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(meteorobs) Tamiscaming Response

Hi Steve,

Thanks for the response and comments. Well, even if the visual guys aren't
reading this stuff at least we are. <|:-)

Let me say first of all that I agree that the number of bursts wasn't
spectacular in absolute terms, but as you noted we were using a portable
setup with a small (4-element), commercial FM yagi (i.e. large bandwidth,
low gain) and a portable receiver (Sangean 803A) so I could run everything
off the car battery. So, none of this compares to what you are using. The
antenna I used a few years ago at home was homemade so I could maximize
gain, reduce bandwidth, etc. and it always outperformed this commercial
antenna as well as much larger commercial antennas. However, it isn't even
close to being portable because it uses wide spacing between the elements
and is 6-elements long at 90.7 MHz.

However, the purpose of the project is not to maximize the number of bursts
heard, but one of the purposes is to study the relationship between radio
bursts and visual sightings. As I mentioned in the original message, the
studies done on this (the ones I have seen) have used radar with a
single--or at least close--transmit/receive site. Since most of us (well,
the amateurs among us anyway) don't have access to radar, we have to settle
with either amateur radio techniques or FM broadcasters. And I think that
changes the rules of the game and the outcome. This is what we hope to
resolve.

Also, since we are not necessarily interested in numbers, then radio
frequency doesn't enter the picture from that aspect. It does affect us in
that frequency affects both the amplitude and duration of the bursts. That
aside, it is all irrelevant because the only high-power, 24 hour/day
signals (that we have access to in Waubaushene) are in the FM band and the
TV bands. So, any way you look at it, we are stuck in that frequency range.

Your point about sporadic vs. Orionids is well taken. However, some of the
visual reports here on the list before the peak were fairly high. Also, I
think that the relationship between ZHR as a visual reference and the radio
rate is complex because ZHR implies a single (relatively), fixed direction
and a perfectly transparent, dark sky whereas the peak for radio bursts is
defined in terms of antenna direction. Also, my little antenna has
sidelobes galore--and I'll bet some of them rival the main lobe which means
I'm collecting bursts from lots of directions. And given the azimuth and
elevation of Orion at the time (5 a.m.) pointing the antenna straight up
was a pretty good bet for maximizing bursts. So, I'm not ready to concede
that you are correct, but I'm willing to concede that you're probably
correct that the Orionids didn't substantially affect our numbers.

You mentioned that FM broadcasters aim the signal downwards. While that is
true, no antenna is perfect and the fact that we can hear meteor bursts and
sporadic-E signals indicates that more than enough of the signal is being
sent skyward (or at least toward the horizon).

I know what you are saying about pointing the antenna at 45 deg or at the
horizon, but the antenna elevation angle is irrelevant for sporadic meteors
since by their nature their direction is unpredictable. In fact, it is
irrelevant for showers as well. The main criterion for maximizing signals
is antenna azimuth. The reason for pointing the antenna at the horizon is
to maximize distance between the transmit and receive sites. It does not
maximize signal amplitude, signal duration or number of bursts (see end of
next paragraph). The only question is: Can the transmitting antenna 'see'
the meteor trail and can my receiving antenna 'see' the meteor trail? In
other words: Is the trail close to the transmitting antenna's horizon and
within the beam of my antenna? Since meteor trails at my zenith in
Waubaushen must be at some FM station's horizon (assuming I have chosen an
FM frequency on which there is at least one station within range), then I
will hear bursts.

Beyond the question "Can both the transmitting antenna and the receiving
antenna 'see' the meteor," the main criterion for hearing a meteor burst is
that the signal path obeys the law of specularity (i.e. angle of incidence
equals angle of reflection). That being the case, the only consideration
is: Is there an appropriately oriented meteor within 'sight' of the
antennas to reflect the signal? Any meteor that is tangent to the family of
ellipsoids having the transmit site as one focus and the receive site as
the second focus will provide a signal burst. The location of the meteor
(relative to me) is irrelevant, so it is as likely to be overhead as at 45
deg or at the horizon. (This is another purpose of The Waubaushene
Project--to determine if elevation angle is indeed irrelevant.)

What the elevation angle does affect is the footprint of the reflected
signal. The closer the meteor is to the transmitter, the larger the
footprint. (Conversely, the closer the meteor is to the receiver, the
smaller the footprint.) Whether the footprint size changes enough to make a
substantial difference remains to be seen when we do tests on this later
on. And this may be where pointing the antenna at the horizon makes a
difference to the number of meteor bursts heard since a larger foorprint
may translate to a greater chance of hearing any particular reflection.

Since line-of-sight and specularity are the critera, meteors on the far
side of the transmitting site (relative to me) can also provide signal
bursts. That is, in Waubaushene, I can hear signals from an FM station in
western New York state which have been reflected by a meteor over
Pennsylvania. (I'm north of the FM station; the meteor is south of the FM
station. In other words, the FM station is located between me and the
meteor.) And meteors on the opposite side of me from the transmitting site
can also provide reflections. Therefore, I can hear signals from the New
York station which have been reflected by a meteor over Hudson Bay. (I'm
north of the FM station; the meteor is north of me. In other words, I'm
located between the FM station and the meteor.) This being the case, my
receiving antenna's elevation angle is irrelevant. (There is, by the way, a
limit when I'm pointing my receiving antenna away from the transmitter
because my horizon is well beyond the transmitter's horizon in this case.)
This is the purpose of The Temiscaming project--to demonstrate that you can
receive stations to the south by pointing the antenna north.

[Just to keep out of trouble here, I know that Hudson Bay is too far north,
but I needed a geographical reference in the correct direction that readers
would know.]

Anyway, all that aside, since you commented about the radiation pattern of
FM antennas, maybe you can answer a question for me. Do high-power, coastal
FM stations, such as WYFS (100 kW in Savannah, GA) use directional antennas
to beam the signal inland or do they use omnidirectional antennas and just
accept the loss of signal over the ocean?

Talk to you later.

73,
Phil, VA3ACK
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