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Re: Antenna Advice pse.



    One of the regulars on the Amsat 2m net,  Roy G8GMT, asked  for advice
    on log periodic antennas for analogue satellite working AO27,FO20,FO29
    He is considering a linear polarised  log periodic that covers 2m and 70cms
    in one antenna.

    Non[e] of us on the net have used this type of antenna.  Has anyone got any
    advice, or hints and tips I can pass on.
								[John G7HIA]

That's what i use.  Actually, it's an LPVA, and some of the design concepts
are written up in the current ARRL Antenna Book.  But they talk about an
LPVA as an HF antenna, and as such, SWR is not nearly so critical as it is
at VHF and above.  So i'm not sure i agree with their formulas entirely and
did alot of "cut and try" with NEC2 to come up with what i'm using.  But
mine worked out to be pretty close to 50 ohms direct feed, and without a
diplexer.  I'm still working on refining the design and making sure that it
is reproducible (in currently operating AO-27 with the second prototype and
will be using it for terrestrial purposes for a net tonight, as well).

    A few months ago, I designed and built a 130/1300 MHz log periodic antenna.
    Its a 23 elements, horizontally polarized, 2m boom antenna. It works pretty
    well on all the analog LEOs for elevations lower than 40 degrees.
							[Jean-Louis G/F6AGR]

Mine is only four elements and just covers 2 meters and 70 cm.  I'm hoping 
to pick up 1.2G in a future revision, but that'll probably mean six elements
and alot more experimentation.  The problem i see with a broadbanded approach
is that, in urbanized areas, one may pick up alot of very high power signals
that are already pretty close to the amateur bands.  By having the antenna
performance drop off rapidly away from satellite sub-band means that the
front-end requirements are not quite as stringent.

		     73's and good luck!

			-- KD6PAG  ("Networking Old-Timer, RF newbie")

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