(meteorobs) My radio meteor problem

k9gx at thepoint.net k9gx at thepoint.net
Wed Jun 21 18:27:01 EDT 2006


Guys,

This "problem" you are referencing is sporadic E skip. The "tone" you are
hearing is the TV station's video carrier which is amplitude modulated. During
a meteor burst the ionized trail reflects these carrier signals only briefly.
The carriers are always there, you just don't normally have a 
propagation path.
The momentary "ping" you hear during a meteor burst is this carrier signal
reflecting off the ionized trail.

We are in the heart of summertime "sporadic E" season which usually runs from
late May to early July. Es (sporadic E) propagation rarely effects signals
above about 200 Mhz and Es conditions generally present starting at 
frequencies
of about 30 Mhz working up from there. It is not uncommon to hear Es signals
from distant FM broadcast, TV broadcast and amateur stations during Es
openings. The first "hop" is usually 1000-1200 miles. "Double hop" Es skip
normally ranges from 2000-2400 miles.

During a recent weekend the 6m (50 Mhz) amateur band was "open" for me here in
southern Indiana early in the day into Europe and the Caribbean. That 
afternoon
and evening it was open into the Rocky Mountain region first hop and the west
coast 2nd hop. That Sunday Japanese amateurs on 6m contacted stations as far
east as New Mexico and Texas. The amateur 6m band is immediately adjacent to
VHF TV channel 2 at 54-60 Mhz. When 6 is open you'll be seeing distant 
low band
VHF TV stations also.

Another interesting propagation mode is tropo ducting which happens when there
are temperature inversions. Tropo usually presents during early morning and
early evenings as the atmosphere warms or cools at sunrise or sunset. Tropo
conditions present starting at UHF frequencies up around 1 Ghz working
downward. If you're seeing distant UHF TV stations chances are its tropo. The
most intense tropo condition I've seen occurred back in the early 80's. My
radio station's 950 Mhz studio to transmitter link receiver was hearing a 5
watt signal from another station over 200 miles away. That morning the
inversion was especially intense and I was hearing multiple NOAA weather radio
transmitters on each of the 162 Mhz channels. An extremely intense tropo
opening might affect frequencies down to 100 Mhz.

I'm afraid I have some bad news for you. The analog TV signals on low band VHF
channels are going to go away in 2009. FCC is mandating that stations
transition to "HD". The analog signals will be no more.

In case you're wondering I'm a broadcast engineer, amateur radio operator,
meteorob and amateur astronomer.

Regards,

Mark S. Williams
Elizabeth, IN



Quoting Ed Totman <etotman at yahoo.com>:

> I had a problem recently with a constant tone also, on
> a channel 2 offset.  I connected a tv video
> demodulator I recently built to the IF output of my
> radio and was shocked to see and hear channel 2 Kansas
> City, 1500+ miles way!  I couldn't hear any meteors
> but the skip was very interesting.
>
> --- Michael Boschat <aa063 at chebucto.ns.ca> wrote:
>
>> Hi again:
>>
>>  I work on the Channel 6 minus offset of 83.24 Mhz.
>> This morning I went
>> to 83.25 Mhz
>> just to see what it was like, I got a hard "tone"
>> sound. I've heard that
>> before and it
>> is not local, it has to be atmospherics. I remember
>> that tone fading out
>> then coming in
>> strong at other times a few years ago.
>> That is why I went to 83.24 Mhz. On the positive
>> offset of 86.24 Mhz it
>> is similar.
>>
>>  My filter to eliminate other background FM stations
>> ect can be tuned to
>> 63.25 Mhz
>> or Channel 4 thus I could drop lower but I do not
>> have a spectrum
>> analyizer to get the
>> filter tuned right on. I *use* to get the filter
>> tested at the
>> university as they had a rdaio astronomy dept
>> but now that is no more and there is no one here in
>> Halifax has such a
>> device anymore,
>> well, only the TV stations, cable and phone
>> companies...and they do
>> *not* do this for
>> individuals.
>>
>>  So for now, I'll have to hear the static and wait
>> for the atmospherics
>> to go to get the meteor
>> pings.
>>
>> Now, a university station dropped to 88.1 MHz FM at
>> about 25,000 watts.
>> I'm about
>> 1.5 miles from them. Not sure how long they have
>> been at that frequency
>> as I only noticed
>> it 4 days ago.
>>
>>
>> --
>> Clear skies
>> ===========
>> Michael Boschat
>> Royal Astronomical Society of Canada - Halifax
>> Center
>> Astronomy page:  http://www.chebucto.ns.ca/~aa063
>> ---
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