[NLRS] 2m Pager? noise

Sun Oct 29 14:54:32 EDT 2017

On 10/28/2017 7:21 PM, Kirk P wrote:
>
>
> I sure appreciate all the information and ideas. Yes, Im sure its
> APRS as thats its freq.
>
>
> Not sure there is anything now that I can do as they are operating
> within their rights though some seem awfully over modualted.
>
>
> It would appear that my only hope would be to find some type of
> filter I can set for a freq up higher in band that can just catch
> .380 on its lower edge..a cavity that I can adjust perhaps? I dont
> know..so much of this VHF stuff is newer to and above my
> knowledge..HF Id have it solved already HI HI
>
That filter will be difficult and not perform well attenuating the APRS 
signal without killing the EME signal from filter loss.

You could try a coaxial notch filter. Start with a coax T in the receive 
line and on the side of the T connect 1/8th wave of good coax and 
terminate the open end with a variable capacitor having reactance equal 
to the characteristic impedance of the coax. E.G. 50 ohms reactance at 
144.390 and about 8 inches of RG8 or RG213 or LMR 400. The capacitor 
would be about 23 pf at resonance. Tune the capacitor to minimize the 
APRS signal. Enclose the capacitor in a shield because its a high 
impedance and any exposed conductor will be a receive antenna countering 
the desired notch. I sued such a scheme once to take down a FM broadcast 
signal from a mile away that was upsetting my rig. It worked. The notch 
may not be narrow enough for your situation.
>
> I modified my 746PRO to accept a SDR RX as its RX...I use both the
> Funcube PRO+ as well as RTL dongles for 160m-2m utilizing the 746 as
> the TX radio. Amazed at how well the RX is now that Ive done
> this..but it appears to come at a price..the dongles have a bandwidth
> of up to 1mhz of RX and the FC at 196khz and fold under such strong
> local signals when coupled with WSJTX for EME.

The RF bandwidth of the dongle may be more like at GHz so it has to 
digitize the super strong signal and runs out of digitial bits for the 
super weak EME signal.

Since you have modified the 746, I'd consider (though I'm not a fan of 
Icom radios due to bad experiences long ago with an IC-211) modifying 
the 746 to put out an IF signal after the roofing filter of the first IF 
for the dongle SDR. That filter is probably 15 or 20 kHz wide and would 
protect the dongle very well. Then I would add attenuation after then 
preamp but no more than will allow the full gain system NF or MDS to be 
the same. Could measure by sun noise or moon noise also. Point in my 
paper I referenced is that for maximum dynamic range the front end gain 
needs to only be the minimum that gets the best system NF or MDS. More 
gain than that just hurts strong signal handling.
http://geraldj.networkiowa.com/papers/EME/Intermod2.pdf

The FM FSK bandwidth probably isn't over modulated for FM, just the FM 
bandwidth is more like 15 kHz double side band where AM for the same 
audio would be under 5 kHz double side band. And SSB would be under 2.5 kHz.
>
> If I use just th746PRO as the RX in its original configuration (Yes,
> I can switch back and forth the way I did the mod) it handles this
> noise up the band much better..though doesnt hear weak signal as well
> as the SDR using SDR console software.
>
>
> Anyone that give me filtering ideas Im open to suggestions.
>
>
> PAR electronics got back to me and said no way.
>
>
> They did mention a HIGH IP3 LNA as an option though Im not familiar
> with those. I currently use the ARR 144 LNA.

A high IP3 LNA means it can handle stronger signals without intermod of 
those signals.

When APRS first came along I suggested to the world that their frequency 
should be 145.790, just outside the satellite band and the world agreed. 
That kept it away from weak signal and EME and from repeater inputs. 
Unfortunately hams on the space station didn't understand FM bandwidth 
and insisted on using 146.800 the band edge for satellite signals and 
complained about QRM from APRS down 10 kHz. Had they understood that 
half their bandwidth was outside the satellite band and moved up 10 or 
20 kHz there would not have been a problem. But they wouldn't move so 
APRS moved to 144.390 and you are experiencing the bad results of that move.

73, Jerry, K0CQ
>
>
> Kirk, N0KK
>
>
> Sent from Outlook<http://aka.ms/weboutlook>
>
>
> ________________________________ From:
> nlrs-bounces at mailman.qth.net<nlrs-bounces at mailman.qth.net>  on behalf
> of Mary Brown<maryalanab at gmail.com> Sent: Saturday, October 28, 2017
> 2:38 PM To: geraldj at netins.net; nlrs at mailman.qth.net Subject: Re:
> [NLRS] 2m Pager? noise
>
>
>
> You have KE0CRW-10 RX I-Gate in New Hope, KD0TLS-7 also on APRS,
> either could be the source...
> https://aprs.fi/#!addr=New%20Hope%2C%20MN
>
> Mary W0AAT
>
> -----Original Message----- From: nlrs-bounces at mailman.qth.net
> [mailto:nlrs-bounces at mailman.qth.net] On Behalf Of Dr. Gerald N.
> Johnson Sent: Saturday, October 28, 2017 1:52 PM To:
> nlrs at mailman.qth.net Subject: Re: [NLRS] 2m Pager? noise
>
>
>
> 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
>>
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