PS: I was wrong once before. I thought I was wrong, but I was wrong - I was
right.
----- Original Message -----
From: "Fred Fillinger" <n3eu@comcast.net>
Subject: Re: Europa-List: Transponder issues
| Fergus Kyle wrote:
| >The only way to increase the radiation is to turn the flat disc
| > of alu into a cone at up to 45deg from the axis of the 'spike'
| > this might tune the antenna more closely to the 50ohm characteristic
| > of cable and spike. You should not have to place the spike on the
| > exterior to improve it.
| > ...
| > PS: - maybe the metal nearby 'blanked' your reply - try changing
| > direction if you get a complaint.
|
| Ferg, I agree with your analysis technically, but FAA requires only
| 125 watts to pass the test, which means their equipment must be able
| to accept some lower output, may be even 50W. The SL-70 puts out
| 250W, not "nominal" but minimum. These things have to 100% reliably
| work in the enroute IFR environment, where in the U.S., at least, they
| have paint you with two radar sites, and one of which can be a
| backstop "super site" in each sector, capable of receiving your
| interrogation at MEAs of only 'bout 3,000' AGL a couple hundred miles
| away, a rather enormous path loss.
|
| Tweaking impedance or radiation pattern I think is unlikely to fix
| anything, especially if ATC can receive your interrogations, under
| that antenna "law of reciprocity" thing!
|
| Reg,
| Fred F.
Beats me, Lieutenant,
Fred,
You de man. I know nothing of the technical side of ATC's
regime, so you are probably right about the power business. Although, I
understood that the average power out was miniscule when the pulse was at
250W minimum but the pulse is very short thus reducing the average.
Otherwise the power output could sterilize us all....... That's the limit of
my ken.
Nevertheless I understood the question to be, "what do I do to
the antenna?" I couldn't see moving it to the belly (outside understood) as
achieving much, whereas revision in situ seemd more efficient - providing as
you say, it is in a proper site/alignment to start with. Also the comment on
'ground plane' seemed ominous.
I concluded that ATC eggheads would have used the same
technology as hams who bounce tiny signals off the moon and catch one
millionth of the outbound signal on return - and these at ATC freqs
(approx). That's 500,000 miles and two atmospheres. I see the loss of signal
due topgraphy but not path length.
You did not comment on directivity/blanking. You don't suppose
those periods of ATC non-reception to be this cause? It seems outlandish but
such things do exist methinks. What would you propose?; I am interested in
your thoughts.............
Cheers, Ferg
|