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Re: (meteorobs) Best radio freqs for leonids "observing"
"FM frequencies" can bounce off the moon, but that's not what you're
hearing. This time of year tropospheric ducting (temperature inversions)
cause reflection of VHF signals (this includes "FM frequencies" around
100MHz). Amateurs ("hams") operating on the amateur 2 meter band (144 Mhz)
have recently experienced excellent "tropo" openings from here in the
Southeast. I have a friend who is very active on amateur VHF and he recently
"worked" amateur stations in the northeast, upper midwest and as far west
as Denver on the 2m band with VHF tropo. Broadcast FM antenna systems are
designed to keep signals at a low "angle of radiation" (ie, toward the
horizon).
Moonbounce operation (hams do this also!) on VHF is possible only using
highly directive antenna systems and best conditions are when the moon is at
the horizon. These ham radio antenna systems consist of several stacked yagi
antennas. The same gentleman I refered to above is getting interested in EME
(earth-moon-earth) VHF operation and reported to me just yesterday that he
is hearing European VHF amateurs at his moonrise. He is using a 13 element
2m yagi at 100 ft to receive. The European stations he is hearing are all
using antenna systems as described above and "legal limit" (power in the
1000 watt range). Another important factor to consider is the type of
modulation. Frequency Modulation spreads the signals "energy" over a channel
100khz wide (one FM broadcast channel is as "wide" as 2/3 of the AM
broadcast band). Amateur VHF moonbounce is achieved using CW (morse code).
Energy from these transmissions is 300-500 hertz wide...all the energy is
concentrated at nearly the same frequency. Amateur morse code transmissions
are much more "concentrated" in moonbounce.
I work in the broadcast industry. One of our Florida FM stations was heard
this summer in Italy! However, this signal path was due to "sporadic E"
layer condition. Sporadic E is probably weather related and occurs from late
May through late July here in the northern hemisphere.
Hope this helps clarify what you may be hearing. Sorry, it wasn't
moonbounce.
FYI, I'm a broadcast engineer with an "Extra" class amateur license. I've
been a "ham" for 21 years.
Regards,
Mark
Mark S. Williams
k9gx@n4gn.com
Trustee: KY9IN
Kentuckiana Radiosport Association
Elizabeth, In
EM78ad
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