Diathermy was mentioned in the longwire exposure thread and made me think of
this long standing problem here in northern IL..

For some years now, there has been interference on the local 2M repeater
(145.41) which sounds just like the diathermy I used to hear on 10M long
ago. I could tell that it was a crude 60/120Hz. modulated signal which
swept through the repeater input frequency.
It is easily readable on the input over an area at least 3x3 miles. No one
has had the time to spend and I (with some pretty good equip) only went out
a few times (can't spend a lot of time on the way to work... & when I'm
off, it isn't very active), but have limited time as well.

.. It is more active in the morning rush hour and rarely later in the day
and probably never on weekends.


It has to be some kind of RF heating machine, right? Plastic sealing?


Here is a full symptom account to show that I know what characteristics it
has.
I took a spec analyzer out and could see the signal sweeping down at least
five MHz. (where I had it set at the time). I can hear it sweep through
sometimes slowly and sometimes quickly. It so happens that it conveniently
slows down and comes to a stop right around the repeater input - sometimes
ON the input, but spends no more than 2-3 seconds if it happens to stop
there AND stay on long enough. It has a variable time "on"and doesn't
always make it to the input freq.
Now that the repeater is using CTSS full time (last Sept or Oct another
fulltime input spur appeared!) , it doesn't bring up the repeater. However,
you can hear it as it comes into the input across the freq -- if it is
strong enough it will eventually capture and the station talking will go
away, PL detect dies, the beep goes, then this reverses as it continues
through the input freq.

--
Steve N, K,9;d, c. i My email has no u's.

"Steve Nosko" wrote in message
...
Diathermy was mentioned in the longwire exposure thread and made me think
of
this long standing problem here in northern IL..

For some years now, there has been interference on the local 2M repeater
(145.41) which sounds just like the diathermy I used to hear on 10M long
ago. I could tell that it was a crude 60/120Hz. modulated signal which
swept through the repeater input frequency.
It is easily readable on the input over an area at least 3x3 miles. No
one
has had the time to spend and I (with some pretty good equip) only went
out
a few times (can't spend a lot of time on the way to work... & when I'm
off, it isn't very active), but have limited time as well.

. It is more active in the morning rush hour and rarely later in the day
and probably never on weekends.


It has to be some kind of RF heating machine, right? Plastic sealing?


Here is a full symptom account to show that I know what characteristics it
has.
I took a spec analyzer out and could see the signal sweeping down at least
five MHz. (where I had it set at the time). I can hear it sweep through
sometimes slowly and sometimes quickly. It so happens that it
conveniently
slows down and comes to a stop right around the repeater input - sometimes
ON the input, but spends no more than 2-3 seconds if it happens to stop
there AND stay on long enough. It has a variable time "on"and doesn't
always make it to the input freq.
Now that the repeater is using CTSS full time (last Sept or Oct another
fulltime input spur appeared!) , it doesn't bring up the repeater.
However,
you can hear it as it comes into the input across the freq -- if it is
strong enough it will eventually capture and the station talking will go
away, PL detect dies, the beep goes, then this reverses as it continues
through the input freq.

--
Steve N, K,9;d, c. i My email has no u's.



Plastic sealing, using dielectric heating, is often done with the ISM at
27.125 MHz. Loading of the machine might (but isn't supposed to) pull the
frequency. The 5th harmonic is a long way from the 2-meter band, and so is
the 6th. If the RF source is quite close to the repeater, maybe you are
seeing an image response to the 5th harmonic.

You don't need to have a heavy-industrial setting; I once tracked some RF
unhappiness in Milwaukee to a neighborhood shop making vinyl auto tops.

Ed
wb6wsn

"Steve Nosko" wrote in message
...
Diathermy was mentioned in the longwire exposure thread and made me think
of
this long standing problem here in northern IL..

For some years now, there has been interference on the local 2M repeater
(145.41) which sounds just like the diathermy I used to hear on 10M long
ago. I could tell that it was a crude 60/120Hz. modulated signal which
swept through the repeater input frequency.


It could also be a parasitic oscillation in a VHF transmitter as well.
Pager,
police, taxi... Use the spectrum analyzer to see if any nearby activity
jives with the buzzzzzzz.

Pete

Time wise it could be an RF drier for resin.
Lexan for one has to be thoughly dried before molding which would be around
start of the shift. If the top is not fully closed or the electrician has
left the rear panel off then the R.F. would get out. The bottle used has
about 6Kv on it at about .4A so even without an antenna the interference can
be widespread in the area that you mentioned.
Art
"Ed Price" wrote in message
news:jaoXb.72863$fD.59039@fed1read02...

"Steve Nosko" wrote in message
...
Diathermy was mentioned in the longwire exposure thread and made me
think
of
this long standing problem here in northern IL..

