Re: Terrestrial QRM to FM satellites
Today on passes of both SO-50 and AO-27, there were terrestrial QSOs going on. It was especially bad on AO-27...
Three comments:
1) When you are not doing satellite passes, shift your two meter rig to 145.85 and LISTEN all day. 90% of the US population lives in cities (or something like that) and so the chances are that some one will hear them direct.
2) Its in the cities that the repeater density is so high that some new hams might feel there is no other place to put up a local non-coordinated repeater. So we probably have a good chance of somneone on this BB hearing them.
3) Listen for 9600 baud Packet noise bursts. At least they are identifiable. One of the packet uplinks on GO-32 shares the same 2m uplink as AO-27. This is why we have to prohibit unattended packet operation via GO-32 on its 145.85 uplink.
I will modify my GO-32 APRS user operations web page to make sure this point is clear.
Bob, Wb4APR
On Sep 20, 2007, at 9:29 PM, Bob Bruninga wrote:
- Its in the cities that the repeater density is so high that some
new hams might feel there is no other place to put up a local non- coordinated repeater. So we probably have a good chance of somneone on this BB hearing them.
I missed if the QRM is known to be voice or if Bob's note here makes it sound more like it's a packet station, but if voice...
These transmissions could be coming from some of the "other things" -- new technologies that sound like repeaters, but aren't... that are popular lately on 2m FM simplex.
Auxiliary Station operation in 2m is now legal, and many newer hams setting up things like EchoLink and IRLP simplex stations really aren't very careful sometimes about where they park them in the band. In most cases, it's NOT malicious, but it can sure be frustrating to find them and explain to them about the unintentional interference they might be causing.
I was on the "stop doing that kids, it's illegal" bandwagon up until the rule change, now I'm still on the "please, put your favorite toy on 222, UHF or higher, kids! VHF is kinda "full" in most big cities, even if you stick to the bandplan" bandwagon.
The manufacturers really make this above-mentioned situation so much worse by selling VHF-only radios as "cost" or "loss leader" products to entice new hams into buying them. They really need a better marketing plan that doesn't stuff VHF so full to the gills that interference can't be helped. Please support and applaud any manufacturer who's UHF single band radios (if they even have any) are as inexpensive to purchase as their VHF's. Right now, I don't think a single manufacturer of ham rigs meets that, or has even given a thought to what they're doing to VHF.
As a major volunteer for IRLP, I would remind folks that if it turns out to be something like IRLP, EchoLink etc... please don't taint your viewpoint of these technologies, or get overly-emotional about the "source" being one of those networks... the networks are just linking technologies, but many hams really don't know when and where it's appropriate to link things into simplex FM -- especially on 2m FM simplex.
To them, they don't even always know that there even ARE such things as satellite uplinks in the VHF band. Seriously. Strange thought to the AMSAT crowd, but we've run across complaints (non-satellite) before of IRLP simplex nodes interfering with long-standing users of VHF simplex frequencies.
Also keep in mind that if someone does copy something and reports it here to the list, the voices/callsigns they hear might not even be the callsigns of the operator of the "incorrectly placed" link/ Auxiliary Station.
You may have to tread lightly if you find out who it is, and ask them if they were operating via a Reflector or Conference Server during the timeframe of the interference, and even then, they may not know for sure.
The only thing you might know for sure if you listen to 145.85 locally and hear something that's not a satellite transmission, is that the transmitter actually causing the interference is in your area... from that point, some knowledgeable and experienced sleuths may be required to help figure out what exactly it is... and of course, a good DF'ing crew doesn't hurt either!
Just thoughts. I hope that this isn't what it turns out to be...
-- Nate Duehr, WY0X nate@natetech.com
At 04:36 PM 9/21/2007, Nate Duehr wrote:
I was on the "stop doing that kids, it's illegal" bandwagon up until the rule change, now I'm still on the "please, put your favorite toy on 222, UHF or higher, kids! VHF is kinda "full" in most big cities, even if you stick to the bandplan" bandwagon.
That's the case here too now. I'm glad I decided to do something different and make my 2m output SSB, as that and D-STAR are really the only options available here, without reading on someone's toes. And as much as I'd like to run a D-STAR gateway, my budget will only cover one D-STAR capable radio, not two.
