[Lowfer] MP, MP, and More MP

[jrusgrove at comcast.net]

JD

Never realized the actual level of static pulses until I obtained a Perseus receiver a couple years 
back. S meters, even bar graph LED types,  generally show some average value of signal level for the 
static pulses. The Perseus ADC 'clip' light catches these fast peaks and lights at a level of -3 dBm 
to warn of ADC overload. During the summer, using band specific dipole antennas, the 'clip' light 
lights routinely on 160 meters and somewhat less frequenctly on 80 meters ... all the while the s 
meter bar graph (even in peak mode) shows the peaks at S9 + 10 or 20. This was a real eye opener and 
caused me to rethink attenuators, preamplifiers, filters, gain distribution and the like. Didn't 
check 500, 185 or 137 kHz  but imagine the situation to be even more of a concern.

Jay


----- Original Message ----- 
From: "JD" <listread at lwca.org>
To: "Discussion of the Lowfer (US, European, &amp;UK) and MedFer bands" <lowfer at mailman.qth.net>
Sent: Friday, October 07, 2011 5:30 AM
Subject: [Lowfer] MP, MP, and More MP


> Was anyone else on air in the vicinity of 137.78 tonight after about 0400,
> or was MP all alone?
>
> After envying all the wonderful screen shots of the past couple of days, I
> ventured out into the field tonight despite severe thunderstorms in the
> western part of the state and a nasty cold storming inside my head.  On the
> plus side, the temperature was pleasant and the tendons I injured in my hand
> last week felt almost human again...but I had to wait until the wind (read:
> blowing dust) died down, which was around 11 PM CDT.  The HiFERs were gone
> by then, I saw no one at all on 495 or 185.3 kHz, and only Mitch seemed to
> be present on 2200 m.
>
> None the less, I used the opportunity to experiment with my clipper circuit
> together with my new antenna buffer amp.  We all know it is possible to have
> too much of a good thing, and that's even true of RF reaching our receivers.
> The buffer has unity voltage gain, but delivers the full open-circuit
> voltage of the antenna to a run of 50 ohm coax and thence to the receiver
> input.  That represents considerable _power_ gain, given the high reactive
> impedance of a 15 meter vertical antenna at LF.  To my surprise, the
> previous mismatch had apparently resulted in over 40 dB of needless
> attenuation at 1750 meters, and even more at 60 kHz.  Remedying that
> mismatch makes it necessary to use the input attenuator from time to time,
> or else the "new, improved" static causes the AGC to modulate the desired
> signal and give it lots of random-ish sidebands.  Without the buffer, the
> static was not bad by previous standards...only up to around S5.  But with
> the buffer, it was between +20 and +30 on peaks tonight, despite the
> considerable distance to the storms.  I found that I get best results with
> static peaking around S9, which seems to be a breakpoint of some sort for
> the AGC time constants in the Kenwood.
>
> During the day, I will stitch together captures illustrating the results and
> try to compress the JPEG enough to pass through the reflector.
>
> Can't wait to try it in the quiet of winter!
>
> John
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