Horrible APRS QRM on 2 Meters

[Richard Beerman-2]

Wonder if anyone else has encountered this on 2 Meters? I am using a 12 ele K1FO yagi - about q12 dB gain on 2. That enters the shack where it is connected to a Downeast Microwave 50 Watt transverter with about 17 dB gain on receive. The output of the transverter is connected to transverter input on my old K-3. For the longest time, I was receiving loud QRM from what I initially thought were power line noise bursts. But, I became suspicious because these bursts were about a second or so in duration consistently. During this time, I was testing my setup for meteor scatter using the MSK 144 software found in the current WSJT-X suite. These loud bursts created huge red images on the monitor watching in 144.150 MHz, the MSK144 calling frequency.

I got suspicious that these signals were not simple electrical pole shorting noise. So, I connected a whip to my old TS-790S rig and tuned it to 144.390 MHz, the North American APRS frequency.  WALAAAAA, the signals on my monitor connected to a K-3 tuned to 144.150 MHz corresponded perfectly to the WPRS signals on 144.390 MHz, some 240 kHz away! The preamp on the K-3 was off. There were no other receiving preamps in line at the time. Later, I turned on an external 2 Meter preamp and all that happened was that the APRS signals were larger at 144.150 MHz.

It appears that the front end of my K-3 simply folds up in the presence of strong signals that are WAY off the receiving frequency. I can tell you that connecting the same antenna/transverter to a Kenwood TS 590SG, there were no traces of the APRS signals. And connecting the TS-790S to the K1FO likewise produced no APRS QRM at 144.150. To me, with the presence of a number of strong APRS signals on 144.390 makes this K-3 extremely unusable on 2 Meters. I was running the K-3 noise blanker to handle the rest of the noise here but likewise, I also had noise blankers running on the two Kenwood radios as well.

Any suggestions are welcome.  Dick  W5AK  
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[wayne burdick]

Dick,

Just to make sure I understand: are you using the K3 as an IF? If so, what band -- 10 meters?

It makes no sense that the K3 would have difficulty with out of band signals in the manner you describe. It has far better dynamic range on all bands, including 10 meters, than the TS-590.

Wayne
N6KR


> On Jul 27, 2018, at 6:59 PM, Richard Beerman <[hidden email]> wrote:
>
> Wonder if anyone else has encountered this on 2 Meters? I am using a 12 ele K1FO yagi - about q12 dB gain on 2. That enters the shack where it is connected to a Downeast Microwave 50 Watt transverter with about 17 dB gain on receive. The output of the transverter is connected to transverter input on my old K-3. For the longest time, I was receiving loud QRM from what I initially thought were power line noise bursts. But, I became suspicious because these bursts were about a second or so in duration consistently. During this time, I was testing my setup for meteor scatter using the MSK 144 software found in the current WSJT-X suite. These loud bursts created huge red images on the monitor watching in 144.150 MHz, the MSK144 calling frequency.
>
> I got suspicious that these signals were not simple electrical pole shorting noise. So, I connected a whip to my old TS-790S rig and tuned it to 144.390 MHz, the North American APRS frequency.  WALAAAAA, the signals on my monitor connected to a K-3 tuned to 144.150 MHz corresponded perfectly to the WPRS signals on 144.390 MHz, some 240 kHz away! The preamp on the K-3 was off. There were no other receiving preamps in line at the time. Later, I turned on an external 2 Meter preamp and all that happened was that the APRS signals were larger at 144.150 MHz.
>
> It appears that the front end of my K-3 simply folds up in the presence of strong signals that are WAY off the receiving frequency. I can tell you that connecting the same antenna/transverter to a Kenwood TS 590SG, there were no traces of the APRS signals. And connecting the TS-790S to the K1FO likewise produced no APRS QRM at 144.150. To me, with the presence of a number of strong APRS signals on 144.390 makes this K-3 extremely unusable on 2 Meters. I was running the K-3 noise blanker to handle the rest of the noise here but likewise, I also had noise blankers running on the two Kenwood radios as well.
>
> Any suggestions are welcome.  Dick  W5AK  



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[wayne burdick]

Another thought: The K3 has two noise blankers. The hardware blanker does see a broad input frequency range (so it can suppress very fast-rise-time noise pulses), and as with similar blankers, you have to keep the NB threshold high enough to not cause intermod.

Try using just the DSP blanker, which is post-crystal-filter. Or a touch of each. This can be very effective on disparate noise sources.

Wayne

> On Jul 27, 2018, at 6:59 PM, Richard Beerman <[hidden email]> wrote:
>
> Wonder if anyone else has encountered this on 2 Meters? I am using a 12 ele K1FO yagi - about q12 dB gain on 2. That enters the shack where it is connected to a Downeast Microwave 50 Watt transverter with about 17 dB gain on receive. The output of the transverter is connected to transverter input on my old K-3. For the longest time, I was receiving loud QRM from what I initially thought were power line noise bursts. But, I became suspicious because these bursts were about a second or so in duration consistently. During this time, I was testing my setup for meteor scatter using the MSK 144 software found in the current WSJT-X suite. These loud bursts created huge red images on the monitor watching in 144.150 MHz, the MSK144 calling frequency.
>
> I got suspicious that these signals were not simple electrical pole shorting noise. So, I connected a whip to my old TS-790S rig and tuned it to 144.390 MHz, the North American APRS frequency.  WALAAAAA, the signals on my monitor connected to a K-3 tuned to 144.150 MHz corresponded perfectly to the WPRS signals on 144.390 MHz, some 240 kHz away! The preamp on the K-3 was off. There were no other receiving preamps in line at the time. Later, I turned on an external 2 Meter preamp and all that happened was that the APRS signals were larger at 144.150 MHz.
>
> It appears that the front end of my K-3 simply folds up in the presence of strong signals that are WAY off the receiving frequency. I can tell you that connecting the same antenna/transverter to a Kenwood TS 590SG, there were no traces of the APRS signals. And connecting the TS-790S to the K1FO likewise produced no APRS QRM at 144.150. To me, with the presence of a number of strong APRS signals on 144.390 makes this K-3 extremely unusable on 2 Meters. I was running the K-3 noise blanker to handle the rest of the noise here but likewise, I also had noise blankers running on the two Kenwood radios as well.
>
> Any suggestions are welcome.  Dick  W5AK  
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[Jim Brown-10]

On 7/27/2018 6:59 PM, Richard Beerman wrote:
> To me, with the presence of a number of strong APRS signals on 144.390 makes this K-3 extremely unusable on 2 Meters. I was running the K-3 noise blanker to handle the rest of the noise here but likewise, I also had noise blankers running on the two Kenwood radios as well.

I agree with Wayne that a noise blanker is responsible for what you are
seeing. FWIW, what these two blankers are CALLED in their setup menu
(long push of NB) is VERY confusing. Fact is, that they are BOTH working
in an IF, one in the first IF and the other in the second. FAR better to
call them IF1 and IF2. NOW it becomes clear which is post-xtal filter.

How we talk about something makes it either easier or more difficult to
understand. That's why I strongly object to use of the word "balun,"
which is used to describe almost a dozen VERY different THINGS, and
multiple meanings of the word "ground," all of them very different from
each other. Another is the phrase "ground loop." All three uses often
cause people to do really dumb things to solve a problem because the
words don't describe what is really going on!

73, Jim K9YC

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[Curt Nixon]

Or perhaps there is a unique mixing of the LO in the Transverter with
similar in the K3 to give a result?    I have never had anything good
result from running the noise blanker in any radio while involved with
2M MS and EME here.  Also usng the K1FO 12 and have APRS as well as
Digital Paging system running a KW about 1 mile away at 144.9   Intermod
can be a crazy thing--especially with mega-FM stations locally.

