Discussion in 'Amplitude Modulation' started by KK4RSV, Apr 25, 2019.
Always brings a smile to my face when that mode is referred to as slopbucket. Thank you!
I ditched coax on my wire antenna about 25 years ago in order to lessen RFI to neighbors.
Back then I was using 1" foamflex right up through a freestanding tower.
It worked, plus I landed up with a feedline doublet combination which worked on 75 with only a balun in the shack to the feeders which ran across the basement with zero problems.
Fast forward to today. Nobody in my neighborhood mentions any type of received interference anymore but I can't hear anything on the low bands unless the telescoping tower is high enough to suspend the balanced wire. This is where people who like to shoot down the so called end fed appliance antennas should be focusing.
The owners of "end fed" are going to receive every single local noise in fine style. Instead you see people arguing Quark theory.
Those antennas actually transmit just fine on at least one band if the installer follows certain rules.
I used that for a while. Pair of roller inductors on a common shaft and a vacuum variable cap. I kept getting these perplexing VSWR readings. I'd be unable to get the rig side of the network down to 50 J0; the vswr would be around 1.2:1 at minimum but at other times it was flat 1:1. The rig didn't care of course neither did the receiver so from a practical point it didn't matter, but I don't like mysteries so I was curious about how I'd randomly see that 1.2:1 minimum on a swr analyzer. I examined the feedline and antenna. Only thing I saw were spider webs on the feedline. I thought perhaps when they get wet they change the dielectric property or something. Eventually I discovered that the problem was only an error in the swr analyzer reading and existed coincident with 20 dB over S9 power line noise. The line noise was so strong, it was coming across the network and affecting the swr analyzer. When I switched to a KW Matchbox the problem (such as it was) vanished because there was no longer a DC path from the balanced line through the Rich Measures network to the coass. While this as I wrote previously wasn't really a big deal, it was instructive: the link stops or attenuates some kinds of RFI that the Measures network did not.
The link tuner is high pass and the Measures tuner is low pass.
DC ground is a big plus in my book. If DC continuity is a problem all it takes are a pair of blocking capacitors as in a Pi-net.
I did not know that and I'll have to look into that. I was always under the impression from somewhere, that the link tuner was also low pass. I guess the architecture of the link across the unbalanced line changes things as opposed to inductors in series with it.
True, but if floating the feedline with a link is a problem you can always attach a pair of static drain chokes to ground at the entrance. I've never bothered with that but I've seen some guys do it. When I'm away from the shack or wx looks ominous I pull my feedline outside and get it away from the entrance. I use banana plugs and jacks. One of the great things about open wire line is what's involved to splice it, or install connectors.
Using the simple DC continuity rule the link would be high pass but in actual practice it's bandpass. An exception would be capacitive coupling between links with harmonics.
This has been educational .I think I'll try a fan dipole running 160,80,40 .I can get the feed about 50 to 60 feet and run a 1:1 balun .
W2WDX what type of balun is yours ?25 ft. of 213 on a 5" form may be a little heavy, could always use a heaver support though.
A 4x4 box with ferrite toroids would be lighter and the box would be used for the center support as well.
There are tons of web sites about baluns and I would like to here from someone who has success running high power AM through them.
Balun Design's 5KW 1:1 model survives most anything I could throw at it.
"most anything". ^^^^
I'm using a 4x4 box and a toroidal choke similar to the Balun Designs 50 ohm 1:1, but mine uses three cores instead of two. I'm using LMR-400 on an inverted-V supported on a mast at the center @60' using the balun as the "center insulator".
The first balun I built was only two cores, but when I took temperature measurements I saw a rise I didn't like. So I took it down and added another core and rewound it; which keeps the balun cool with the high duty-cycle modes (AM) and power levels I like to run (~200W carrier).
This is the original balun which I later added another core and added the 10ga copper-clad for the elements. I did have to find a 4x4 box that was a little deeper to accommodate the three cores.:
Mechanically speaking, not supporting the center on a larger dipole is not the best approach IMO and complicates construction (bigger everything) due to the weight of feedline, which can be substantial once you get up to any beneficial height. I still use 10ga copper-clad steel regardless; while most people don't and do not realize how much weakness on pure copper is created over time with the weight of the copper elements, coax, plus any hardware and a balun. So center support is something I just always do. Even if I only had two trees, I would still run a "messenger line" type support, if just to take the mechanical load of the feeder off the elements.