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VK2ZRG > SETI 09.12.04 20:41l 46 Lines 1868 Bytes #999 (0) @ WW
BID : 983_VK2ZRG
Read: DC5JQ GUEST
Subj: Arecibo @ 440MHz
Path: DB0FHN<DB0THA<DB0ERF<DB0HGW<ON0DXC<ON0RET<DB0RES<ON0BEL<ZL2TZE<VK5UJ<
VK5BRC<VK5ATB<VK2AAB<VK2WI
Sent: 041208/1516Z @:VK2WI.#SYD.NSW.AUS.OC #:56001 [SYDNEY] FBB7 $:983_VK2ZRG
From: VK2ZRG@VK2WI.#SYD.NSW.AUS.OC
To : SETI@WW
VK2ZRG/TPK 1.83d Msg #:983 Date:08-12-04 Time:15:03Z
>R:041206/1913Z @:WT3V.#CNJ.NJ.USA.NA #:32076 [Lakehurst] $:32076_WT3V
Hello Warren and readers,
Warren wrote
>Off the top your "dish gain" figures of 58.8 and 60.4db seem about right
>but still unknown is the gain of the 432MHz antenna itself. I guess we'll
>just have to wait and see if they do any more ham experiments and publish
>the figures again, I forgot where I saw them the first time around.
>In any case just about every ham who ever used 70cM would give his eye
>teeth for that modified Yagi alone and WISH he had a valley to put a
>monster dish in.
Are you suggesting Warren, that there is some magic 70 cm yagi feed
system (at 440 MHz), that somehow increases the gain of Arecibo? If so,
I think that you are mistaken OM. The feed system of a dish antenna must
`illuminate' the entire surface to realise the maximum gain. There must
be a certain `taper' in the feed power to minimise spillover and side lobes.
This is why the 55% efficiency factor applies to dish antennas.
Antennas for space communications must have very low side lobes and
virtually no spillover, to minimise the effective antenna temperature,
-if these antennas are used for RX. If you used a high gain (i.e. narrow
beam width) antenna to illuminate a dish, you would only be using a small
part of the total area of the dish.
So the approximate gain of 60 db at 440 Mhz is THE gain of Arecibo.
There are no magical ways to make it more.
If you know of some magical way to increase the gain, you might be able
to make a fortune with a perpetual motion machine. All hocus pocus stuff
as far as I'm concerned. It would be much easier to make some gold, which
is theoretically possible.
Merry Cricket, Ho Ho Ho
73s from Ralph VK2ZRG@VK2WI.#SYD.NSW.AUS.OC
/ack
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