For some years now, there has been interference on the local 2M repeater
(145.41) which sounds just like the diathermy I used to hear on 10M long
ago. I could tell that it was a crude 60/120Hz. modulated signal which
swept through the repeater input frequency.
It is easily readable on the input over an area at least 3x3 miles. No
one
has had the time to spend and I (with some pretty good equip) only went
out
a few times (can't spend a lot of time on the way to work... & when I'm
off, it isn't very active), but have limited time as well.

. It is more active in the morning rush hour and rarely later in the
day
and probably never on weekends.


It has to be some kind of RF heating machine, right? Plastic sealing?


Here is a full symptom account to show that I know what characteristics
it
has.
I took a spec analyzer out and could see the signal sweeping down at
least
five MHz. (where I had it set at the time). I can hear it sweep through
sometimes slowly and sometimes quickly. It so happens that it
conveniently
slows down and comes to a stop right around the repeater input -
sometimes
ON the input, but spends no more than 2-3 seconds if it happens to stop
there AND stay on long enough. It has a variable time "on"and doesn't
always make it to the input freq.
Now that the repeater is using CTSS full time (last Sept or Oct another
fulltime input spur appeared!) , it doesn't bring up the repeater.
However,
you can hear it as it comes into the input across the freq -- if it is
strong enough it will eventually capture and the station talking will go
away, PL detect dies, the beep goes, then this reverses as it continues
through the input freq.

--
Steve N, K,9;d, c. i My email has no u's.



Plastic sealing, using dielectric heating, is often done with the ISM at
27.125 MHz. Loading of the machine might (but isn't supposed to) pull the
frequency. The 5th harmonic is a long way from the 2-meter band, and so is
the 6th. If the RF source is quite close to the repeater, maybe you are
seeing an image response to the 5th harmonic.

You don't need to have a heavy-industrial setting; I once tracked some RF
unhappiness in Milwaukee to a neighborhood shop making vinyl auto tops.

Ed
wb6wsn

I can almost echo that experience. Some years ago, while working on an
automated frequency usage project, I noticed a fast drifting signal. It
would key up several repeaters as it drifted through their input
frequencies (in those days of too little use of "PL"). It also caused
havoc with the automated system as it made it appear that frequencies
were being used that were not being used.
I tracked it down to a dispatch transmitter used by a newspaper in
the 170 MHz range. The Motorola people would fix the radio only to have
it start up some time latter. Finally had a scheme where I would call
the radio shop technicians, many of whom were radio amateurs, and say
"guess who is back?"
Because the transmitter's frequency was above most of the Federal
frequencies, guess who it mostly interfered with.
A study a few years latter in a metropolitan area suggested that
oscillating (at an HF rate) of VHF transmitters was much too common.
Since the signals were always drifting, they just presented temporary
interference to any one user who was inclined to pass it off as
just-one-of-those-things.
Be vigilant. The oscillating transmitters are out there. 73 Mac
N8TT

--
J. Mc Laughlin - Michigan USA

"Crazy George" wrote in message
...
Steve:

Sorry to speak of your employer like this, but this is unfortunately a
true
story. I can provide names, dates and times. Doesn't have to be on a
nearby frequency. When Micor series radios were first delivered,
Motorola
told shops not to tune the finals of the base transmitters after
installation (!!!!). There was a brand new Micor high band pager here
which
had a spur on 440 when cold, but not later in the day (sound familiar
yet?).
Drifted through the 440 machine(s) input(s) all morning, buzzing away,
with
also some commercial FM broadcast content also. Two spectrum
analyzers and
3 months were necessary to nail the problem, and a quiet promise to
make
their 400 foot tower about 398 feet shorter one night got them to tune
the
$&*%* thing and fix the problem. They quoted the Motorola directive
to me
when I first contacted them. However, given my reputation, they
believed
the promise and went against Motorola's advice.

--
Crazy George
Remove N O and S P A M imbedded in return address

Mac:

I'm sad to hear that others had to go through the same experience, IIRC,
back in the early 70s. Few labs had spectrum analyzers, and almost no hams
had them, and it was very difficult to find these drifting signals
otherwise. I studied enough of the spectrum to get the idea that the type
acceptance of certain designs should never have been issued. Hopefully all
those transmitters are now defunct.

About the user reactions. Only hams, it seemed, were concerned with
actually finding and getting those problems fixed. As you observe,
commercial users just passed it off, and let the dispatchers suffer. More
ham repeaters were 'open' than commercial, but the interference was there,
nevertheless. The commercial shops found the hams a convenient whipping
boy, blaming them for the various problems. Here, the records I kept
indicated about a 50 to 1 ratio of commercial caused problems to ham caused
problems.

