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Old December 6th 04, 06:45 PM
Ken Bessler
 
Posts: n/a
Default Help w/ QRM mystery

At 29 minutes past the hour on 147.435 simplex
I'm hearing a weak string of 4 DTMF tones. At first
I thought it was someone's remote link but then I
heard this transmission over a much stronger 2m
simplex QSO in progress. There was no hetrodyning
as if 2 signals were coming in at the same freq - the
DTMF string mixed with the S9+60 operator as
if the two signals were mixing with an audio mixer.

I'm convinced that I'm hearing an "image" freq but
from where? My rig is a Kenwood TM-271A with
a 1st IF of 49.95 mhz and a 2nd IF of 450 khz.

I used to know how to rx strong signals outside my
reciever's range by listening to the image but it's
been years and I've forgotten how to do the math.

Is it 2x the 1st IF + the VFO freq? If that's the case,
then the offending signal would be at 247.335 mhz.

Help?

Ken KG0WX




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Old December 6th 04, 07:12 PM
Allodoxaphobia
 
Posts: n/a
Default

On Mon, 6 Dec 2004 11:45:50 -0600, Ken Bessler hath writ:
At 29 minutes past the hour on 147.435 simplex
I'm hearing a weak string of 4 DTMF tones. At first
I thought it was someone's remote link but then I
heard this transmission over a much stronger 2m
simplex QSO in progress. There was no hetrodyning
as if 2 signals were coming in at the same freq - the
DTMF string mixed with the S9+60 operator as
if the two signals were mixing with an audio mixer.

I'm convinced that I'm hearing an "image" freq but
from where? My rig is a Kenwood TM-271A with
a 1st IF of 49.95 mhz and a 2nd IF of 450 khz.

I used to know how to rx strong signals outside my
reciever's range by listening to the image but it's
been years and I've forgotten how to do the math.

Is it 2x the 1st IF + the VFO freq? If that's the case,
then the offending signal would be at 247.335 mhz.

Help?

Ken KG0WX


Yep, you did it right -- if the L.O. is on the high side.
And, it probably is -- with a 49 mcs IF.

Or, "VFO" - (2x 1stIF) = 47.535 mcs. -- if the L.O is on
the low side: 97.485 mcs in this case. (A low side L.O.
could probably be confirmed using a nearby BC FM radio...)

It could also be == 1st IF, too. I.e., a Very Strong
sig on/+/- 49.95 mcs.

But, in both the 47 and the 49 mcs cases, it would need to be
a Very Strong signal to overcome what should be Very Heavy
front end filtering for 1st IF interference in the rig.

Even more frustrating, it could be some combo of inter-mod
with some (also) unknown 3rd freq. (carrier) involved.

Test with a rig with a different 1st IF.

73
Jonesy
--
| Marvin L Jones | jonz | W3DHJ | linux
| Gunnison, Colorado | @ | Jonesy | OS/2 __
| 7,703' -- 2,345m | config.com | DM68mn SK
  #3   Report Post  
Old December 6th 04, 07:12 PM
Allodoxaphobia
 
Posts: n/a
Default

On Mon, 6 Dec 2004 11:45:50 -0600, Ken Bessler hath writ:
At 29 minutes past the hour on 147.435 simplex
I'm hearing a weak string of 4 DTMF tones. At first
I thought it was someone's remote link but then I
heard this transmission over a much stronger 2m
simplex QSO in progress. There was no hetrodyning
as if 2 signals were coming in at the same freq - the
DTMF string mixed with the S9+60 operator as
if the two signals were mixing with an audio mixer.

I'm convinced that I'm hearing an "image" freq but
from where? My rig is a Kenwood TM-271A with
a 1st IF of 49.95 mhz and a 2nd IF of 450 khz.

I used to know how to rx strong signals outside my
reciever's range by listening to the image but it's
been years and I've forgotten how to do the math.

Is it 2x the 1st IF + the VFO freq? If that's the case,
then the offending signal would be at 247.335 mhz.

Help?

Ken KG0WX


Yep, you did it right -- if the L.O. is on the high side.
And, it probably is -- with a 49 mcs IF.

Or, "VFO" - (2x 1stIF) = 47.535 mcs. -- if the L.O is on
the low side: 97.485 mcs in this case. (A low side L.O.
could probably be confirmed using a nearby BC FM radio...)

It could also be == 1st IF, too. I.e., a Very Strong
sig on/+/- 49.95 mcs.

But, in both the 47 and the 49 mcs cases, it would need to be
a Very Strong signal to overcome what should be Very Heavy
front end filtering for 1st IF interference in the rig.

Even more frustrating, it could be some combo of inter-mod
with some (also) unknown 3rd freq. (carrier) involved.

Test with a rig with a different 1st IF.

73
Jonesy
--
| Marvin L Jones | jonz | W3DHJ | linux
| Gunnison, Colorado | @ | Jonesy | OS/2 __
| 7,703' -- 2,345m | config.com | DM68mn SK
  #4   Report Post  
Old December 6th 04, 07:12 PM
Allodoxaphobia
 
Posts: n/a
Default

On Mon, 6 Dec 2004 11:45:50 -0600, Ken Bessler hath writ:
At 29 minutes past the hour on 147.435 simplex
I'm hearing a weak string of 4 DTMF tones. At first
I thought it was someone's remote link but then I
heard this transmission over a much stronger 2m
simplex QSO in progress. There was no hetrodyning
as if 2 signals were coming in at the same freq - the
DTMF string mixed with the S9+60 operator as
if the two signals were mixing with an audio mixer.

I'm convinced that I'm hearing an "image" freq but
from where? My rig is a Kenwood TM-271A with
a 1st IF of 49.95 mhz and a 2nd IF of 450 khz.

I used to know how to rx strong signals outside my
reciever's range by listening to the image but it's
been years and I've forgotten how to do the math.

Is it 2x the 1st IF + the VFO freq? If that's the case,
then the offending signal would be at 247.335 mhz.

Help?

Ken KG0WX


Yep, you did it right -- if the L.O. is on the high side.
And, it probably is -- with a 49 mcs IF.

Or, "VFO" - (2x 1stIF) = 47.535 mcs. -- if the L.O is on
the low side: 97.485 mcs in this case. (A low side L.O.
could probably be confirmed using a nearby BC FM radio...)

It could also be == 1st IF, too. I.e., a Very Strong
sig on/+/- 49.95 mcs.

But, in both the 47 and the 49 mcs cases, it would need to be
a Very Strong signal to overcome what should be Very Heavy
front end filtering for 1st IF interference in the rig.

Even more frustrating, it could be some combo of inter-mod
with some (also) unknown 3rd freq. (carrier) involved.

Test with a rig with a different 1st IF.

73
Jonesy
--
| Marvin L Jones | jonz | W3DHJ | linux
| Gunnison, Colorado | @ | Jonesy | OS/2 __
| 7,703' -- 2,345m | config.com | DM68mn SK
  #5   Report Post  
Old December 7th 04, 04:10 AM
Hamguy
 
Posts: n/a
Default

An Echolink RF node perhaps? Many are ran on simplex frequencies, and a DTMF
code will bring-up the node.



"Allodoxaphobia" wrote in message
...
On Mon, 6 Dec 2004 11:45:50 -0600, Ken Bessler hath writ:
At 29 minutes past the hour on 147.435 simplex
I'm hearing a weak string of 4 DTMF tones. At first
I thought it was someone's remote link but then I
heard this transmission over a much stronger 2m
simplex QSO in progress. There was no hetrodyning
as if 2 signals were coming in at the same freq - the
DTMF string mixed with the S9+60 operator as
if the two signals were mixing with an audio mixer.

I'm convinced that I'm hearing an "image" freq but
from where? My rig is a Kenwood TM-271A with
a 1st IF of 49.95 mhz and a 2nd IF of 450 khz.

I used to know how to rx strong signals outside my
reciever's range by listening to the image but it's
been years and I've forgotten how to do the math.

Is it 2x the 1st IF + the VFO freq? If that's the case,
then the offending signal would be at 247.335 mhz.

Help?

Ken KG0WX


Yep, you did it right -- if the L.O. is on the high side.
And, it probably is -- with a 49 mcs IF.

Or, "VFO" - (2x 1stIF) = 47.535 mcs. -- if the L.O is on
the low side: 97.485 mcs in this case. (A low side L.O.
could probably be confirmed using a nearby BC FM radio...)

It could also be == 1st IF, too. I.e., a Very Strong
sig on/+/- 49.95 mcs.

But, in both the 47 and the 49 mcs cases, it would need to be
a Very Strong signal to overcome what should be Very Heavy
front end filtering for 1st IF interference in the rig.

Even more frustrating, it could be some combo of inter-mod
with some (also) unknown 3rd freq. (carrier) involved.

Test with a rig with a different 1st IF.