The manufacturers really make this above-mentioned situation so much worse by selling VHF-only radios as "cost" or "loss leader" products to entice new hams into buying them. They really need a better marketing plan that doesn't stuff VHF so full to the gills that interference can't be helped. Please support and applaud any manufacturer who's UHF single band radios (if they even have any) are as inexpensive to purchase as their VHF's. Right now, I don't think a single manufacturer of ham rigs meets that, or has even given a thought to what they're doing to VHF.
Dunno if it's the same in the States, but 2m has such a long history of club nets and other groups that users have spread right through the band. It's literally very difficult to find a frequency that doesn't have some sort of use. Fortunately, everyone steers clear of the satellite allocation. The only free space now is in the SSB segment and now on D-STAR, which can fit in between our FM channels.
As a major volunteer for IRLP, I would remind folks that if it turns out to be something like IRLP, EchoLink etc... please don't taint your viewpoint of these technologies, or get overly-emotional about the "source" being one of those networks... the networks are just linking technologies, but many hams really don't know when and where it's appropriate to link things into simplex FM -- especially on 2m FM simplex.
The best approach is to play Elmer, calmly explaining what's happening and offering advice, and perhaps inviting them to work satellites. I once modified my IRLP node to act as a crossband repeater with an output in the satellite band, so I could have more power on the uplink of UO-14, to help overcome the severe Asian QRM on its input. I used another band besides 70cm, so I didn't desense my downlink. :-)
Also keep in mind that if someone does copy something and reports it here to the list, the voices/callsigns they hear might not even be the callsigns of the operator of the "incorrectly placed" link/ Auxiliary Station.
It's not a bad idea to make contact with those people though, they may know the node owner and may pass on your concerns. Sometimes that can reap rewards. In any case, they may know someone that uses the offending link, who can pass on the message. Networking sometimes bears fruit.
The only thing you might know for sure if you listen to 145.85 locally and hear something that's not a satellite transmission, is that the transmitter actually causing the interference is in your area... from that point, some knowledgeable and experienced sleuths may be required to help figure out what exactly it is... and of course, a good DF'ing crew doesn't hurt either!
Dfing certainly helps, that usually yields a location that can be used for a callsign lookup and hopefully an email address to make contact, assuming the owner isn't able to come up on the air (do that between passes! :D ).
73 de VK3JED http://vkradio.com
...if you listen to 145.85 and hear something... ... from that point, some knowledgeable and experienced sleuths may be required to help...
Stump on.
And that is where we need to educate all VHF'ers, and that is that we don't need DF equip, we don't need beams, and we don't need experts. Anyone with a mobile radio and/or an HT with stock omni antenna, and a little spare time for some fun driving, can find a transmtter ... the closer you get to a transmitter the stronger it is.
See http://www.ew.usna.edu/~bruninga/dfing.html Scan quickly down the page about 2/3rds to the most recent Balloon recovery and you can see how easy it is..
The web page says "APRS Dfing" but ignore the APRS part. You don't need APRS and you don't need a PC. Just drive while watching the AVERAGE VALUE of the S meter... And visualizing what's going on. There are two easy techniques for "DFing" using signal strength alone.
INDIVIDUAL: Average Signal Strength is a very significant indicator that can be used to home in on a signal. Combined with local terrain knowledge, a little driving and chris-crossing can quickly give knowledge of the signal profile and allow the driver to just keep narrowing down on the signal and with enough time, arrive at the door.
Just remember the Smeter average value where you first start hearing the signal and then drive straight watching this indication improve and then fade back to this level. These two points are more or less equidistant from the source. Now drive back to the middle where now you know it was strongest, and make a 90 degree turn. See the new Smeter average. Again, drive straight through the peak to the same reading on the other side. Again, go back to the center of that leg. See the new Smeter average. Turn another 90 degrees. Repeat. Eventually you arrive at the door of the signal.
GROUP: Spot signal strength reported by a large number of ham mobiles or fixed stations can instantaneously narrow down the search to a neighborhood. The BIGGEST mistake made here is the fact that most people collecting reports tend to -ignore- the null reports of nothing-heard. When in fact, that is often where the most useful initial data is! There are usually far more reports of nothing-heard than heard. And it is that large amount of data that shows where the signal -ISN'T- that is the biggest contributor to knowing where not to search! Focus then on more reports from other areas not reporting -nothing-heard. This should only take a call up on the local voice repeater asking for people to listen for the signal and make spot reports.
