[NLRS] 2m Pager? noise

[Dr. Gerald N. Johnson]

While intermod of out of band signals isn't impossible, its almost 
certain the signal at 144.390 is APRS, 1200 baud packet. 
http://www.twinslan.net/packet.html says listen on 145.01, 145.67 and 
144.390 to hear packet signals. At least a couple should be 1200 baud 
AFSK, 145.67 might be 9600 baud FSK which sounds like noise. Around here 
144.390 is still 1200 baud packet according to my ears. Other than APRS 
I think there is very little VHF packet in Iowa now. And the APRS 
graphic locator page shows several APRS stations close to N0KK.

73, Jerry, K0CQ

On 10/28/2017 11:40 AM, Chris Elmquist wrote:
>
>
> On Saturday (10/28/2017 at 10:56AM -0500), Dr. Gerald N. Johnson wrote:
>
> [... snip ...]
>
>> I have it on line at:
>> http://geraldj.networkiowa.com/papers/EME/Intermod2.pdf
>> Intermod from other band activity is not a new EME problem.
>
> If you determine it is actually intermod, I have had good success with
> a notch filter from PAR Electronics,
>
> http://www.parelectronics.com/amateur.php
>
> His approach is to notch one or more of the out of band signals enough that
> intermod is no longer an issue in your front end.
>
> I was playing with one of the super cheepy Chinese 2m FM rigs (a
> TYT-9000D) and found that two signals in the 152 to 157 range were
> mixing and ending up on 146.4'ish, plain as day.  I wasn't sure why
> W0GHZ was dispatching ambulances on our "intercom" frequency  ;-)
>
> After I determined the exact frequency of the real ambulance service,
> PAR built the filter to notch it out and the problem was solved.
>
> Now, these won't take 1500W EME transmit power so you would have to put
> this in your receive-only path somehow if you are transmitting with more
> than about 50W I think.
>
> PAR (aka W4OP) do a nice job and give you an insertion-loss&  SWR plot
> for the filter they build, showing in-band and out-of-band losses.
> Well done, IMO.
>
> Chris NØJCF
>
>> On 10/28/2017 7:31 AM, Kirk P wrote:
>>>
>>>
>>> Good morning,
>>>
>>> I recently installed a 4x7 array for EME and a SDR RX for all bands.
>>>
>>>
>>> I have some very loud noise that sounds like a pager system at 144.390.
>>>
>>>
>>> I have tried all measures I can think of to determine if it is my network or something from within my home. I have disabled network, unplugged wifi and router, inserted a 2m bandpass filter etc. No luck.
>>>
>>>
>>> If I move antennas there is no change in signal ...
>>>
>>>
>>> Stumped here looking for ideas. Can anyone else hear this locally or has anyone experienced this at all?
>>>
>>>
>>> My main concern here is that it does at time seem to desense WSJTX ability to hear and decode which of course isn't good if I want to succeed at EME.
>>>
>>>
>>> Kirk N0KK
>>>
>>>
>>> Thank you
>