About a month ago I posted a question asking if others had
experienced local FM station interference at various frequencies on
the FRG-100. I finally found the cause and a solution. The FM gets into
the receiver thru the 12V power cable and any other connections to the
receiver (external spkr, tape recorder or computer connection, etc.) IT
DOES NOT ENTER THRU THE ANTENNA; in fact, you can ground the antenna
terminals and it's still there! The FM signal mixes with the 2nd
harmonic of the first local oscillator for some reason, and this allows
either the sum or difference signals of the oscillator's 2nd harmonic
and the FM freq. to fall at various frequencies from 1 to 30 MHz. My
worst were on about 5.06 and 13.1 MHz and this computed out exactly to
two of the local 100 kW FM station frequencies.

The FIX: I was tired of that oddball FRG-100 power connector and the
inability to use a standard 5mm coaxial power connector (common for
most receivers)with the radio on camping DXpeditions so I purchased one
of the standard types from Radio Shack (#274-1582), drilled an
appropriate hole and mounted it just to the left of the existing
connector in the blank spot on the back panel. I then soldered a
small powdered iron torodial filter of about 10 uH between the
connector's + pin and the top edge of the rear fuse holder (remove
fuse first!) I then a soldered a 0.1 uf ceramic capacitor to either
side of the toroid and the other side of the caps to chassis ground
forming a pi filter. I then changed the plug on the power supply 12V
cable to the standard 5mm male coaxial mating plug. The
FM "intermod" is now less than S-2 to S-3 with no external antenna as
long as I don't connect anything else to the accessory jacks on the
receiver's rear panel. Once the antenna is connected, atmospheric noise
or any signal that activates the AGC wipes it out.

I hope this helps some of you that may have this problem. I think the
direct ground connection to the chassis helps the most. The oddball
stock connector connects the power ground to the pc board ground plane
very close to the first mixer. This is probably the cause of the
problem due to common mode ground loop problems in the 100 MHz range.

Frank
K3YAZ

In article .com,
wrote:

About a month ago I posted a question asking if others had
experienced local FM station interference at various frequencies on
the FRG-100. I finally found the cause and a solution. The FM gets
into the receiver thru the 12V power cable and any other connections
to the receiver (external spkr, tape recorder or computer connection,
etc.) IT DOES NOT ENTER THRU THE ANTENNA; in fact, you can ground the
antenna terminals and it's still there! The FM signal mixes with the
2nd harmonic of the first local oscillator for some reason, and this
allows either the sum or difference signals of the oscillator's 2nd
harmonic and the FM freq. to fall at various frequencies from 1 to 30
MHz. My worst were on about 5.06 and 13.1 MHz and this computed out
exactly to two of the local 100 kW FM station frequencies.

The FIX: I was tired of that oddball FRG-100 power connector and the
inability to use a standard 5mm coaxial power connector (common for
most receivers)with the radio on camping DXpeditions so I purchased
one of the standard types from Radio Shack (#274-1582), drilled an
appropriate hole and mounted it just to the left of the existing
connector in the blank spot on the back panel. I then soldered a
small powdered iron torodial filter of about 10 uH between the
connector's + pin and the top edge of the rear fuse holder (remove
fuse first!) I then a soldered a 0.1 uf ceramic capacitor to either
side of the toroid and the other side of the caps to chassis ground
forming a pi filter. I then changed the plug on the power supply 12V
cable to the standard 5mm male coaxial mating plug. The FM "intermod"
is now less than S-2 to S-3 with no external antenna as long as I
don't connect anything else to the accessory jacks on the receiver's
rear panel. Once the antenna is connected, atmospheric noise or any
signal that activates the AGC wipes it out.

I hope this helps some of you that may have this problem. I think the
direct ground connection to the chassis helps the most. The oddball
stock connector connects the power ground to the pc board ground
plane very close to the first mixer. This is probably the cause of
the problem due to common mode ground loop problems in the 100 MHz
range.

