HFU HF Underground
Technical Topics => Equipment => Topic started by: ChrisSmolinski on July 20, 2018, 2001 UTC
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I've made a few changes to my antennas, and thought I would share them and the results:
I have two new beverages, one runs west-south-west about 250 ft, the other nearly due south, about 300 ft long. This is in addition to the northeast beverage that is 500 ft long.
Initially these beverages were not terminated. I left the NE beverage unterminated as I wanted a less directional pickup pattern, especially as I use it for DGPS.
I then terminated the south beverage. I left it connected to the SDR and recording while I connected the termination resistor, so I could see the results. MW stations to my north were attenuated about 11 dB on average compared to unterminated. Some less, and a few more, nearby 1280 WHVR in Hanover PA by 25 dB or so. Stations to the south were mostly unaffected, maybe a dB increase in signal, but this could have been imaginary. This antenna runs across my backyard, then down a hill through a path cleared in brush, ending at a small stream. The soil is very damp and rich where the ground rod is located, probably low resistance/impedance. I initially used a 240 ohm termination resistor. I changed to something closer to 400 ohms, since in theory that was closer to the impedance of a beverage at this height, but the F/B ratio got worse, so I went back to 240 ohms.
This led to me terminate the other two beverages. The 500 ft NE antenna also terminates in a damp marshy area. I do notice a better front to back ratio with it grounded, although perhaps not quite as much as with the south beverage. However I am using the 400 ohm resistor previously used on the south beverage, I need to switch to 240 ohms and see if that improves things. While going back to the end of the antenna, I noticed that a tree had fallen down in the woods, pinning the beverage wire (which is insulated) to the ground. I decided cutting and splicing the wire was easier than cutting and removing the tree.
The WSW antenna runs along the driveway, and stops shortly before the road. That part of the yard is mostly rock with a very thin layer of dirt (which could never be confused for topsoil). The ground rod is barely two feed in the ground there, and I did not notice any change in F/B ratio when connecting it. We're going to get a week of rain, and I may try relocating the ground rod slightly to a location that is less rocky, and maybe I can get it further in the ground, but I am skeptical.
My primary motivation for installing the south beverage was for receiving South American pirates. I figured even if it failed at that, it would be useful on MW, both as a stand alone antenna, and for phasing with the other antennas. This isn't the best time of the year for catching the Latin American pirates on 43 meters, but the few nights they have been on, the south beverage has produced a better SNR signal vs the sky loop or 40m dipole. It is also quite directional on MW, it substantially reduces the strength of the Hudson County TIS station on 1710. Now I just need a pirate south of me to come on the air.
I ran the WSW beverage because it was a fairly easy run, I didn't have to clear any brush. Just string the antenna up along some evergreeen trees. I don't use it very often yet, I may use it for phasing, or perhaps stand alone if I can get a decent ground installed for the termination, and it gets a better F/B ratio.
It's great fun to switch between antennas on a given MW channel, and hear a different station, depending on the antenna.
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Well, with all the antenna real estate that you have, ever try the WOG (Wire On Ground.)? JTA has tried that with decent results and less noise. I have rolls of trashed RG-11 cable here that I use to make various antennas with, and plan to make a WOG out of one of those rolls. No longer good for CATV anymore, due to water contamination, but those long lengths of rigid outer aluminum shielding work fine as various antennas. Yep... Practically nothing goes to waste here. And, if you want solid copper wire that's bigger than #10AWG, that's what the center conductor is in these RG-11's. Albeit, it takes some bit of work to get at that. (Damn, I'm cheap.)
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You might try a variable resistor to narrow down the best range for termination, but that brings up how do you see the smeter from where the pot is?
On the "ground rod in rock", lay the whole thing on its side in the layer of dirt and bury it and see how that works out.