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

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

"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

Actually, if there is an *easy* way, I'd sure like to know!

I started my DF'ing in the Navy in the late 60's, so I'm no slouch.
This is a very sticky problem; few ways to do this. All phase systems
(Doppler, TDOA) require the signal to be well centered in the IF and a well
behaved IF to boot. The amplitude systems (beam, single / dual cardioid)
are better for this, but the sweep-width of this signal makes the beam less
effective due to the change in gain as you get off the design freq.

If I had the time, I'd modify a wide band FM receiver (like a broadcast
receiver 88-108) with a *really* aggressive AFC so it would follow the bogie
along. Then a TDOA should work. Actually any would be better with this
receiver, but I would have to do a little characterization across the
expected freq range first.

I think *any antenna* and a spectrum analyzer watching signal strength is
the best bet...already done some of that. The biggest problem is that it
is most active when we have the least time to hunt.
Steve





"Crazy George" wrote in message
...
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

I can not for the life of me understand why some of you put responses at
the bottom and make one have to scan way down. Leaving that aside, this
is what I did:

I correlated which stations were, and were not, on the air at the
same time as the spurious signal. Then I was able to use the frequency
of the intended frequency to track the offending station. Our DF
capabilities were only good enough to give a sector.
73 Mac N8TT
--
J. Mc Laughlin - Michigan USA

"Crazy George" wrote in message
...
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

"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