Something on the order of 100MHz FM has got to be common mode on the
cables going into the radio. I would expect a common mode choke to work
better than the modification you made. Use just a few widely spaced
turns of the power cord on a ferrite EMI type core should do the trick.
The choke will be more effective on the radio end of the cord in this
case.

--
Telamon
Ventura, California

A McIntosh MR78 can handle that kind of environment. One of the tests that
McIntosh used to do was to inject a 12V interfering signal at a 10MHz offset
to make sure that it didn't cause an increase in distortion at the frequency
of the desired signal. It works very well in the Chicago area. A Luxman
T-110 was also good, as was a Nakamichi Model 430 tuner. There are several
good FM tuners on the market, including the Onkyo units that do the trick.
The early Magnum Dynalab FM tuners that had the discrete front ends were
also pretty good, but some of the models are using one of the Philips auto
radio chipsets, including the RF/Mixer section.
Whereas the FRG100 had those images breaking through on some of the MW
frequencies in my area, the AOR7030 didn't exhibit that characteristic. The
Lowe HF-150 doesn't have this problem either; nor does the Palstar R30. The
latter three units do have a 45MHz 1st I.F.
Nice work, Frank.

Pete

"Stephan Grossklass" wrote in message
...
schrieb:

Believe me this problem drove me crazy for a while. My QTH is
essentially "bathed" in the FM rf from 3 100 kW FM towers that are
within a 6 mile radius and line of sight with the house. This problem
seems to only occur in receivers with a 45MHz 1st IF.

Which would make images from +90 MHz possible, putting you straight into
FMBCB. Signals would only need to find a way around the 30 MHz lowpass
filtering, and there you have it. Your signal levels seem to uncover the
limits of the PCB layout and grounding, pretty hardcore if you ask me.
It would be interesting to know how a '7030 behaves in that kind of
environment. BTW, what kind of FM tuner can handle that kind of "bath"?
It would take at least something along the lines of an Onkyo T-4700, I
assume.

Stephan
--
Home: http://stephan.win31.de/
PC#6: i440BX, 2xP3-500E, 704 MiB, 18+80 GB, R9k AGP 64 MiB, 110W

My FM receivers seem to be OK although one of the stations has an image
due to the signal strength. Both the Palstar R30 and HF-150 that I had
in the past had the same FM pickup problem but it was no where near as
bad as the FRG-100 and it was only on a couple of frequencies if I
remember correctly. The interference could only be detected when the
antenna was disconnected and one manually scanned the bands. By using
the additional connector on the I put on the FRG's back panel along
with some toroidal filters on the 12V power cable I've reduced it to a
tolerable level that only seems to be present if the antenna is
disconnected. I also added a few additional toroids at equal places on
the power cable and that helped even more because they apparently broke
the cable into smaller effective electrical lengths instead of the full
physical length, which is, by the way a half-wavelength in the lower
part of the FM band.

Frank



Pete KE9OA wrote:
A McIntosh MR78 can handle that kind of environment. One of the tests
that
McIntosh used to do was to inject a 12V interfering signal at a 10MHz
offset
to make sure that it didn't cause an increase in distortion at the
frequency
of the desired signal. It works very well in the Chicago area. A
Luxman
T-110 was also good, as was a Nakamichi Model 430 tuner. There are
several
good FM tuners on the market, including the Onkyo units that do the
trick.
The early Magnum Dynalab FM tuners that had the discrete front ends
were
also pretty good, but some of the models are using one of the Philips
auto
radio chipsets, including the RF/Mixer section.
Whereas the FRG100 had those images breaking through on some of the
MW
frequencies in my area, the AOR7030 didn't exhibit that
characteristic. The
Lowe HF-150 doesn't have this problem either; nor does the Palstar
R30. The
latter three units do have a 45MHz 1st I.F.
Nice work, Frank.

Pete

"Stephan Grossklass" wrote in message
...
schrieb:

Believe me this problem drove me crazy for a while. My QTH is
essentially "bathed" in the FM rf from 3 100 kW FM towers that are
within a 6 mile radius and line of sight with the house. This
problem
seems to only occur in receivers with a 45MHz 1st IF.

