"Fred Fliss" wrote:
>In reading bits on the web and in the books, it seems the directional
>receive antenna is a necessity. ON4UN's book includes anecdotal examples
>from several lads, which often include comments such as "I switched to the
>40 degree Beverage...". How many Beverages does it take? How do you decide
>which way to aim them?
Remember that John is one of the top DX'ers on 160 and he is talking
about a very high performance station. I think he uses Beverages every
30 degrees but that is obviously out of the question in your case!
>In my acreage-limited existence (less than 1/20th acre), I shall inevitably
>be utilising pennants, ewes, K9AY loops or other such compromise antenna.
>They have wide forward lobes, so there seems not much to worry about there.
>But the nulls in the reverse direction - ah, that must be what is critical!
Not only the nulls but the sidelobes as well. Often you need to
reject noise to one side or the other of the great circle direction and
may want to select a direction which rejects the noise better such
that you improve the S/N. Example...if I wanted to receive FR/F6KDF/T
(about 75 degrees from here) I might need to actually use a 40 degree
Beverage since it would better reject thunderstorm QRN coming from 110
degrees. Of course geomagnetic disturbances also cause the actual
signal path to skew also...sometimes up to 90 degrees in severe storms
(K index of 6 or more).
>I confess that I'm quite challenged here. I really have space for one
>receive antenna, and I am beginning to believe that I shall be forced to
>make it rotary. How many users of small topband receive antennas out there
>find the need to make them rotatable? It occurs to me that will be the only
>way for me to be confident that I can null out QRN, QRM or noise overall.
>At least, until I determine that there is one (or perhaps two) desired
>directions.
Very challenged but both Pennants and shielded loops can be rotated.
>Furthermore, has anybody had experience making the various small receiving
>loops even smaller than suggested in the articles? My highest point in the
>entire antenna farm will be 10 metres high. For me, a receiving antenna
>probably needs to fit in 2.5 X 2.5 meters vertically and horizontally.
>Given appropriate impedance matching and an at-the-antenna preamplifier, are
>they usable at all? Or should I give up and move to Montana where land is
>available for responsible money?
Check out shielded loops...one would easily fit in that area...but it will
not perform as well as a Pennant. If you get really serious, you will
probably be shopping for more real estate!
>Yes, I know if I have said remote preamplifier, I shall need to disable it
>during transmit. I rather expect I shall have to detune my transmit antenna
>(expected to be a shortened, top-loaded vertical) during receive as well.
Correct on both counts!
>Amazing how challenging this technology can be. Not ten years ago I spent
>all my days performing analyses on 40GHz + devices and considered anything
>below 1 GHz to be DC. To find that there are still challenges to be had at
>2 MHz is quite thrilling!
160 is VERY challenging...especially on your small lot. However it can
be done. I have visited many stations in Japan with similar sized lots.
One had a telescoping pole that he could raise to over 25 meters for his
TX antenna. MOST of the JA's do NOT have Beverages because of their space
restrictions and many of those I visited used shielded loops. Just don't
be expecting to hear and work the stations others with more real estate
are using. You can still have a lot of fun on a small lot!
73 & GL!
Bill W4ZV
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