[50mhz] Mystery QSB recording of 50.079.96

[Bill VanAlstyne, W5WVO]

Anthony W. DePrato WA4JQS wrote:

> .... then you can look at the peak to peak signal voltage
> of both the suppressed wave and the non suppressed wave.

We need to be careful here.  :-)  We haven't yet determined whether we're
talking about a "suppressed" wave or an "enhanced" wave. Just as a gut reaction,
I'm betting on the latter.

> i would also want to look at the rise and decay times of the signal.

Right. If the decay time (especially) is effectively "instantaneous" (i.e.,
low-millisecond order of magnitude or faster), this would rule out any receiver
AGC involvement.

Just to further hypothesize for a minute --

If it's not propagation (path effect) or the receiver, the only other plausible
explanation for this is an intermittent RF connection at the beacon site that
manifests as degraded antenna coupling. I experienced such a problem on my own
gear last year. It turned out to be a bad coax jumper inside the shack that
would go intermittent when modulated RF of sufficient voltage was applied to it.
(Reducing power past a certain point would make the problem go away.)

In my case, though -- on 6M SSB -- virtually no signal was detectable by a
receiving station when my transmitter's RF path was in this intermittent
degraded state, and to a receiving ham, it sounded just like an intermittent
microphone connector would. Turns out the "on/off" nature of the symptom was due
to the transmitter's SWR foldback protection circuit, which virtually all modern
solid-state transmitters employ. The RF output was basically cut off when the
SWR went high as a result of the intermittent RF connection. It's certainly
possible, however, for the foldback circuit to decrease the transmitter's output
only by some smaller degree. Depends on the worst-case instantaneous SWR caused
by the bad connection and how the transmitter foldback circuit is designed.

If we are looking at an intermittent RF path here, though, I don't think it's
RF-voltage sensitive as mine was, because the mode is CW, not SSB. That means
that the same level of RF voltage is present at the intermittent connection
every time a CW element is transmitted, and one could reasonably assume there
would be some observable correlation between the CW elements and the symptoms.
However, the intermittent signal strength doesn't appear to coincide in any way
with the code elements being sent. I specifically listened for this and, at
least subjectively, didn't hear it. Therefore, I'd more suspect wind creating
the intermittent RF path, if it exists. And that's a hypothesis that could be
tested with further observation.

Might be a good idea at this juncture for somebody to contact the beacon owner
and ask him if there have been any known RF path problems at the site. Ruling
that out, and assuming the recording represents a true enedited profile of the
phenomenon, I don't see any other explanation than some naturally-occuring
propagational process -- like lightning.

Will be very interested in what anyone discovers about this...

Bill / W5WVO


one other
> thing that should be know is lat and long of beacon lat and long of
> each of the two receiveing stations  ant types  and headings at time
> of receiving and types of receivers used. the agc and nb settings
> would be nice to know also. I first thought it was a bad connection
> at the beacon as a quick look at the Scope showed the signal
> decreasing at a contance rate then returning to a constant high
> output. but without spending more time and knowing a few more details
> I am not so sure.
>
>
>> Having said that, I'm unaware of any electromagnetic model that
>> would explain such an interaction between lightning and a signal
>> path -- but then there's a lot of things I'm unaware of.  ;-\
>>
>> Bill / W5WVO
>> DM65
>>
>>
>> Buck - N4PGW wrote:
>>> Could it be receiver desensing? It sounds like a problem I have seen
>>> on 2 meters when I monitor a repeater where the car next to me is
>>> transmitting.
>>>
>>> Buck
>>>
>>>
>>>
>>>
>>>> -----Original Message-----
>>>> From: 50mhz-bounces at mailman.qth.net
>>>> [mailto:50mhz-bounces at mailman.qth.net] On Behalf Of Marvin L. Jones
>>>> Sent: Wednesday, April 27, 2005 1:28 PM
>>>> To: Ken Bessler
>>>> Cc: 50mhz at mailman.qth.net; FT-857 at yahoogroups.com; Dave KC0EMK
>>>> Subject: Re: [50mhz] Mystery QSB recording of 50.079.96
>>>>
>>>> On Wed, 27 Apr 2005, Ken Bessler wrote:
>>>>
>>>>> .............  I've never heard of lightning "helping"
>>>>> a signal before. There was a thunderstorm between my
>>>>> station and the beacon that night.
>>>>
>>>> I _have_ observed lightning enhancing 2M sigs.
>>>> Dunno if it would be effective on 6M, too.
>>>>
>>>> 73
>>>> Jonesy
>>>> --
>>>>   | Marvin L Jones       | jonz         |  W3DHJ   |  linux
>>>>   |  Gunnison, Colorado  |  @           |  Jonesy  |    OS/2     __
>>>>   |   7,703' -- 2,345m   |   config.com |  DM68mn                SK
>>>> Moderator: Ray Brown, KB0STN
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>>>
>>>
>>>
>>> Moderator: Ray Brown, KB0STN
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