Interference with STL on 900mhz.

[johnny05]

I'm having a problem with our Country station..... Every now and then, I get the "stutter" effect.. It happened again tonight and completly ruined my night.... Signal strength 100%, quality takes a nosedive... What could be interfering?

 

[tpt]

1. Some kind of spread-spectrum device.

2. Cell phone equipment. I've heard audio from an analog cell get into an STL at one time. More likely PLL circuit temporarily going nuts. Unfortunately, you may need a spectrum analyser and a directional antenna (remember those small yagis for 800 mhz?) to find out where it is coming from.

3. A sweeper. Saw this when tracking interference on a satellite downlink. (satellite is, of course, higher, but we thought it might be getting into the LNBa mixing with the 1.2 g feed out of it). Started out around 900 and swept up to around 1300 (which was the top end of this particular analyser. Have no idea what it was, didn't come from our nearby cell site.

 

[taylorengineer]

> 1. Some kind of spread-spectrum device.
>
> 2. Cell phone equipment. I've heard audio from an analog
> cell get into an STL at one time. More likely PLL circuit
> temporarily going nuts. Unfortunately, you may need a
> spectrum analyser and a directional antenna (remember those
> small yagis for 800 mhz?) to find out where it is coming
> from.
>
> 3. A sweeper. Saw this when tracking interference on a
> satellite downlink. (satellite is, of course, higher, but we
> thought it might be getting into the LNBa mixing with the
> 1.2 g feed out of it). Started out around 900 and swept up
> to around 1300 (which was the top end of this particular
> analyser. Have no idea what it was, didn't come from our
> nearby cell site.
>
while you have the spectrum analyser out, check the transmitter. If this is a digital, non compressed, STL, like a CD-Link or Moseley 9003, than the transmitter can go non linear and cause this type problem. It happened to me once with a CD-Link. Look at spectrum output for spurs.
I also had interference issues, as explained above by tpt.A cavitiy filter(s) will probably cure this problem.

 

[Andy_Brown]

> I'm having a problem with our Country station..... Every now
> and then, I get the "stutter" effect.. It happened again
> tonight and completly ruined my night.... Signal strength
> 100%, quality takes a nosedive... What could be interfering?
>

Check with the frequency co-ordinator in your region for any new
services established recently that may cut across your path or studio or
xmtr site. If your xmtr/STL receiver is at a site that is a farm, ask around
and see if anyone has just replaced any equipment or antenna --- I have had two way repeaters in the high 400's throw stuff out close enough to 950 to cause intermittent jazz in the STL receiver ... probably coming in through the STL dish although it was less than 50 yards away and might have been going right in the building we were in. Turned out they forgot to tighten some screws in their transmission line/filters causing them to not only have VSWR problems but creating an intermittent flutter in our STL's (main or backup) which really had me going for a while. I was banished to the transmitter site to fix the problem ... on about my 3rd trip for this problem I ran into the engineer for the repeater and got the scoop. Had I not, it would have disappeared anyway since they were aware of their own VSWR problem, but not the interference.<P ID="signature">______________
Electricity is really just organized lightning.
~George Carlin</P>

 

[BrokeEngineer]

we can help but...

Give some more info....what type of STL, antenna, how far is the shot, what's in the path (trees, buildings, whatever). What are the settings on the STL Xmtr and Rec.(we had to change our settings do to problems). Are you the only station on the tower? Just provide some details as this problem could be as deep as "I have a ground hum in insert place here".