Our entire team visited the site on Sunday. One was the supervisor, one held the ladder, one screwed in the light bulb while three rotated the ladder... LOL.
After a lengthy visit to the site we measured the FM broadcasters on our station antenna up at 85 feet at -1 to -3dBm! We measured VHF paging transmissions at -25dBm. We measured no significant reflected power on the antenna prior to connecting it to the service monitor. Plugging the antenna into the ANT IN on the HP Agilent 8924C I read -76dBm with a span of 2MHz. This is with a 6-cavity Sinclair duplexer and a Angle Linear dual band pass cavity. The symptom is like a blanket has been thrown over the receiver of our MSF 5000 that worked fantastically at its former location. I know enough to run the tests and record the findings but not enough to solve the problem. I honestly don't remember the reading in dBm without anything connected beside the antenna but there were tall spikes all over the screen with a 135MHz span -- we needed to see the broadcast stations and paging transmitters. There appeared to be a small spike on or near our input with this wide span. It wasn't there with a 2MHz or even a 1MHz span.
I received a DCI-146-4H band Pass filter that is quoted at -89dB at 126MHz and the plot shows it out of range for the FM broadcast band. Everything is grounded to a new ground rod with 8ga. multi-strand copper wire. All cables are RG-214 with new crimp N connectors. They average 4' in length and can be shortened once we put in a 19" rack. After speaking with an extremely well respected manufacturer of repeater band pass cavities we learned this morning that we should aim for a 5" length of cable. If that doesn't work we should next try 24".
But are we wasting our time? I simply don't know what more to do. Once adding the DCI band pass filter I will be adding an additional 1.5dB of loss on top of the cable loss, the duplexer and the Angle Linear (he makes good stuff) should I even think of a preamp? The Angle Linear was received with a 17dB preamp and I think that may be too hot. Currently we can hear stations at our coverage borders that previously were workable but have now dropped to marginal at best. Again referring back to a conversation with an extremely well respected manufacturer he suggested that once everything is tuned correctly we should have at least a 20dB return loss. Once achieving this a 17dB preamp is not too hot. First things first.
But the overall point/question remains the same. Should I change all of the interconnect cables to 1/4" SuperFlex; the RG-214 is spec'd at only 95% braid for both Belden and Times Microwave (we have Belden deployed and a roll of Times Microwave RG-214
We are NOT
running LMR 400 anywhere!!! We're indoors and maybe we should since TM is quoted as agreeing that outside LMR 400 does not hold up because of dissimilar metals versus indoors and no corrosion potential. TM LMR 400 is quoted at >90dB rejection of ingress/egress and >180dB of crosstalk. But lets NOT go down this road. We are NOT running LMR 400. The question is whether or not the interference is coming in by way of the antenna (using Andrews 1/2" hard line (LDF4-50) or if the 95% braid of the inter-connect cables is letting it in. Once again referring to a leading manufacturer LMR 400 is quite usable for inter-connect cabling. Please, please, please, let's not go there
RG-214 is working fine but the length is way off. 5" or 24".
Quite humbly I don't know what to do
I am going to follow the directions I have been given and I offer this message as a follow-up with a hand out for more suggestions. I am not too proud to admit that I don't know enough and that I am struggling through.