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KF4VIX
Sun 27th Jul 2014, 03:31
Hey guys. This is my first post. I got my license back in 1998 and piddled around on 2m for a little while, but then life took over and I wasn't really active at all for almost a decade. I'm a police officer, and decided I wanted to get an inexpensive HT to carry with me in the patrol car just to listen to the local guys and see what was going on.

I picked up a 2m/70cm HT and it works very well. But, there is something strange going on that I can't put my finger on. I live 19 miles away from the city that I work in, and that city has several different 2m/70cm repeaters. The most active repeater is a certain 2m repeater, and I can reach it from my house using only the "rubber duck" antenna and 5W. Signal reports are mainly positive from that distance, and to say I'm impressed is an understatement.

Now, here's the dilemma: When I get to work, and turn my HT on in the patrol car, all I get from that repeater's frequency is static when I key the PTT. I thought there was some type of interference from some radio equipment in my patrol car, but testing it out when I wasn't working gave the same results both inside a vehicle, outside a vehicle, and from various locations around the city. I can't "key up" the repeater, and when anyone else is broadcasting, I can't receive it either - it just sounds like loud electronic garble.

So, what gives? How can I TX/RX a repeater 19 miles away on a HT with good results, but I can't use it at all when I'm in the same city, within ~1-3 miles of the repeater itself?

Any ideas or suggestions are appreciated.

Thanks!
-Lee

5B4AJB
Sun 27th Jul 2014, 13:44
Try an external antenna with a small linear amplifier (10-20W) Even if the external antenna is the rubber duck, it should work.

City buildings & reflections make it hard for signals to propagate, especially if you're on lower ground (in a hole).

K7KBN
Sun 27th Jul 2014, 15:20
There can be all sorts of RF noise producers in a city, and it sounds like you've found one or more. Judging from your first post, you don't have the HT turned on until you get to work. Try this: when you start out from home, turn it on. Don't use it while you're driving, but keep an ear busy listening to see just where, in your commute, the noise starts.

But I also note that the problem exists only when that particular repeater is transmitting. That could indicate a problem of front-end overload if the HT can't manage the stronger signal from the repeater at 1~3 miles vs. 19. Might also be some intermod between the repeater and some other strong RF source.

So on your commute (or maybe on a weekend when traffic isn't so much of a bother), take the HT and just make test transmissions every couple of miles and listen to the repeater. See if the problem recurs reliably at a particular location. If it does, put on your detective face and see if there's a noise source somewhere around. You might need a few more receivers to check, but that's the name of the game.

Is there another repeater (ham or not) nearby? And by that I mean nearby as in location AND/OR nearby in frequency.

KF4VIX
Sun 27th Jul 2014, 19:34
There can be all sorts of RF noise producers in a city, and it sounds like you've found one or more. Judging from your first post, you don't have the HT turned on until you get to work. Try this: when you start out from home, turn it on. Don't use it while you're driving, but keep an ear busy listening to see just where, in your commute, the noise starts.

You're right, I usually don't have it on during my commute. But, I did do what you are suggesting one day last week. The repeater was almost full quieting during my commute, until I got just inside the city limits. Strange.



Is there another repeater (ham or not) nearby? And by that I mean nearby as in location AND/OR nearby in frequency.

Yes, there are several (both 2m and 70cm). Just for the sake of explanation, the repeater I'm having trouble with is on 147.210(-). However, there is another repeater in the same city that operates on 145.310(-). Both use a PL of 107.2, and are both operated by the same amateur radio club.

I can reach the .310 repeater while I'm at work just fine, and use it to communicate with my father from time to time. However, I can't reach that same repeater from my house as I can the .210 repeater.

Part of the problem is that I don't know the "exact" geographic location of each of the repeaters, only that they're located "somewhere" in the city. That is why I said I am likely within ~1-3 miles of the repeaters.

Front end overload is something that I thought about, but I don't know of any ways to test that theory, or what to do about it if it turns out to be the case. I'm off work for the next couple of days, but I plan to do some more experimenting to see if I can narrow the interference down to something specific.

Thanks for the reply!
-Lee

KF4VIX
Tue 29th Jul 2014, 04:21
OK, I've figured out the "problem."

Turns out, the repeater that belongs on that frequency is undergoing maintenance, so they're using an alternate repeater on the same frequency - however, the alternate repeater is in a different city that is about 10 miles closer to my house. That explains why I can reach it from my house, but not at work as I would normally be able to.

They're supposed to have the main repeater back up and running in the near future, so all should be back to normal.

K7KBN
Tue 29th Jul 2014, 15:58
Yep, that could do it! The simplest explanation is generally the best one - and involves a lot less noodling to come up with the solution.

Glad things will get better soon!