Once an area is found with reports of -HEARD- then go drive, and use the individual technique of signal strength and drive right to the door. Its fun, anyone can do it... If you have enough gas.
These techniques are built into APRS, but that is only for easy visuilization of location on the map as the solution develops. (And everyone watching can see it in real time...) But this hardware and APRS and maps are absolutely not needed. Just drive and watch the Smeter.
When you get to MAX signal and the mobile Smeter is max'ed, then you need your HT sitting on the seat with its ruber duck becomes the benchmark. Once it is full quieting, you can usually remove its antenna and stick in shorter and shorter paper clip as you get closer and closer. Eventually the HT will hear the signal with no antenna. Now it is time to get out of the car and walk. Holding the HT on your chest. You have a NULL out your back. Use it to get walking directions and by now you are within yards of the source.
Bob, WB4APR
At 11:16 PM 9/21/2007, Robert Bruninga wrote:
INDIVIDUAL: Average Signal Strength is a very significant indicator that can be used to home in on a signal. Combined with local terrain knowledge, a little driving and chris-crossing can quickly give knowledge of the signal profile and allow the driver to just keep narrowing down on the signal and with enough time, arrive at the door.
While I can do this quite well (and we used to have CB foxhunts that worked on this very principle), there are some inexpensive add ons that can make DFing that much easier, such as an attenuator box, which has variable attenuation, selectable by switches on the front panel. The attenuator will allow you to get in closer without saturating your S meter. Quite cheap to put together out of a metal box and a bunch of metal film resisters. The other is a small Yagi. The VK3VT 3 element design has been proven over 30 years and works well, with a good pattern.
The biggest danger of hunting with an omni is chasing reflections, especially in built up or hilly areas. Even with a directional antenna, this sometimes confuses the experts. :)
When you get to MAX signal and the mobile Smeter is max'ed, then you need your HT sitting on the seat with its ruber duck becomes the benchmark. Once it is full quieting, you can usually remove its antenna and stick in shorter and shorter paper clip as you get closer and closer. Eventually the HT will hear the signal with no antenna. Now it is time to get out of the car and walk. Holding the HT on your chest. You have a NULL out your back. Use it to get walking directions and by now you are within yards of the source.
Strangely enough, this has never really worked for me, much to my surprise. Dunno why.
73 de VK3JED http://vkradio.com
... Now it is time to get out of the car and walk. Holding HT on your chest. You have a NULL out your back. Use it to get walking directions and by now you are within yards of the source.
... this has never really worked for me, much to my surprise. Dunno why.
It is subtle. In fact, a lot of this signal strength tracking is really by ear. Just listening to aggregate of the degree of quieting and the rise and fall of the background FM noise. The S meter just gives a benchmark now and then.
When walking with the HT, I periodically stop and with the HT held tightly to chest, do a perroiette (I have no clue how to spell a french dancing maneuver)... Lets call it a spin in place. My ear hears the subtle peaks in the back ground noise. The direction of my back on those subtle and narrow noise level peaks is generally the direction to go next.
Or something like that. Doing this in a field of 8 foot tall corn with razor sharp leaves and a sunburn tends to make one not want to go in the wrong direction for too long. (Finding a downed balloon)...
Bob, WB4APR
On Fri, 21 Sep 2007 18:10:05 -0400, Robert Bruninga wrote:
... Now it is time to get out of the car and walk. Holding HT on your chest. You have a NULL out your back. Use it to get walking directions and by now you are within yards of the source.
... this has never really worked for me, much to my surprise. Dunno why.
When walking with the HT, I periodically stop and with the HT held tightly to chest, do a perroiette (I have no clue how to spell a french dancing maneuver)... Lets call it a spin in place. My ear hears the subtle peaks in the back ground noise. The direction of my back on those subtle and narrow noise level peaks is generally the direction to go next.
There's also another way. A garden-variety rubber duck will often have a fairly sharp null off the end of the antenna. Hold the HT horizontally in the clear away from your body and spin it around. Where the signal shows the sharpest null, your antenna will be pointing at the source. You can check for this behavior with a known signal source before you try DFing.
-- Ham Radio NU0C TR7/RV7, TR6/RV6, T4XC/R4C, L4B, NCL2000, SB104A, R390A, GT550A/RV550A, HyGain 3750, IBM PS/2 - all vintage, all the time!