Which would make images from +90 MHz possible, putting you straight
into
FMBCB. Signals would only need to find a way around the 30 MHz
lowpass
filtering, and there you have it. Your signal levels seem to
uncover the
limits of the PCB layout and grounding, pretty hardcore if you ask
me.
It would be interesting to know how a '7030 behaves in that kind of
environment. BTW, what kind of FM tuner can handle that kind of
"bath"?
It would take at least something along the lines of an Onkyo
T-4700, I
assume.

Stephan
--
Home: http://stephan.win31.de/
PC#6: i440BX, 2xP3-500E, 704 MiB, 18+80 GB, R9k AGP 64 MiB, 110W

That's good...........it sounds like you are really in a strong signal area.
Up here at our new location, things are pretty good. I think that the worst
area in Illinois in in the Barrington area. WBBM, WMAQ, and WGN are so
strong that external mixing spur occur in rusty rain gutters, etc. I realize
that these are MW frequencies we are talking about vs. the FM band image
responses that you are dealing with. As you get higher in frequencies, those
gremlins can become harder to tame.
I've still yet to do your audio mod to my FRG100................too many
receivers. I might be picking up a
McKay-Dymek DR-33. It depends when my friend gets bored with it.

Pete

wrote in message
oups.com...
My FM receivers seem to be OK although one of the stations has an image
due to the signal strength. Both the Palstar R30 and HF-150 that I had
in the past had the same FM pickup problem but it was no where near as
bad as the FRG-100 and it was only on a couple of frequencies if I
remember correctly. The interference could only be detected when the
antenna was disconnected and one manually scanned the bands. By using
the additional connector on the I put on the FRG's back panel along
with some toroidal filters on the 12V power cable I've reduced it to a
tolerable level that only seems to be present if the antenna is
disconnected. I also added a few additional toroids at equal places on
the power cable and that helped even more because they apparently broke
the cable into smaller effective electrical lengths instead of the full
physical length, which is, by the way a half-wavelength in the lower
part of the FM band.

Frank



Pete KE9OA wrote:
A McIntosh MR78 can handle that kind of environment. One of the tests
that
McIntosh used to do was to inject a 12V interfering signal at a 10MHz
offset
to make sure that it didn't cause an increase in distortion at the
frequency
of the desired signal. It works very well in the Chicago area. A
Luxman
T-110 was also good, as was a Nakamichi Model 430 tuner. There are
several
good FM tuners on the market, including the Onkyo units that do the
trick.
The early Magnum Dynalab FM tuners that had the discrete front ends
were
also pretty good, but some of the models are using one of the Philips
auto
radio chipsets, including the RF/Mixer section.
Whereas the FRG100 had those images breaking through on some of the
MW
frequencies in my area, the AOR7030 didn't exhibit that
characteristic. The
Lowe HF-150 doesn't have this problem either; nor does the Palstar
R30. The
latter three units do have a 45MHz 1st I.F.
Nice work, Frank.

Pete

"Stephan Grossklass" wrote in message
...
schrieb:

Believe me this problem drove me crazy for a while. My QTH is
essentially "bathed" in the FM rf from 3 100 kW FM towers that are
within a 6 mile radius and line of sight with the house. This
problem
seems to only occur in receivers with a 45MHz 1st IF.

Which would make images from +90 MHz possible, putting you straight
into
FMBCB. Signals would only need to find a way around the 30 MHz
lowpass
filtering, and there you have it. Your signal levels seem to
uncover the
limits of the PCB layout and grounding, pretty hardcore if you ask
me.
It would be interesting to know how a '7030 behaves in that kind of
environment. BTW, what kind of FM tuner can handle that kind of
"bath"?
It would take at least something along the lines of an Onkyo
T-4700, I
assume.