FWIW

Curt KU8L

On 7/27/2018 10:48 PM, Wayne Burdick wrote:

> Another thought: The K3 has two noise blankers. The hardware blanker does see a broad input frequency range (so it can suppress very fast-rise-time noise pulses), and as with similar blankers, you have to keep the NB threshold high enough to not cause intermod.
>
> Try using just the DSP blanker, which is post-crystal-filter. Or a touch of each. This can be very effective on disparate noise sources.
>
> Wayne
>
>
>
>> On Jul 27, 2018, at 6:59 PM, Richard Beerman <[hidden email]> wrote:
>>
>> Wonder if anyone else has encountered this on 2 Meters? I am using a 12 ele K1FO yagi - about q12 dB gain on 2. That enters the shack where it is connected to a Downeast Microwave 50 Watt transverter with about 17 dB gain on receive. The output of the transverter is connected to transverter input on my old K-3. For the longest time, I was receiving loud QRM from what I initially thought were power line noise bursts. But, I became suspicious because these bursts were about a second or so in duration consistently. During this time, I was testing my setup for meteor scatter using the MSK 144 software found in the current WSJT-X suite. These loud bursts created huge red images on the monitor watching in 144.150 MHz, the MSK144 calling frequency.
>>
>> I got suspicious that these signals were not simple electrical pole shorting noise. So, I connected a whip to my old TS-790S rig and tuned it to 144.390 MHz, the North American APRS frequency.  WALAAAAA, the signals on my monitor connected to a K-3 tuned to 144.150 MHz corresponded perfectly to the WPRS signals on 144.390 MHz, some 240 kHz away! The preamp on the K-3 was off. There were no other receiving preamps in line at the time. Later, I turned on an external 2 Meter preamp and all that happened was that the APRS signals were larger at 144.150 MHz.
>>
>> It appears that the front end of my K-3 simply folds up in the presence of strong signals that are WAY off the receiving frequency. I can tell you that connecting the same antenna/transverter to a Kenwood TS 590SG, there were no traces of the APRS signals. And connecting the TS-790S to the K1FO likewise produced no APRS QRM at 144.150. To me, with the presence of a number of strong APRS signals on 144.390 makes this K-3 extremely unusable on 2 Meters. I was running the K-3 noise blanker to handle the rest of the noise here but likewise, I also had noise blankers running on the two Kenwood radios as well.
>>
>> Any suggestions are welcome.  Dick  W5AK
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[Guy Olinger K2AV]

Although I agree with other points, the DSP noise blanking does not work by
pulse-closing the analog 15 kHz IF. It works in the number soup which is
after the high IF, *and* after the low IF, *and most importantly* after the
analog to digital conversion. DSP NB, being accomplished in the number
soup, is not restricted to the limits of analog methodology. While the
signal being corrected is *representative* of the low IF, it is not
accomplished *in* the IF circuitry and is subject to any outcomes of the
analog to digital conversion.

A good rule for using the IF labeled NB in the K3, is to only use it if it
makes NB on ***that particular noise*** work better, otherwise don't use it
at all. Some of the noise I have around here from time to time is better
blanked with IF + DSP. Other noise is blanked better, sometimes much
better, by DSP only. I'm to the point now where I know what each noise
around here sounds like and can put up the best NB settings right away.
Also some combo's that work well on 160 work poorly on 80m and up.

For the new user of K3 NB, remember that METHODS are also being switched as
you turn the knob, it's not at all like a simple 1 to 10 scale. You can use
a (1st) IF method, and a DSP number soup method, or IF only or DSP only.
When you use both methods, they operate separately in series, with the IF
method necessarily being applied first. It appears, to me at least, that
some DSP methods are diminished by running the IF blanking at the same
time.

