
>> the AGC.  I will advance the AF gain to compensate.  I find that setting
>> things up this way allows my brain to focus on the signal without the
>> signal changing amplitude due to the AGC being triggered by a static 
>> crash.
>> 
>> I am not sure IF bandwidth matter that much at this point - but typically
>> use 400 Hz.  I also find a CW tone down around 400 Hz works well for me.
>> 
>> Not sure any digital processing really helps with this - I haven't ever
>> found something that I would say really works.  Diversity seems to help -
>> but only after you are using directive antennas to minimize the static if
>> possible.
>> 
>> I have done this for a very long time - from using an S line on 80 meters
>> at K6RR, to a C line on 160 meters at P40V, a TS850 and K3 here at my
>> station.
>> 
>> Tree N6TR
>> 
>> On Mon, Mar 26, 2012 at 7:57 PM, Robin <wb6tza at socal.rr.com> wrote:
>> 
>>> Maybe this is a good time to share the techniques we individually find
>>> successful for
>>> hearing through the giant sparks.
>>> 
>>> Directional receive antennas, obviously,
>>> 
>>> Receiver AGC?
>>> IF bandwidth?
>>> IF and RF gain distribution? (includes antenna preamps)
>>> what classes of digital processing do better?
>>> what's the best way to keep the receiver processing from ringing and
>>> increasing the
>>> effective duration of the crash?
>>> noise blanker performance?
>>> post receiver audio processing?
>>> can you let the IF strip "clip" in a modern receiver and be an effective
>>> "peak limiter"
>>> without serious ringing?
>>> 
>>> What do YOU do?  and with which receiver?
>>> 
>>> some shared experience might remind all of us of things to try to hear
>>> when the big sparks
>>> are flying
>>> 
>>> Robin, WA6CDR
>>> 
>>> 
>>> 
>>> _______________________________________________
>>> UR RST IS ... ... ..9 QSB QSB - hw? BK
>>> 
>> _______________________________________________
>> UR RST IS ... ... ..9 QSB QSB - hw? BK
>> 
>> 
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> 
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK