Hello Folks:

I'm a now somewhat inactive Ham operator, and a couple of days ago received
a call from a colleague at work who is relative newbie to serious SWL'ing.
He was asking for my advice on antennas for his situation. After saving his
pennies for a long time, he finally got his hands on a nice new Icom R-75
and has had after market filters installed ... sorry, can't recall the name
of the filters he mentioned. He has been waiting a long time to get a good
RX, and has been looking forward to finally "hitting the SWL big time" with
a good radio.

Unfortunately, he lives about 600 miles away, and I can't inspect his
installation. Further, I am not at all familiar with the R-75 and it's
capabilities.

He has spent a lot of time on various internet sites after a search for
shortwave antennas and has received glowing recommendations about the
Terminated Folded Dipole, saying it will be the best thing for him since
sliced bread. My experience with a Kenwood TS-870 and Barker & Williamson
TFD at 60 feet was less than impressive compared to a resonant dipole,
except for offering a very flat SWR curve. As would be expected, it stunk
relative to a 4 element Yagi on 20 meters.

Here goes the quick and dirty summary:

1- He lives in a 3 story apartment and has permission to install an antenna
on the rooftop. There are no electrical noise sources on the roof such as
elevators, etc. There would be all the usual noise sources from the interior
of the building like TV's, light dimmers, microwave ovens, etc. As a guess,
the antenna would be about 45 feet above ground, in the center of the roof.

2- He has installed a Terminated Folded Dipole with the center about 20 feet
above the roof, ends droop to about 10 feet above the roof. Feedline is
around 100 feet of 50 ohm coax via a 4 to 1 balun at the feedpoint. I think
he said he was using a carbon terminating resistor around 600 to 800 ohms.

The rooftop is about 300 feet long, by 75 feet wide. Owners of the apartment
are co-operative, but the wire and its supporting structures cannot be
visible from the street.

3- He also has a random length of wire tossed off his balcony on the first
floor up into a tree, about 30 feet away. He used this antenna for several
weeks while he lobbied the building management to allow him to build an
antenna on the roof.

His complaint is that the TFD very rarely outperforms the random wire. Most
of his listening is done below 15 Mhz. He has been told the reason the
antenna may not be performing up to his expectations is the value of the
terminating resistor. I'm not sold on this explanation being the source of
massive levels of performance as yet unlocked in this arrangement.

Based on my experience, my recommendation to him will be to ditch the TFD
and go with a horizontal loop as large as he can possibly make it around, or
near, the circumference of the apartment building roof without being visible
from the ground. As this is a receiving ant, I'd be prone to tell him to
forget about impedance matching between the loop and feedline for the sake
of simplicity, particularly since he wants to do some AM BCB dx'ing and it
is rare to find a balun which would run from the 500 Khz up to 30 Mhz
without substantial roll-off of performance below about 3 Mhz.

I have used many variants of the Horizontal Loop and have always been
impressed with the capture area and relatively low noise pickup. First one
for me was the Loop Skywire, about 15 years ago and there have been many
more since then. This especially true with the AM BCB when I was lucky
enough to have a loop about 1,000 feet long at only about 40 feet average
height above ground.

Any suggestions I could pass along to him which will help him to enjoy the
SWL world? Maybe the R-75 is just such a good radio that the random wire
cannot be substantially improved upon? My "common sense" just tells me this
isn't the case.

Thanks for taking the time to think about this situation a little and pass
along your views on the topic to help this fellow out.

Regards,
Lee Smith
VE4ANC