Topband: Switched Delta Pennant
rimradio at direcway.com
Sun Dec 25 03:17:39 EST 2005
Herb, KV4FZ, recently questioned why a 20m bottom fed delta loop he once
had performed as a moderately useful receiving antenna on 160m, and he
noted that the dimensions weren't that different than the delta pennant
described by K6SE. I like playing around with EZNEC so I modeled both
antennas and sent the plots to Herb.
While I was doing so, I wondered what the K6SE delta pennant would look
like if it were fed at the center of the bottom leg instead of at one
corner. The idea was to see whether it would be possible to put a
resistor in both bottom corners and short one or the other with relays
to switch receive directions. It turns out that, at least according to
EZNEC, this should be possible. I had to increase the resistor(s) to
about 1600 ohms from the 950 ohms specified by K6SE, and the "gain"
suffers by about 3db (-38 dbi versus -35 dbi). Otherwise this modified
version would seem to give results very similar to the K6SE design
except with the ability to easily switch directions. EZNEC says both
should have roughly 32 db front-to-back. The feedpoint impedance for
the switched version was about 1200 ohms per the model.
As several topbanders have pointed out, the pennant basically gives a
cardioid pattern with a decent null in one direction but without very
much front-to-side rejection. It won't stack up well against a beverage
or two, but if anyone with space limitations wants to try this out I'd
be willing to pass along the EZNEC plots.
My apologies if this is an old idea already described elsewhere or elsewhen.
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