HyGain 3750 User's Group - http://groups.yahoo.com/group/HyGain_3750/
At 08:10 AM 9/22/2007, Robert Bruninga wrote:
It is subtle. In fact, a lot of this signal strength tracking is really by ear. Just listening to aggregate of the degree of quieting and the rise and fall of the background FM noise. The S meter just gives a benchmark now and then.
I actually did test it in situations where I knew the source, and got the wrong result.
When walking with the HT, I periodically stop and with the HT held tightly to chest, do a perroiette (I have no clue how to spell a french dancing maneuver)... Lets call it a spin in place. My ear hears the subtle peaks in the back ground noise. The direction of my back on those subtle and narrow noise level peaks is generally the direction to go next.
I see, might give it another try. :)
Or something like that. Doing this in a field of 8 foot tall corn with razor sharp leaves and a sunburn tends to make one not want to go in the wrong direction for too long. (Finding a downed balloon)...
Hehe, I usually have a sniffer on hand. Being an ARDFer helps. ;)
73 de VK3JED http://vkradio.com
I had no idea how much sleuthing could be done with this short file. Those who are attempting decoding of the AFSK signal might prefer to work with an uncompressed version, which was originally recorded with 'audacity', the open-source, cross-platform audio editor. The audacity files are available as a tar.gz file at http://localhost/Amsat/ .
73, Bruce VE9QRP
Quoting Bruce Robertson broberts@mta.ca:
I had no idea how much sleuthing could be done with this short file. Those who are attempting decoding of the AFSK signal might prefer to work with an uncompressed version, which was originally recorded with 'audacity', the open-source, cross-platform audio editor. The audacity files are available as a tar.gz file at http://localhost/Amsat/ .
Well, it's 'localhost' here, anyway :-)
Make that http://heml.mta.ca/Amsat/
Sorry
73, Bruce VE9QRP
Bruce,
Thanks for sharing....is that a trunking system?
The sad thing is, this QRM is hitting AO-27 better than my intentional signals sometimes! ;-)
73,
Dave N0TGD
On 9/21/07, Bruce Robertson broberts@mta.ca wrote:
Quoting Bruce Robertson broberts@mta.ca:
I had no idea how much sleuthing could be done with this short file. Those who are attempting decoding of the AFSK signal might prefer to work with an uncompressed version, which was originally recorded with 'audacity', the open-source, cross-platform audio editor. The audacity files are available as a tar.gz file at http://localhost/Amsat/ .
Well, it's 'localhost' here, anyway :-)
Make that http://heml.mta.ca/Amsat/
Sorry
73, Bruce VE9QRP _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
I took a listen to the audio file and what you're hearing is an MDC1200 status indicator from a Motorola radio. You typically hear these on police frequencies but since they're easily modifiable to the ham bands you'll hear them with the encoder still enabled on ham radio, too. I took the audio file and decoded it with WinMDCD (freeware) and it reveals nothing too interesting:
TIME OP ARG ID DESCRIPTION ----------------------------------------------------- 00:00:05.5 01 00 0424 POST UNIT ID 00:00:06.4 01 00 0424 POST UNIT ID 00:00:09.7 01 00 A900 POST UNIT ID 00:00:24.0 01 00 A900 POST UNIT ID 00:00:46.4 01 00 A900 POST UNIT ID
00:00:11.3 NO DECODE 00:00:20.8 NO DECODE
I edited the time stamps to reflect the time shown in the audacity sound file.
73, Mark
I've been monitoring 145.850 here in the western suburbs of Chicago with VoxRecorder for the past couple of days, and not heard anything. Either the QRM'ing stations haven't been on, or they are not in this area.
73, George, KA3HSW
I have monitored 145.850 all week here in the Chicago suburbs, and not heard a thing.
I took Bruce's recording of the QRM and boosted the audio in Audacity, then slowed it down, and I'm pretty sure I can hear a snippet of a VE call in there, and a hint of a north-of-the-border accent on one of the stations.
George, KA3HSW
participants (9)
-
Bob Bruninga -
Bruce Robertson -
Dave hartzell -
George Henry -
Jim Shorney -
Mark Saurman -
Nate Duehr -
Robert Bruninga
-
Tony Langdon