[Premium-Rx] Broad Bandwidth HF RX Antenna

[Ahmet Gundes]

The best way to come closer to the computer models is to
properly balance "balanced" antennas such as dipoles.

With the exception of Monopoles, most others need to
be properly balanced for predictable results.
In real world, especially with wire antennas,
there are ohmic losses which need to be considered and
higher gauge wire helps.

Shorter antennas are easier to balance. They have lower
gain but better performance as they have less interaction
with surrounding objects.  With Longer/Larger antennas 
getting "lobes" where gain at certain frequencies becomes
directional is not desirable as opposed to a simple Donut
Shape ( or 8 Shape ) response.

I personally think that the BALANCED Antennas will perform
best with lower Noise Floors and much more predictable 
performance. We have done some tests on this and the
results were positive.

One point in balancing antennas. Most commercially available
dipoles and their versions come with BALUNs.
Most "BALUNs" will not work properly unless they are used
properly. BALUNs will only do the job if the input Impedance
is Real and usually in the range of 25 Ohms - 100 Ohms. If the
BALUN sees an impedance other than it is designed for there
are unpredictable results.  

Also, I would like to comment on the NVIS portion of the
email below:
One way to eliminate the NVIS is to use LOOP Antenns. 
There is no NVIS problem with LOOPs.
LOOP antennas are perhaps the easiest antennas to manage with
great performance. LOOP Antennas that have small diameters
are best for receiving systems. Normally 5% diameter or less
for the lowest frequency of reception gives better results
as larger LOOP antennas are no longer Magnetic Field Antennas
and simply the Electric Field influence becomes dominant.
These small LOOP antennas require a low noise AMP to amplify
received signal as they have very low gain due to size. The
LOOPs when design properly and "balanced" correctly will give
incredible performances right out of your shack. I think that
a good receiving system must have 1 Dipole and 1 Loop the least.
LOOPs can be rotated to take advantage of the dips and will
beat dipoles in many cases due to ease of operation.

B. Regards
Ahmet Gundes



> Well it looks like this thread has finally died down, I would like to thank you all for your input on my request for broad bandwidth HF antennas ideas. In a previous job I visited quite a few National Guard facilities and they were all using the B&W T2FD for HF communications. This is what originally got me interested in this antenna for band cruising. I really don't need an antenna that eaks out the last bit of performance for HF receiving purposes due to the high noise floor on the HF bands. I also saw a web site that did extensive modeling of the T2FD and if anything this scared me away from the idea of using it once I saw the analysis, however we all know that what a computer predicts and real world results are often quite different, this is why your input was so important to me. I also like the antenna idea that Al mentioned and to take it one step further I and probably most of you have seen the broadband dipole idea where a separate dipole is cut for each frequency b
 and and they are all attached to a common feed point. My question is has anybody tried this out and how did you like, also has anybody modeled it and what did the feed point impedance look like over frequency? Finally thanks for bringing up the NVIS antenna, it reminded me that I have one packed away somewhere, I think I'll set it up and see how well it works, even if it is a high angle antenna it might work out well for skywave.
>  
> Mark 

>
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