Stephan
--
Home: http://stephan.win31.de/
PC#6: i440BX, 2xP3-500E, 704 MiB, 18+80 GB, R9k AGP 64 MiB, 110W

Pete - I just had to respond to your comment about the FRG-100 audio
mod. This is the 3rd FRG-100 I've had and it does not have the typical
"muddy" audio and it appears to be totally stock inside. I didn't even
do the mod because it sounds fine as it is. I did change the AM
wiiiiide filter to a more narrow one with better skirts and so far,
other than the input connector mod that's all I've "butchered" on this
100. BTW, I have an older Icom R-72 that I acquired off of Ebay and
it's an excellent receiver in my estimation. No FM problems at all.
Only drawback is they forgot to vent the cabinet!

Frank
K3YAZ
Tucson (where desert wildflowers are everywhere now!)


Pete KE9OA wrote:
That's good...........it sounds like you are really in a strong
signal area.
Up here at our new location, things are pretty good. I think that the
worst
area in Illinois in in the Barrington area. WBBM, WMAQ, and WGN are
so
strong that external mixing spur occur in rusty rain gutters, etc. I
realize
that these are MW frequencies we are talking about vs. the FM band
image
responses that you are dealing with. As you get higher in
frequencies, those
gremlins can become harder to tame.
I've still yet to do your audio mod to my FRG100................too
many
receivers. I might be picking up a
McKay-Dymek DR-33. It depends when my friend gets bored with it.

Pete

wrote in message
oups.com...
My FM receivers seem to be OK although one of the stations has an
image
due to the signal strength. Both the Palstar R30 and HF-150 that I
had
in the past had the same FM pickup problem but it was no where near
as
bad as the FRG-100 and it was only on a couple of frequencies if I
remember correctly. The interference could only be detected when
the
antenna was disconnected and one manually scanned the bands. By
using
the additional connector on the I put on the FRG's back panel along
with some toroidal filters on the 12V power cable I've reduced it
to a
tolerable level that only seems to be present if the antenna is
disconnected. I also added a few additional toroids at equal
places on
the power cable and that helped even more because they apparently
broke
the cable into smaller effective electrical lengths instead of the
full
physical length, which is, by the way a half-wavelength in the
lower
part of the FM band.

Frank



Pete KE9OA wrote:
A McIntosh MR78 can handle that kind of environment. One of the
tests
that
McIntosh used to do was to inject a 12V interfering signal at a
10MHz
offset
to make sure that it didn't cause an increase in distortion at the
frequency
of the desired signal. It works very well in the Chicago area. A
Luxman
T-110 was also good, as was a Nakamichi Model 430 tuner. There are
several
good FM tuners on the market, including the Onkyo units that do
the
trick.
The early Magnum Dynalab FM tuners that had the discrete front
ends
were
also pretty good, but some of the models are using one of the
Philips
auto
radio chipsets, including the RF/Mixer section.
Whereas the FRG100 had those images breaking through on some of
the
MW
frequencies in my area, the AOR7030 didn't exhibit that
characteristic. The
Lowe HF-150 doesn't have this problem either; nor does the Palstar
R30. The
latter three units do have a 45MHz 1st I.F.
Nice work, Frank.

Pete

"Stephan Grossklass" wrote in
message
...
schrieb:

Believe me this problem drove me crazy for a while. My QTH is
essentially "bathed" in the FM rf from 3 100 kW FM towers that
are
within a 6 mile radius and line of sight with the house. This
problem
seems to only occur in receivers with a 45MHz 1st IF.

Which would make images from +90 MHz possible, putting you
straight
into
FMBCB. Signals would only need to find a way around the 30 MHz
lowpass
filtering, and there you have it. Your signal levels seem to
uncover the
limits of the PCB layout and grounding, pretty hardcore if you
ask
me.
It would be interesting to know how a '7030 behaves in that kind
of
environment. BTW, what kind of FM tuner can handle that kind of
"bath"?
It would take at least something along the lines of an Onkyo
T-4700, I
assume.

Stephan
--
Home: http://stephan.win31.de/
PC#6: i440BX, 2xP3-500E, 704 MiB, 18+80 GB, R9k AGP 64 MiB, 110W

Hi Frank,
Mine seemed ok, too. I've got about a 1999 FRG-100B. About
that R-72............maybe the intentionally designed the radio that way, so
it could keep your house warm on those cool desert nights! Just kidding!!!!

