V
VideoPaul
Guest
> >
> > Yes, It does have allot to do with diplexing 1000 KHz and
> > 890 KHz off the same tower.
>
> I've never had problems with mixing products on same tower
> installs. They occur with regularity on reasonably close
> staitons on different towers.
>
Well, you can have intermod and harmonic mixing in the transmitter, in the reciever, or in a third object that reradiates the product.
Let's take the Arlington Heights transmitter site of 92.7, 103.1 and 106.7 I got a call from one of the guys at the local FCC field office one day, he had just gotten a call from the FAA. Seems that there was an objectionable product at 120 point something and it was parked on O'Hare's ATC frequency. A fast call was made to Dave Dybas over at Salem, who had gotten an almost identical call earlier that day. We did the math and found that a combination of our various frequencies did indeed work out to the frequency they said it did. Since you don't screw around with the FAA and the FCC was asking us to act quickly, we did. A set of cavity filters was installed on our stations, one on each, and this did get rid of some harmonics, but not the spur that was causing the concern. It turns out that the mix product was occurring in the reciever in the area, over the area actually. The tuning of the filters was personally reviewed by Tom Silliman of ERI, who also presented an extensive talk omn the subject. This and some great spectrum analyzer work by Mike McCarthy and we were able to prove to the feds that we had not only done everything we could and that the harmonic suppression was well below -80dBc, but that the interference was not being produced at our site.
We assumed that someone was getting into someone else's transmitter. This turned out not to be the case. Never assume anything that you haven;t confirmed yourself!
--Paul
> > Yes, It does have allot to do with diplexing 1000 KHz and
> > 890 KHz off the same tower.
>
> I've never had problems with mixing products on same tower
> installs. They occur with regularity on reasonably close
> staitons on different towers.
>
Well, you can have intermod and harmonic mixing in the transmitter, in the reciever, or in a third object that reradiates the product.
Let's take the Arlington Heights transmitter site of 92.7, 103.1 and 106.7 I got a call from one of the guys at the local FCC field office one day, he had just gotten a call from the FAA. Seems that there was an objectionable product at 120 point something and it was parked on O'Hare's ATC frequency. A fast call was made to Dave Dybas over at Salem, who had gotten an almost identical call earlier that day. We did the math and found that a combination of our various frequencies did indeed work out to the frequency they said it did. Since you don't screw around with the FAA and the FCC was asking us to act quickly, we did. A set of cavity filters was installed on our stations, one on each, and this did get rid of some harmonics, but not the spur that was causing the concern. It turns out that the mix product was occurring in the reciever in the area, over the area actually. The tuning of the filters was personally reviewed by Tom Silliman of ERI, who also presented an extensive talk omn the subject. This and some great spectrum analyzer work by Mike McCarthy and we were able to prove to the feds that we had not only done everything we could and that the harmonic suppression was well below -80dBc, but that the interference was not being produced at our site.
We assumed that someone was getting into someone else's transmitter. This turned out not to be the case. Never assume anything that you haven;t confirmed yourself!
--Paul