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

Folks:

I forgot to mention that he has tried other resistor values, mostly around
the 300 Ohm range.

Also, he's been told that a 9 to 1 balun would also help him out, rather
than the 4 to 1 that he has in place now.

Lee

In article , "Lee Smith" wrote:

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.

Folks:

I forgot to mention that he has tried other resistor values, mostly
around the 300 Ohm range.

Also, he's been told that a 9 to 1 balun would also help him out,
rather than the 4 to 1 that he has in place now.


I suspect the main problem is the 4 to 1 balun. Most units are made for
VHF and start rolling off around 10 MHz. He should try connecting the
coax directly to the TFD and see if this helps. Another tip off would
be the TFD works better on the 31-meter band than the AM broadcast
band.

This may sound silly but often a better low frequency balun will weigh
more so you can get an idea whether it will work at lower frequencies
or not by its heft. The units that have smaller cores rely on other
lightweight elements like capacitors for the impedance conversion and
generally don't work as well at low frequencies.

Another possibility is the coax has a problem causing excessive loss.
Has he sealed the outside end of the coax effectively?

He could also try shorting out the 600 to 800 ohm terminating resistor
making the antenna a folded dipole.

************************************************** ***********
Erecting the horizontal loop at that height should be a very good
performer. Problem with it is picking up noise inside the building
since it looks up and down.

--
Telamon
Ventura, California

In article , "Lee Smith" writes:


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.

This would be my approach as well, making a large horizontal loop, or random
wire, using the circumference of the apartment building roof
, then feed it to the R-75 with some co-ax.

The more antenna exposed to skywaves, the stronger the signal !

I have been thinking about approaching my Co-op board with such a proposal,
but will wait untill they finish installing Lightning Rods & such.

- BTW Art Bell has some Gigunda doouble loop antenna,
wonder how it performs & has he got a QSL from Tibet??

Dan

LS / VE4ANC,

So the TFD set-up as an Inverted "V" is not working and a simple
random wire is giving better performance.

Has he (you) tried posting this question on the Icom R75 eGroup on
YAHOO ?
GoTo= http://groups.yahoo.com/group/icomr75/links

Maybe he should simply consider a simple random wire antenna on the
roof using the Low Noise SWL (Receive Only) Antenna a la John Doty.
* Low Noise (External) Antenna Design presented by John Doty
GoTo= http://www.anarc.org/naswa/badx/ante...e_antenna.html
Build-It-YourSelf and Hear the Difference. From the Association of
North American Radio Clubs (ANARC) WebSite and the Rec.Radio.ShortWave
(NG) WebPage.
He could use his existing Coax and Balun with this Low Noise Antenna.

NOTE: He may have to find a good ground point on the roof and use a
ground radial (counterpoise) on the surface of the roof to get the
most out of any antenna up there.

He (you) may also wish to take a look at the SWL Antennas and AM & FM
Antennas eGroup on YAGOO!
GoTo= http://groups.yahoo.com/group/SWL-AM-FM-Antenna/

Since your interests seem to run to the SkyWire Loop Antenna, you may
wish to consider the newly formed SkyWire Antenna eGroup on YAHOO!
GoTo= http://groups.yahoo.com/group/SkyWires/
For the size of the roof that you have given; a good size SkyWire
Antenna may be the better choice for the roof location. The SkyWire
Antenna could be as little as 8-12 Feet off the surface of the roof
and have an effective heigth of 50 Feet above the ground. Once again,
he could use his existing Coax and Balun with this SkyWire Antenna.
You may wish to suggest that he take a look at the SkyWire Antenna
eGroup on YAHOO: http://groups.yahoo.com/group/SkyWires/



iane ~ RHF
..
..
= = = "Lee Smith"
= = = wrote in message ...
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

BDK,

Based on what you said about the Terminated Folded Dipole (TFD)
Antenna and noting the fact that it is set-up on a Roof in an Inverted
"V" shape.

Then for this TFD Antenna on a questionable Roof surface: A 'good'
Ground Point on the Roof may be required to be able to place Ground
Radials (counterpoise) 'under' the Antenna on the 'surface' of the
Roof to get the most out of any antenna up there on the Roof.


iane ~ RHF
..
..
= = = BDK
= = = wrote in message ...

From the couple of TFD's I have listened on, the TFD's were always
superior side by side with big random wires, slopers, normal dipoles.
Not in signal strenth, but in how quiet they were. Really weak SSB, such
as fishing boats were totally readable on the TFD, but not on any of the
other antennas, there was a lot of noise mixed in, and you could only
copy about half what they were saying even though the S-Meter was
reading another S unit higher.

The Balun is pretty critical.

BDK

Hello All:

Thanks for the verification that my suggestion for a horizontal loop would
be the better system for him.

73 de
Lee VE4ANC

In article , "Lee Smith" wrote:

Hello All:

Thanks for the verification that my suggestion for a horizontal loop would
be the better system for him.


Let us know how things work out for your friend.

--
Telamon
Ventura, California

What kind of roof is this?

If metal, then I'd suggest a vertical, the longer the better (no traps please
!).

At the U of Wis in Milwaukee we had all our antennas up on a 5 story high
concrete/metal roof. A 40 meter ground plane worked extremely well, dipoles
worked great if they were WAY off the roof. Low wires were junk.

jw
wb9uai