I spent a modest amount of time operating this week as K2B the www.13colonies.info call sign for the state of Virginia. There were four of us operating from VA. I spent about 9 hours operating and made 775 contacts. I had about four of those hours where I was making about 70 contacts an hour or more. And about 5 hours that were much slower paced. The conditions were rough this week for me. There was a ton of QSB(fading of signals on the band) and my noise floor at times was higher than the signals of over half of the stations I was working.
I learned something very quickly, I was being heard a lot better than I was able to receive. I operated my Flex 5000A at it's full output, 100W, into a 17' tall vertical antenna on the roof of my office at work. The roof is metal underneath a layer of rubber and gravel, it's called a ballasted roof structure, the gravel holds the rubber down on top of the insulation which is on top of the corrugated steel roof. I have braided grounding straps running from the antenna grounding systems and the Flat roof antenna mounting structures. So the idea is that the metal in the roof will act as a counterpoise to the antenna system, or a ground plane if you like.
I had been observing a high noise floor on 20m for a few weeks. With that in mind I bought a piece of 3/4"x6' copper tubing, and some 12"x1" braided grounding straps. On July 4th, as you see below, I used those supplies to construct a station grounding system. It's basically an RF/DC ground. I pounded the tubing flat with a dead blow hammer, then drilled six holes in that spaced out near where the grounds are for the various pieces of equipment on the shack desk have their ground terminals. I ran the braid from the equipment, F5K, Two Power supplies, an Icom 746, and an MFJ 946 antenna tuner, as well as my little IC-2720 V/U rig. This helped a bunch with the noise floor, lowering it about 5-10dB. So at this point I got an S5 or so noise floor.
But my receive was still not as good as my transmit, in fact, my transmit efficiency got even better, which sort of compounded the problem. The problem was that guys were hearing me S9 and S9+ and I was hearing them in the noise. I think there are a few problems going on. Capture area, I think maybe this antenna is just too small to capture a lot of signal, even though it is about 1/4 wave antenna, it's just not a lot of capture area, a half wave dipole would be twice as much. Another problem I think is the vertical polarization. I am in an industrial area, and a lot of the noise I get is vertically polarized, just wait until the behemoth across the street goes on line(more on that another time). Also, I think that I still have a bit of a grounding problem.
It is important to be able to receive when you are running a contest or special event. Just being heard is not enough. With 100w more people could hear me than I could hear, imagine if I had 1500watts and a receive problem! That is where the classic Alligator sation comes from, all mouth no ears. If you can't hear them you can't work them, it's a problem, and a problem that makes you look like an appliance operator instead of a real radio station operator that understands his equipment.
So what to do about it? Well, that's for another day, I am still thinking about that. The obvious(to me) answer would to be to get one of my beloved balance line fed doublets up in the air. But my QTH presents some challenges with that. Flat roof with no existing structure to get a horizontal wire antenna up. Oh, and a limited budget, and limited lattitude.( I don't think my boss will go for a SteppIR on a roof mounted tower)
Any ideas? feel free to comment and help me brainstorm.
73
AJ4TW
I learned something very quickly, I was being heard a lot better than I was able to receive. I operated my Flex 5000A at it's full output, 100W, into a 17' tall vertical antenna on the roof of my office at work. The roof is metal underneath a layer of rubber and gravel, it's called a ballasted roof structure, the gravel holds the rubber down on top of the insulation which is on top of the corrugated steel roof. I have braided grounding straps running from the antenna grounding systems and the Flat roof antenna mounting structures. So the idea is that the metal in the roof will act as a counterpoise to the antenna system, or a ground plane if you like.
I had been observing a high noise floor on 20m for a few weeks. With that in mind I bought a piece of 3/4"x6' copper tubing, and some 12"x1" braided grounding straps. On July 4th, as you see below, I used those supplies to construct a station grounding system. It's basically an RF/DC ground. I pounded the tubing flat with a dead blow hammer, then drilled six holes in that spaced out near where the grounds are for the various pieces of equipment on the shack desk have their ground terminals. I ran the braid from the equipment, F5K, Two Power supplies, an Icom 746, and an MFJ 946 antenna tuner, as well as my little IC-2720 V/U rig. This helped a bunch with the noise floor, lowering it about 5-10dB. So at this point I got an S5 or so noise floor.
But my receive was still not as good as my transmit, in fact, my transmit efficiency got even better, which sort of compounded the problem. The problem was that guys were hearing me S9 and S9+ and I was hearing them in the noise. I think there are a few problems going on. Capture area, I think maybe this antenna is just too small to capture a lot of signal, even though it is about 1/4 wave antenna, it's just not a lot of capture area, a half wave dipole would be twice as much. Another problem I think is the vertical polarization. I am in an industrial area, and a lot of the noise I get is vertically polarized, just wait until the behemoth across the street goes on line(more on that another time). Also, I think that I still have a bit of a grounding problem.
It is important to be able to receive when you are running a contest or special event. Just being heard is not enough. With 100w more people could hear me than I could hear, imagine if I had 1500watts and a receive problem! That is where the classic Alligator sation comes from, all mouth no ears. If you can't hear them you can't work them, it's a problem, and a problem that makes you look like an appliance operator instead of a real radio station operator that understands his equipment.
So what to do about it? Well, that's for another day, I am still thinking about that. The obvious(to me) answer would to be to get one of my beloved balance line fed doublets up in the air. But my QTH presents some challenges with that. Flat roof with no existing structure to get a horizontal wire antenna up. Oh, and a limited budget, and limited lattitude.( I don't think my boss will go for a SteppIR on a roof mounted tower)
Any ideas? feel free to comment and help me brainstorm.
73
AJ4TW
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