--
Crazy George
Remove N O and S P A M imbedded in return address


"J. McLaughlin" wrote in message
...
I can almost echo that experience. Some years ago, while working on an
automated frequency usage project, I noticed a fast drifting signal. It
would key up several repeaters as it drifted through their input
frequencies (in those days of too little use of "PL"). It also caused
havoc with the automated system as it made it appear that frequencies
were being used that were not being used.
I tracked it down to a dispatch transmitter used by a newspaper in
the 170 MHz range. The Motorola people would fix the radio only to have
it start up some time latter. Finally had a scheme where I would call
the radio shop technicians, many of whom were radio amateurs, and say
"guess who is back?"
Because the transmitter's frequency was above most of the Federal
frequencies, guess who it mostly interfered with.
A study a few years latter in a metropolitan area suggested that
oscillating (at an HF rate) of VHF transmitters was much too common.
Since the signals were always drifting, they just presented temporary
interference to any one user who was inclined to pass it off as
just-one-of-those-things.
Be vigilant. The oscillating transmitters are out there. 73 Mac
N8TT

--
J. Mc Laughlin - Michigan USA

"Crazy George" wrote in message
...
Steve:

Sorry to speak of your employer like this, but this is unfortunately a
true
story. I can provide names, dates and times. Doesn't have to be on a
nearby frequency. When Micor series radios were first delivered,
Motorola
told shops not to tune the finals of the base transmitters after
installation (!!!!). There was a brand new Micor high band pager here
which
had a spur on 440 when cold, but not later in the day (sound familiar
yet?).
Drifted through the 440 machine(s) input(s) all morning, buzzing away,
with
also some commercial FM broadcast content also. Two spectrum
analyzers and
3 months were necessary to nail the problem, and a quiet promise to
make
their 400 foot tower about 398 feet shorter one night got them to tune
the
$&*%* thing and fix the problem. They quoted the Motorola directive
to me
when I first contacted them. However, given my reputation, they
believed
the promise and went against Motorola's advice.

--
Crazy George
Remove N O and S P A M imbedded in return address

"Ed Price" wrote in message
news:jaoXb.72863$fD.59039@fed1read02...
THAT
"Steve Nosko" wrote in message
...
Diathermy was mentioned in the longwire exposure thread and made me
think
of
this long standing problem here in northern IL..

For some years now, there has been interference on the local 2M repeater
(145.41) which sounds just like the diathermy I used to hear on 10M long
ago. [snip]
Steve N, K,9;d, c. i My email has no u's.

[snip] If the RF source is quite close to the repeater, maybe you are
seeing an image response to the 5th harmonic.
wb6wsn

Not an image. Spec analizer and many other receivers hear it, as well
as other repeaters.

Steve

"Steve Nosko" wrote in message
...

"Ed Price" wrote in message
news:jaoXb.72863$fD.59039@fed1read02...
THAT
"Steve Nosko" wrote in message
...
Diathermy was mentioned in the longwire exposure thread and made me
think
of
this long standing problem here in northern IL..

For some years now, there has been interference on the local 2M
repeater
(145.41) which sounds just like the diathermy I used to hear on 10M
long
ago. [snip]
Steve N, K,9;d, c. i My email has no u's.

[snip] If the RF source is quite close to the repeater, maybe you are
seeing an image response to the 5th harmonic.
wb6wsn

Not an image. Spec analizer and many other receivers hear it, as well
as other repeaters.

Steve


Well, if you have that much time to observe the offending signal, start
DF'ing it.

Ed
wb6wsn

Ed:

I think Steve would be interested in hearing a methodology for DFing a
non-stationary signal, as would I. I have tried to track one of these spurs
with a receiver while simultaneously attempting to get a bearing, and gave
up. The Doppler DF systems need it in the passband and frequency stable for
at least one "revolution" of the virtual antenna, which doesn't happen, so
let's hear what works.

--
Crazy George
Remove N O and S P A M imbedded in return address

"Ed Price" wrote in message
news:mXnYb.502$C21.147@fed1read07...

"Steve Nosko" wrote in message
...

"Ed Price" wrote in message
news:jaoXb.72863$fD.59039@fed1read02...
THAT
"Steve Nosko" wrote in message
...
Diathermy was mentioned in the longwire exposure thread and made me
think
of
this long standing problem here in northern IL..

For some years now, there has been interference on the local 2M
repeater
(145.41) which sounds just like the diathermy I used to hear on 10M
long
ago. [snip]
Steve N, K,9;d, c. i My email has no u's.

[snip] If the RF source is quite close to the repeater, maybe you are
seeing an image response to the 5th harmonic.
wb6wsn

Not an image. Spec analizer and many other receivers hear it, as
well
as other repeaters.

Steve


Well, if you have that much time to observe the offending signal, start
DF'ing it.

Ed
wb6wsn

Crazy George wrote:
"I think Steve would be interested in hearing a methodology for DFing a
non-stationary signal, as would I."

Terman says on page 1050 of his 1955 edition:
"The errors in bearing caused by downcoming horizontally polarized sky
waves can be eliminated by replacing the loop antenna with an Adcock
antenna, which in its simplest form consists of two spaced vertical
antennas, connected as shown in Fig. 26-28."

The ARRL Antenna book also gives information and says construction is
not critical.

Best regards, Richard Harrison, KB5WZI