For 2 and a half years I had an AC pulse noise on 160 that IF NAR4 + DSP
T1-7 or T2-7 cleared out to below the band noise in a certain 5-6 kHz range
and less efficiently away from that. Contest operation in that range was
equal to no pulse noise. It turned out to be leakage in a splice in the
13kV buried line to easterly neighbors' power transformer. When the splice
hard arced this spring, that noise went away and has never returned. The
fuse blow up on the feed pole across US 64 sounded like a bomb. It rattled
windows. They replaced all the buried 13kV line off that aerial 13 kV feed
to our transformers. Noise has never come back. Currently the IF blanker is
not useful for any noise I run into here. That could change, of course, at
any time  :>))

73, Guy K2AV

On Sat, Jul 28, 2018 at 12:10 AM, Jim Brown <[hidden email]>
wrote:

> . Fact is, that they are BOTH working in an IF, one in the first IF and
> the other in the second. FAR better to call them IF1 and IF2. NOW it
> becomes clear which is post-xtal filter.
>
>
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[wayne burdick]

Thanks, Guy.

A couple of other tips:

1. A small amount of NR (noise reduction) can be used along with the noise blanker to perform a bit of signal clean-up.

2. Most of us run with too much gain and/or too much AGC, in some cases making it sound like the noise blanker is doing less that it really is. I strongly recommend starting with preamp OFF and experimenting with AGC off as well to really hear the effect of the NB.

3. If you’re using CW, crank down the WIDTH control and also try APF. This can remove even more noise with zero signal degradation. (The APF works wonders on weak signals near the noise floor.)

73,
Wayne
N6KR

> On Jul 28, 2018, at 10:17 AM, Guy Olinger K2AV <[hidden email]> wrote:
>
> Although I agree with other points, the DSP noise blanking does not work by
> pulse-closing the analog 15 kHz IF. It works in the number soup which is
> after the high IF, *and* after the low IF, *and most importantly* after the
> analog to digital conversion. DSP NB, being accomplished in the number
> soup, is not restricted to the limits of analog methodology. While the
> signal being corrected is *representative* of the low IF, it is not
> accomplished *in* the IF circuitry and is subject to any outcomes of the
> analog to digital conversion.
>
> A good rule for using the IF labeled NB in the K3, is to only use it if it
> makes NB on ***that particular noise*** work better, otherwise don't use it
> at all. Some of the noise I have around here from time to time is better
> blanked with IF + DSP. Other noise is blanked better, sometimes much
> better, by DSP only. I'm to the point now where I know what each noise
> around here sounds like and can put up the best NB settings right away.
> Also some combo's that work well on 160 work poorly on 80m and up.
>
> For the new user of K3 NB, remember that METHODS are also being switched as
> you turn the knob, it's not at all like a simple 1 to 10 scale. You can use
> a (1st) IF method, and a DSP number soup method, or IF only or DSP only.
> When you use both methods, they operate separately in series, with the IF
> method necessarily being applied first. It appears, to me at least, that
> some DSP methods are diminished by running the IF blanking at the same
> time.
>
> For 2 and a half years I had an AC pulse noise on 160 that IF NAR4 + DSP
> T1-7 or T2-7 cleared out to below the band noise in a certain 5-6 kHz range
> and less efficiently away from that. Contest operation in that range was
> equal to no pulse noise. It turned out to be leakage in a splice in the
> 13kV buried line to easterly neighbors' power transformer. When the splice
> hard arced this spring, that noise went away and has never returned. The
> fuse blow up on the feed pole across US 64 sounded like a bomb. It rattled
> windows. They replaced all the buried 13kV line off that aerial 13 kV feed
> to our transformers. Noise has never come back. Currently the IF blanker is
> not useful for any noise I run into here. That could change, of course, at
> any time  :>))
>
> 73, Guy K2AV
>
> On Sat, Jul 28, 2018 at 12:10 AM, Jim Brown <[hidden email]>
> wrote:
>
>> . Fact is, that they are BOTH working in an IF, one in the first IF and
>> the other in the second. FAR better to call them IF1 and IF2. NOW it
>> becomes clear which is post-xtal filter.
>>
>>
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[Richard Beerman-2]

