APRS Madness Part 2: Height helps… sometimes….

Posted on Posted in Ham Radio, Tech

So in Part 1 of my foray into APRS, I setup an APRS iGate and came to the conclusion that I needed to gain some height to make this thing work. And seeing as I work as a radio engineer and thus have access to towers, I decided to try it out.

Outside of my office, we have a 120 ft tower that houses STL gear and a few auxiliary FM antennas. One of the FM bays on the tower is no longer in use and is used an FM receive antenna. This is routed to my office where I have a modulation monitor and FM tuner hooked up. This antenna is 85 ft up the tower and receives excellently. So, I tapped into this and attached another RadioShack scanner to a computer in my office.

In theory, this should blow the smoke out of my N9TAX Slim-Jim, right? Well, not so much…

If you compare the stations heard in the last six weeks between the iGate at my office and the iGate at my house, my home iGate, which is only 25 feet off the ground on an indoor antenna hears way more. Why would that be?

A tower crew working on the 120 ft tower at my office a few weeks ago.
A tower crew working on the 120 ft tower at my office a few weeks ago.

There are two explanations I can come up with. As mentioned, there is some Microwave STL gear on this tower… in the order of 5 STL dishes in the 950 MHz band. While that wouldn’t effect APRS on 144.390 MHz, it could certainly produce noise that would impede reception. Not helping is a few blocks away is the studios of a competing radio group, and they have STL dishes that point towards my office to get audio to their transmitters northwest of town.

The other possible issue is the fact I’m using an FM antenna bay to receive. This antenna is broad-banded, but is designed to operate between 88-108MHz. While I have put a 2m rig on this antenna before, there is a possibility that being slightly out of tune could hinder reception.

My guess is that it is a combination of the two here. I do have a 2m/440cm J-pole on the tower for my 2m rig (yes, I have one of those at work too) and  I could try that out and see if that helps. But personally I think there is just a lot of RF noise in the vicinity of the office.

So for the time being, my home APRS setup is my primary iGate. That being said there are a group of hams from the area club (me included) that are looking into finding a site for an APRS Digipeter. And perhaps that is the solution. But until then…

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