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Air Traffic Monitoring => Feed Setup Pictures => Topic started by: SoCal Pilot on May 03, 2012, 01:47:42 AM

Title: Palomar Tower Feed - Setup Photos - "KCRQ2"
Post by: SoCal Pilot on May 03, 2012, 01:47:42 AM
New additional feed for Palomar Tower, KCRQ, in Carlsbad, CA.

- Uniden BC-355C hard-wired to computer power supply and installed in upper drive bay.
- Installed female antenna connection to computer chassis.
- Custom built 1/4-wave antenna tuned to 118.600 MHz.

Title: Re: Palomar Tower Feed - Setup Photos - "KCRQ2"
Post by: tecmah on March 19, 2013, 07:17:53 PM
Great ant installation. I would like to duplicate. Did you ground your ant? How did you fix the ant to the pvc elbow?
Title: Re: Palomar Tower Feed - Setup Photos - "KCRQ2"
Post by: RonR on March 20, 2013, 09:03:02 AM
Nice setup!  Great idea putting the radio in a PC tower...From the pics it looks like you bought the PC with the radio already built in to it  :-)
Title: Re: Palomar Tower Feed - Setup Photos - "KCRQ2"
Post by: SoCal Pilot on March 20, 2013, 12:34:49 PM
Thanks for the positive feedback.  The antenna I guess is technically grounded to the computer chassis.  I am actually glad you asked because that might explain the occasional background noise I hear.  I guess I am getting some kind of a ground loop.  The female coax connection mounted to the back of the PC isn't insulated.  Hmmm.

As for the pvc elbow, the antenna is just seated in the end with the tension of the coax holding it in place.
Title: Re: Palomar Tower Feed - Setup Photos - "KCRQ2"
Post by: InterpreDemon on March 20, 2013, 06:49:41 PM
No, you want the "F" bulkhead connector grounded just as it is, and make sure the radio is, too. If you have not already secured it with a screw through the tray side plate into the LH mobile mount hole, you should. If you can't, you should at the very least run a pigtail from one of those mount holes to the computer chassis, the shorter and thicker the better.

More likely your RF noise is riding in on the audio cable, which is running right over all those nice, harmonic generating digital circuits. I've seen that problem with the 355's in the past, they have poor RF decoupling on that audio out jack and any cable plugged into it acts like an antenna and brings it right on in. I would snap a ferrite bead (pick them up at Radio Shack) over that cable as close to the back of the scanner as possible, in fact you should loop the audio cable through it a couple times.
Title: Re: Palomar Tower Feed - Setup Photos - "KCRQ2"
Post by: SoCal Pilot on March 21, 2013, 12:04:13 AM
Thanks for the tip on the audio cable. I will definitely do that.

What is puzzling to me though is that the noise I hear occasionally will break the squelch. I didn't seem to notice it when I first setup the unit. Now it seems prevalent. You hear it more on the weaker signals and almost always hear it behind the tower audio.

KCRQ tower #2 feed

Any feedback and/or tips appreciated.
Title: Re: Palomar Tower Feed - Setup Photos - "KCRQ2"
Post by: InterpreDemon on March 21, 2013, 12:55:52 PM
Where are you getting power for the scanner? I forgot to tell that that cable should have a bead on it, too. Inside the computer is a pretty harsh environment and I think there is at least a 75% chance that is where it is coming from. I assume you do NOT use this computer for anything else? I would also NOT power the radio from the computer switching supply, at least not without a robust RFI filter, like a Corcom ( ). They are designed for line voltage but work fine for DC, and I always use them on the output of any switching supply that is powering radios. You only need to use one leg to filter the V+, V- and cable shield being to the case and ground, so one COrcom can filter two power supplies as shown in the photo below, where we have twenty radios and six busy servers in one cabinet... it doesn't get more harsh than that.

In any event the first test is to power the radio directly, unplug the audio out so you can hear the speaker, turn off the host computer and see if you still hear the interference. Obviously if it is a workstation you would hear sound related to your activity, or if you turn the monitor on and off, etc. I have a monitor with a power supply that throws stuff out around 129.4 when it is on, and that's radiating out to the antenna 30' above. With your attic installation you could be getting crap from anywhere such as other computers in the house, your WIFI... that reminds me... if you have a WIFI access point shut that down. I had one on my tower that was throwing in random crap, ramped up when a device was connected, and it had been so many years I had forgotten I had the damn thing up there. It drove me nuts for weeks until its power supply failed (which I didn't notice at the time) and the noise mysteriously went away. I assumed it was something in the neighborhood and that was that.

When I finally noticed the AP was out (I have two, one in the basement and one on the tower, so I didn't notice it at first) and diagnosed to the power supply, I happened to be listening to my feed when the power was restored to the AP and presto... the noise was back. I relocated the outdoor AP and the problem was resolved. So the lesson is, it can take time, perseverance and sometimes a bit of luck to track these things down.