[Elecraft] Horrible APRS QRM on 2 Meters

[Curt]

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 <rbeersr at att.net> 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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