If you're looking for an extremely broadband receive-only antenna, I
highly recommend this active antenna design by PA0RDT. Don't be
dissuaded by the 'whip' antenna reference. The whip is not a whip at
all; rather it is a 2" x 3" (or so) copper foil trace on a pc board
which capacitively couples to the electric field. It's a very
interesting and elegant design that works well, and is easy and
inexpensive to build. It's also -very- stealthy.
http://www.radiopassioni.it/pdf/pa0rdt-Mini-Whip.PDF
... and other useful references are here:
http://carconline.blogspot.com/2009/05/pa0rdt-active-antenna.html
I have built two of them so far. They work very well as half of the
antenna system for diversity reception, and I also use them in
conjunction with the DX Engineering NCC-1 to eliminate local powerline
noise problems which have been particularly severe this Summer due to
the extreme hot weather and lack of rain.
I built mine into a 6" length of 2" i.d.PVC tubing w/ caps on each end,
and so far have just been suspending them from tree branches, but I plan
to put two of them on a PVC boom on the tower to play around with beam
steering via the NCC-1.
73, Dale
WA8SRA
On 8/1/2012 1:55 AM, Brian Lloyd wrote:
On Tue, Jul 31, 2012 at 7:54 PM, George Allen <[email protected]>wrote:
Gerald provides a very interesting discussion of antennas in the
FlexInsider Issue 2; but, what is wrong with just paralleling antennas for
different bands together?
Lets suppose that we wish to monitor both 20 meters and 80 meters at the
same time. If we have two antennas that are resonant respectively on 20
and 80 meters and we parallel them together, the receiving SCU's should be
happy. Yes, even though there is a high impedance for the out-of-resonant
antenna, the receive losses will be low and we will get signals from both
antennas. But, nothing bad should happen.
Why would you assume that the antenna operating out of its normal operating
frequency is high impedance? Remember that the feedline operates as a
transformer and might transform a high-impedance at the antenna into a very
low impedance at the feed-point. What you are suggesting might work in some
instances but it by no means is guaranteed to work in another.
No, if you want multi-band performance you want to use a multi-band antenna
or you want to use a broad-band antenna like a log-periodic or a T2FD.
(http://en.wikipedia.org/wiki/T2FD_Antenna)
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