Thanks to Wayne and others who took time to reply to my inquiry. Because you all cared enough to offer help, I went back over this problem today and have some answers. First of all, Wayne, Jim and Guy were on the money regarding the NB. But first, let me go back a bit. I was listening on 144.150 mHz upper side band; no preamp on with the K-3. No other preamp in line. I am using the K-3 as an IF for a new Downeast Microwave 2 meter transverter. This transverter offers about 17 dB receive gain to the K-3 at 28 mHz, the IF frequency. The transverter is connected to a K1FO yagi with about 12 dB forward gain. The line audio output of the K-3 was patched to the mic input of a Dell PC that was running MSK 144, a program in the WSJT-X suite of software, and I was testing the system to run in upcoming meteor showers. Suddenly, I was interfered with by APRS local signals transmitting at 144.390 mHz.

Everyone was very helpful in making me understand how the two noise blankers in the K-3 work. Your comment, Jim, about calling them NB1 and NB2 is absolutely correct! This is what Kenwood does on their TS-5909SG radio. So, I tuned the TS-790S to 144.39 mHz and being a Saturday, there was plenty of activity. The local APRS station that is closest to my QTH must be really close because he pins the S meter on the 790S connected only to a mobile whip in my steel building. That is the signal that appears at 144.15 mHz on my K-3. APRS is FM and I assume that these signals are generated by a transmitter operating in Class C. Just looking at the signal on my monitor that is printing the activity on 144.15 mHz, it looked pretty dirty. And I am listening on upper side band.

There is a large signal entering the transverter input port on the K-3, given the antenna gain, the receiver gain of the transverter and the large APRS signal. Operating the noise blanker control on the K-3, I discovered that at EVERY setting level using the IF noise blanker, the APRS signal was not just leaking through but was really strong on 144.15 mHz. (Sorry, I was not able to quantify “really loud”, but you get the picture) There was no way to eliminate these APRS signals by changing AGC or eliminating AGC.

Then, I turned off the IF noise blanker and turned on the digital noise blanker. It not only eliminated the APRS QRM at 144.15 mHz, but, it also eliminated much of the power line noise. I ended up at T3-5 setting as best. So I am pretty happy now. I just need to confirm that the digital filter setting does not distort SSB signals by being too aggressive.

Here is my question to the low band crowd on the reflector. You are listening on 160 or 80 meters in the winter. You are having trouble with some kind of noise interference. Your antenna on receive is unity gain or less, but you have a 30 to 40 dB receiving preamp on your receiving antenna. You are running the noise blanker in the IF mode on the K-3. Is it not possible that you are having the same issue as I discovered? The interfering signal is off frequency somewhere relatively close by and the IF noise blanker is somehow opening up the receiver to QRM on the desired receive frequency?

Based upon what I discovered today, there is certainly a issue with the IF noise blanker in the K-3 (don’t know about the other Elecraft radios) where lots of gain is used to amplify weak received signals and where there is (are) very strong (maybe just dirty FM signals) close by. My situation could be easily duplicated.

I now recall that I first noticed this very same problem about 8 years ago with the same K-3 on 2 meters. This was at another QTH with a normal suburban lot and the same antenna. I was receiving a loud interfering signal on 144.2 mHz that I tracked down as cable channel 16 (I think) at about 136 mHz or so. This was also an FM video and audio signal and I am sure that I tried unsuccessfully to eliminate the interference using the K-3’s IF noise blanker. I had the Comcast tech come out and he explained that Comcast disconnected service to a neighbor about 100 feet away. When he said “disconnect” that is what he meant, leaving an exposed center conductor on their coax to radiate. They do not put a short or load on the disconnected line so it just radiates. Nice!