Pete

wrote in message
oups.com...
Pete - I just had to respond to your comment about the FRG-100 audio
mod. This is the 3rd FRG-100 I've had and it does not have the typical
"muddy" audio and it appears to be totally stock inside. I didn't even
do the mod because it sounds fine as it is. I did change the AM
wiiiiide filter to a more narrow one with better skirts and so far,
other than the input connector mod that's all I've "butchered" on this
100. BTW, I have an older Icom R-72 that I acquired off of Ebay and
it's an excellent receiver in my estimation. No FM problems at all.
Only drawback is they forgot to vent the cabinet!

Frank
K3YAZ
Tucson (where desert wildflowers are everywhere now!)


Pete KE9OA wrote:
That's good...........it sounds like you are really in a strong
signal area.
Up here at our new location, things are pretty good. I think that the
worst
area in Illinois in in the Barrington area. WBBM, WMAQ, and WGN are
so
strong that external mixing spur occur in rusty rain gutters, etc. I
realize
that these are MW frequencies we are talking about vs. the FM band
image
responses that you are dealing with. As you get higher in
frequencies, those
gremlins can become harder to tame.
I've still yet to do your audio mod to my FRG100................too
many
receivers. I might be picking up a
McKay-Dymek DR-33. It depends when my friend gets bored with it.

Pete

wrote in message
oups.com...
My FM receivers seem to be OK although one of the stations has an
image
due to the signal strength. Both the Palstar R30 and HF-150 that I
had
in the past had the same FM pickup problem but it was no where near
as
bad as the FRG-100 and it was only on a couple of frequencies if I
remember correctly. The interference could only be detected when
the
antenna was disconnected and one manually scanned the bands. By
using
the additional connector on the I put on the FRG's back panel along
with some toroidal filters on the 12V power cable I've reduced it
to a
tolerable level that only seems to be present if the antenna is
disconnected. I also added a few additional toroids at equal
places on
the power cable and that helped even more because they apparently
broke
the cable into smaller effective electrical lengths instead of the
full
physical length, which is, by the way a half-wavelength in the
lower
part of the FM band.

Frank



Pete KE9OA wrote:
A McIntosh MR78 can handle that kind of environment. One of the
tests
that
McIntosh used to do was to inject a 12V interfering signal at a
10MHz
offset
to make sure that it didn't cause an increase in distortion at the
frequency
of the desired signal. It works very well in the Chicago area. A
Luxman
T-110 was also good, as was a Nakamichi Model 430 tuner. There are
several
good FM tuners on the market, including the Onkyo units that do
the
trick.
The early Magnum Dynalab FM tuners that had the discrete front
ends
were
also pretty good, but some of the models are using one of the
Philips
auto
radio chipsets, including the RF/Mixer section.
Whereas the FRG100 had those images breaking through on some of
the
MW
frequencies in my area, the AOR7030 didn't exhibit that
characteristic. The
Lowe HF-150 doesn't have this problem either; nor does the Palstar
R30. The
latter three units do have a 45MHz 1st I.F.
Nice work, Frank.

Pete

"Stephan Grossklass" wrote in
message
...
schrieb:

Believe me this problem drove me crazy for a while. My QTH is
essentially "bathed" in the FM rf from 3 100 kW FM towers that
are
within a 6 mile radius and line of sight with the house. This
problem
seems to only occur in receivers with a 45MHz 1st IF.

Which would make images from +90 MHz possible, putting you
straight
into
FMBCB. Signals would only need to find a way around the 30 MHz
lowpass
filtering, and there you have it. Your signal levels seem to
uncover the
limits of the PCB layout and grounding, pretty hardcore if you
ask
me.
It would be interesting to know how a '7030 behaves in that kind
of
environment. BTW, what kind of FM tuner can handle that kind of
"bath"?
It would take at least something along the lines of an Onkyo
T-4700, I
assume.

Stephan
--
Home: http://stephan.win31.de/
PC#6: i440BX, 2xP3-500E, 704 MiB, 18+80 GB, R9k AGP 64 MiB, 110W