eHam Forums => RFI / EMI => Topic started by: W3HKK on July 15, 2011, 10:15:46 AM

Title: S9 QRM on 6M
Post by: W3HKK on July 15, 2011, 10:15:46 AM
The club set up at a new QTH -  a hilltop renovated barn with a great view - for the ARRL VHF Test in June.  I checked the area with my auto AM radio and found it very quiet. 

Once we got the yagi up and connected the 6m rig, things were different.  Pointing the yagi North  showed the loudest QRM at S-9.  Rotating it south,  west or east reduced it to S4-5, and enabled us to make 130 QSOs.  But at least another 50 were possible if we could have copied the S-5 sigs calling us. The QRM level was pretty much constant throughout the entire contest.

The rural road and overhead power lines  pass  at their closest point, due North of us, so I assumed that to be the source.
The curious thing is  zero QRM on broadcast and 160M.  Just nice quiet white noise. 

Any thoughts?  We hope to return there in the Fall/winter for the 160M test, and then next summer for the June VHF Test, so resolving the QRM would be a big help.

Title: RE: S9 QRM on 6M
Post by: K1CJS on July 17, 2011, 07:03:12 AM
Have your members got any experience at fox hunting?  If so, get them together and have a fox hunt (the noise) on your six meter radios!

Title: RE: S9 QRM on 6M
Post by: AA4PB on July 17, 2011, 02:12:26 PM
A lot of impulse noise peaks somewhere around 40-50MHz. Collins used to make a noise blanker that contained a 40+MHz receiver to detect the noise and blank the main receiver.

Title: RE: S9 QRM on 6M
Post by: KJ4FUU on July 18, 2011, 12:43:51 PM
Either our cable box, or the Insignia (Best Buy house brand) HDTV causes this very problem. If I ever have a ham move in within a block of me, I will probably be forced to deal with this issue. For the time being, if I want to work 6 meters, I can't watch TV (not that there's anything worth watching anyway).

-- Tom

P.S. Odds are, it's the TV. The box didn't seem to cause a problem when it was hooked to an old analog TV.

Title: RE: S9 QRM on 6M
Post by: K6AER on July 20, 2011, 09:21:37 AM
Take a newer VHF handheld and put it on the VHF aircraft band. Open the squelch. The radio will respond to amplitude noise, Drive down the road with the suspected power line noise. The radio will erupt when you are near the offending pole.

Paint a white X on the pole and call the power company and give them the location of the pole. Most poles have a pole number and record that number for the power company.

Title: RE: S9 QRM on 6M
Post by: W3FJ on July 26, 2011, 04:51:31 PM
If there there is any LED lighting used in the building or near-by, this may cause the problem you're having.
73, Mick

Title: RE: S9 QRM on 6M
Post by: WB2WIK on July 26, 2011, 06:45:28 PM
I just read this and two thoughts come to mind:

1.  It's very weird to have a lot of noise on 6m when it's not there on lower bands.  Power  line noise is almost always worst on the lowest frequency bands and gets better as you go up the spectrum.

2.  If you have a lot of noise in one direction on 6m, I'm guessing you're aiming at a TV CH-2 transmitter.  They operate just above the 6m band and run lots of power, and of course raise noise levels on six meters.

Title: RE: S9 QRM on 6M
Post by: W3HKK on July 29, 2011, 11:55:25 AM
 I found  QRM peaking at S-9 last night on my 6M home station xcvr.

Went around the house shutting off switches on the various lights, inside and out, with no success.  Then I got to the laundry room which has fluorescent lighting.  The XYL was  out there working on a project.  I shut the light off (with her permission!)   and the QRM disappeared. 

The laundry room is about  35 ft  SE of my 6M yagi.  The QRM peaked in a W or SE direction.  Bingo.

So there is one 6M QRM source  identified.