The good news is that the digital noise blanker worked well with my issue. Again, thanks for all the very helpful input!   73’s Dick  W5AK

On Jul 27, 2018, at 8:59 PM, Richard Beerman <[hidden email]> wrote:

>
> Wonder if anyone else has encountered this on 2 Meters? I am using a 12 ele K1FO yagi - about q12 dB gain on 2. That enters the shack where it is connected to a Downeast Microwave 50 Watt transverter with about 17 dB gain on receive. The output of the transverter is connected to transverter input on my old K-3. For the longest time, I was receiving loud QRM from what I initially thought were power line noise bursts. But, I became suspicious because these bursts were about a second or so in duration consistently. During this time, I was testing my setup for meteor scatter using the MSK 144 software found in the current WSJT-X suite. These loud bursts created huge red images on the monitor watching in 144.150 MHz, the MSK144 calling frequency.
>
> I got suspicious that these signals were not simple electrical pole shorting noise. So, I connected a whip to my old TS-790S rig and tuned it to 144.390 MHz, the North American APRS frequency.  WALAAAAA, the signals on my monitor connected to a K-3 tuned to 144.150 MHz corresponded perfectly to the WPRS signals on 144.390 MHz, some 240 kHz away! The preamp on the K-3 was off. There were no other receiving preamps in line at the time. Later, I turned on an external 2 Meter preamp and all that happened was that the APRS signals were larger at 144.150 MHz.
>
> It appears that the front end of my K-3 simply folds up in the presence of strong signals that are WAY off the receiving frequency. I can tell you that connecting the same antenna/transverter to a Kenwood TS 590SG, there were no traces of the APRS signals. And connecting the TS-790S to the K1FO likewise produced no APRS QRM at 144.150. To me, with the presence of a number of strong APRS signals on 144.390 makes this K-3 extremely unusable on 2 Meters. I was running the K-3 noise blanker to handle the rest of the noise here but likewise, I also had noise blankers running on the two Kenwood radios as well.
>
> Any suggestions are welcome.  Dick  W5AK  
> ______________________________________________________________
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[Curt Nixon]

Glad you found a solution Dick:

One thing to note.  Remember that the software decoder in WSJT modes is
looking for very narrow range of signals--most of the time, it will
decode just fine w/o an external noise limiter of any kind. What our ear
hears in noise, the decoder simply ignores.  More damage to the decode
is done by blanking the noise pulses than is fixed.    It just isn't the
same as trying to copy CW or decode PSK.

Curt,  KU8L

On 7/28/2018 9:27 PM, Richard Beerman wrote:

> Thanks to Wayne and others who took time to reply to my inquiry. Because you all cared enough to offer help, I went back over this problem today and have some answers. First of all, Wayne, Jim and Guy were on the money regarding the NB. But first, let me go back a bit. I was listening on 144.150 mHz upper side band; no preamp on with the K-3. No other preamp in line. I am using the K-3 as an IF for a new Downeast Microwave 2 meter transverter. This transverter offers about 17 dB receive gain to the K-3 at 28 mHz, the IF frequency. The transverter is connected to a K1FO yagi with about 12 dB forward gain. The line audio output of the K-3 was patched to the mic input of a Dell PC that was running MSK 144, a program in the WSJT-X suite of software, and I was testing the system to run in upcoming meteor showers. Suddenly, I was interfered with by APRS local signals transmitting at 144.390 mHz.
>
> Everyone was very helpful in making me understand how the two noise blankers in the K-3 work. Your comment, Jim, about calling them NB1 and NB2 is absolutely correct! This is what Kenwood does on their TS-5909SG radio. So, I tuned the TS-790S to 144.39 mHz and being a Saturday, there was plenty of activity. The local APRS station that is closest to my QTH must be really close because he pins the S meter on the 790S connected only to a mobile whip in my steel building. That is the signal that appears at 144.15 mHz on my K-3. APRS is FM and I assume that these signals are generated by a transmitter operating in Class C. Just looking at the signal on my monitor that is printing the activity on 144.15 mHz, it looked pretty dirty. And I am listening on upper side band.
>
> There is a large signal entering the transverter input port on the K-3, given the antenna gain, the receiver gain of the transverter and the large APRS signal. Operating the noise blanker control on the K-3, I discovered that at EVERY setting level using the IF noise blanker, the APRS signal was not just leaking through but was really strong on 144.15 mHz. (Sorry, I was not able to quantify “really loud”, but you get the picture) There was no way to eliminate these APRS signals by changing AGC or eliminating AGC.
>
> Then, I turned off the IF noise blanker and turned on the digital noise blanker. It not only eliminated the APRS QRM at 144.15 mHz, but, it also eliminated much of the power line noise. I ended up at T3-5 setting as best. So I am pretty happy now. I just need to confirm that the digital filter setting does not distort SSB signals by being too aggressive.
>
> Here is my question to the low band crowd on the reflector. You are listening on 160 or 80 meters in the winter. You are having trouble with some kind of noise interference. Your antenna on receive is unity gain or less, but you have a 30 to 40 dB receiving preamp on your receiving antenna. You are running the noise blanker in the IF mode on the K-3. Is it not possible that you are having the same issue as I discovered? The interfering signal is off frequency somewhere relatively close by and the IF noise blanker is somehow opening up the receiver to QRM on the desired receive frequency?
>
> Based upon what I discovered today, there is certainly a issue with the IF noise blanker in the K-3 (don’t know about the other Elecraft radios) where lots of gain is used to amplify weak received signals and where there is (are) very strong (maybe just dirty FM signals) close by. My situation could be easily duplicated.
>
> I now recall that I first noticed this very same problem about 8 years ago with the same K-3 on 2 meters. This was at another QTH with a normal suburban lot and the same antenna. I was receiving a loud interfering signal on 144.2 mHz that I tracked down as cable channel 16 (I think) at about 136 mHz or so. This was also an FM video and audio signal and I am sure that I tried unsuccessfully to eliminate the interference using the K-3’s IF noise blanker. I had the Comcast tech come out and he explained that Comcast disconnected service to a neighbor about 100 feet away. When he said “disconnect” that is what he meant, leaving an exposed center conductor on their coax to radiate. They do not put a short or load on the disconnected line so it just radiates. Nice!
>
> The good news is that the digital noise blanker worked well with my issue. Again, thanks for all the very helpful input!   73’s Dick  W5AK
>
> On Jul 27, 2018, at 8:59 PM, Richard Beerman <[hidden email]> wrote:
>> Wonder if anyone else has encountered this on 2 Meters? I am using a 12 ele K1FO yagi - about q12 dB gain on 2. That enters the shack where it is connected to a Downeast Microwave 50 Watt transverter with about 17 dB gain on receive. The output of the transverter is connected to transverter input on my old K-3. For the longest time, I was receiving loud QRM from what I initially thought were power line noise bursts. But, I became suspicious because these bursts were about a second or so in duration consistently. During this time, I was testing my setup for meteor scatter using the MSK 144 software found in the current WSJT-X suite. These loud bursts created huge red images on the monitor watching in 144.150 MHz, the MSK144 calling frequency.
>>
>> I got suspicious that these signals were not simple electrical pole shorting noise. So, I connected a whip to my old TS-790S rig and tuned it to 144.390 MHz, the North American APRS frequency.  WALAAAAA, the signals on my monitor connected to a K-3 tuned to 144.150 MHz corresponded perfectly to the WPRS signals on 144.390 MHz, some 240 kHz away! The preamp on the K-3 was off. There were no other receiving preamps in line at the time. Later, I turned on an external 2 Meter preamp and all that happened was that the APRS signals were larger at 144.150 MHz.
>>
>> It appears that the front end of my K-3 simply folds up in the presence of strong signals that are WAY off the receiving frequency. I can tell you that connecting the same antenna/transverter to a Kenwood TS 590SG, there were no traces of the APRS signals. And connecting the TS-790S to the K1FO likewise produced no APRS QRM at 144.150. To me, with the presence of a number of strong APRS signals on 144.390 makes this K-3 extremely unusable on 2 Meters. I was running the K-3 noise blanker to handle the rest of the noise here but likewise, I also had noise blankers running on the two Kenwood radios as well.
>>
>> Any suggestions are welcome.  Dick  W5AK
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