73
Jonesy
--
| Marvin L Jones | jonz | W3DHJ | linux
| Gunnison, Colorado | @ | Jonesy | OS/2 __
| 7,703' -- 2,345m | config.com | DM68mn SK





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Old December 7th 04, 04:10 AM
Hamguy
 
Posts: n/a
Default

An Echolink RF node perhaps? Many are ran on simplex frequencies, and a DTMF
code will bring-up the node.



"Allodoxaphobia" wrote in message
...
On Mon, 6 Dec 2004 11:45:50 -0600, Ken Bessler hath writ:
At 29 minutes past the hour on 147.435 simplex
I'm hearing a weak string of 4 DTMF tones. At first
I thought it was someone's remote link but then I
heard this transmission over a much stronger 2m
simplex QSO in progress. There was no hetrodyning
as if 2 signals were coming in at the same freq - the
DTMF string mixed with the S9+60 operator as
if the two signals were mixing with an audio mixer.

I'm convinced that I'm hearing an "image" freq but
from where? My rig is a Kenwood TM-271A with
a 1st IF of 49.95 mhz and a 2nd IF of 450 khz.

I used to know how to rx strong signals outside my
reciever's range by listening to the image but it's
been years and I've forgotten how to do the math.

Is it 2x the 1st IF + the VFO freq? If that's the case,
then the offending signal would be at 247.335 mhz.

Help?

Ken KG0WX


Yep, you did it right -- if the L.O. is on the high side.
And, it probably is -- with a 49 mcs IF.

Or, "VFO" - (2x 1stIF) = 47.535 mcs. -- if the L.O is on
the low side: 97.485 mcs in this case. (A low side L.O.
could probably be confirmed using a nearby BC FM radio...)

It could also be == 1st IF, too. I.e., a Very Strong
sig on/+/- 49.95 mcs.

But, in both the 47 and the 49 mcs cases, it would need to be
a Very Strong signal to overcome what should be Very Heavy
front end filtering for 1st IF interference in the rig.

Even more frustrating, it could be some combo of inter-mod
with some (also) unknown 3rd freq. (carrier) involved.

Test with a rig with a different 1st IF.

73
Jonesy
--
| Marvin L Jones | jonz | W3DHJ | linux
| Gunnison, Colorado | @ | Jonesy | OS/2 __
| 7,703' -- 2,345m | config.com | DM68mn SK



  #7   Report Post  
Old December 7th 04, 04:10 AM
Hamguy
 
Posts: n/a
Default

An Echolink RF node perhaps? Many are ran on simplex frequencies, and a DTMF
code will bring-up the node.



"Allodoxaphobia" wrote in message
...
On Mon, 6 Dec 2004 11:45:50 -0600, Ken Bessler hath writ:
At 29 minutes past the hour on 147.435 simplex
I'm hearing a weak string of 4 DTMF tones. At first
I thought it was someone's remote link but then I
heard this transmission over a much stronger 2m
simplex QSO in progress. There was no hetrodyning
as if 2 signals were coming in at the same freq - the
DTMF string mixed with the S9+60 operator as
if the two signals were mixing with an audio mixer.

I'm convinced that I'm hearing an "image" freq but
from where? My rig is a Kenwood TM-271A with
a 1st IF of 49.95 mhz and a 2nd IF of 450 khz.

I used to know how to rx strong signals outside my
reciever's range by listening to the image but it's
been years and I've forgotten how to do the math.

Is it 2x the 1st IF + the VFO freq? If that's the case,
then the offending signal would be at 247.335 mhz.

Help?

Ken KG0WX


Yep, you did it right -- if the L.O. is on the high side.
And, it probably is -- with a 49 mcs IF.

Or, "VFO" - (2x 1stIF) = 47.535 mcs. -- if the L.O is on
the low side: 97.485 mcs in this case. (A low side L.O.
could probably be confirmed using a nearby BC FM radio...)

It could also be == 1st IF, too. I.e., a Very Strong
sig on/+/- 49.95 mcs.

But, in both the 47 and the 49 mcs cases, it would need to be
a Very Strong signal to overcome what should be Very Heavy
front end filtering for 1st IF interference in the rig.

Even more frustrating, it could be some combo of inter-mod
with some (also) unknown 3rd freq. (carrier) involved.

Test with a rig with a different 1st IF.

73
Jonesy
--
| Marvin L Jones | jonz | W3DHJ | linux
| Gunnison, Colorado | @ | Jonesy | OS/2 __
| 7,703' -- 2,345m | config.com | DM68mn SK





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