RF in the Shack

[koØm]

Once, I had a forty foot tower topped with an eight element Yagi, a tripod mounted on the roof with a four element Yagi and, a random length wire connected to my Dentron Super Tuner Plus, that was "yesterday". Today, I am in a third floor apartment, been here since 1995. For 16 straight years, the Maintenance Manager would terminate "With Extreme Prejudice" any attempt to attach or extend a wire out of my apartment to use as an antenna. Finally, that fellow got promoted to the home office in Dallas and a new crew took over.

With the new crew came the opportunity for me to string an antenna, the new manager even allowed me access to the roof! Hastily, I threw together a OCF Dipole of random length #15 coated magnet wire. The antenna is fed with 75 ohm flat double lead, one leg is orientated horizontally in an East-West direction while the other leg comes off the dog-bone insulator vertically for six feet then goes horizontal on the roof; both ends are supported by insulated bog-bones. Picture an "L" that is thirty-five feet above ground (one leg higher than the other). All equipment chassis have an individual ground connection wired commonly to the metal frame of the sliding window; outside, there is a piece of #15 wire connected to frame of the window that drops three stories to a grounding rod.

My Station (and the rest of the household electronics) is situated on the same plane as my East-West leg and my radio is directly under my North-South leg. With the Dentron, I can tune 75, 40, 20, and, 10 meters. Everything is cool until I use 10 meters, it knocks the USB out on the laptop and freezes the dual core desktop computer; this is at QRP levels on PSK-31. I run power on 40 meters with no problems.

I guess I should say the Shack is in the RF Field.

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[W9JEF]

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I also lived in a third story apartment (but had no access to the roof).
I end fed a quarter wave wire on 80 meters against a counterpoise.

To effect a low impedance ground on 10 meters,
try connecting an 8-foot wire to your station ground,
with the other end extended clear of conductive material
(as if it were an antenna).

[WØTKX]

Yes, a wire used as an "artificial ground" cut to the right length(s) should work well. A couple of wires cut for the different parts of the band might be a good idea, 10 is a big band. The MFJ-934 "ground tuner" or something similar could work for you... as would an extra tuner you may already have used in "longwire mode" on the previously mentioned wires.

Mind the high voltages on those wire ends. :)

[koØm]

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I also lived in a third story apartment (but had no access to the roof).
I end fed a quarter wave wire on 80 meters against a counterpoise.


To effect a low impedance ground on 10 meters,
try connecting an 8-foot wire to your station ground,
with the other end extended clear of conductive material
(as if it were an antenna).

That's easy enough to try; radials cut for each band .

Yes, a wire used as an "artificial ground" cut to the right length(s) should work well. A couple of wires cut for the different parts of the band might be a good idea, 10 is a big band. The MFJ-934 "ground tuner" or something similar could work for you... as would an extra tuner you may already have used in "longwire mode" on the previously mentioned wires.


Mind the high voltages on those wire ends.

All equipment chassis have an individual ground connection wired commonly to the metal frame of the sliding window; outside, there is a piece of #15 wire connected to frame of the window that drops three stories to a grounding rod.

So, if I could, I would be putting an antenna tuner in the ground leg of the system?


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[W9JEF]

That's easy enough to try; radials cut for each band .










So, if I could, I would be putting an antenna tuner in the ground leg of the system?


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The idea is to tune your ground lead to make it purely resistive.

A variable capacitor in series might do it.

Depending on the length of the ground lead,

you may need to add some series inductance.

The idea to form a series resonant path (low impedance) to ground. :)

[kb2vxa]

That's not how common point grounding is done, each ground wire goes individually to the earthing rod. It's not for mitigating RF in the shack, but rather for preventing huge currents from a lightning strike causing large potentials, sometimes in the kilovolt range from appearing between equipment, Ohm's Law.

Since there's no such thing as RF ground unless we're talking about an antenna counterpoise, an artificial ground suggested above works well, but you can avoid the cut and try method and using one for each band with an artificial ground tuner. They're available from several sources in several power and price ranges, all you have to do is look them up on line. They may be used to tune a counterpoise thrown across the floor or a ground wire to an earthing rod. Since you have wires out the window, and common point grounding is just a bit more than necessary I offer a possible solution.

First, the only common point ground needed for lightning protection in your case is running two ground wires, one from a shack common ground from which you've disconnected the window frame, you don't need it, and the other from an arc plug or spark gap arrestor where the transmission line enters the house, both to the earthing rod, preferably several connected together and the leads to the closest one. Where the shack leads come together and connect to the earthing wire is the place to put the tuner, but you knew that. (;->)

Since the antenna runs over the house one usually suspects radiation from it causes a mess but it ain't necessarily so, a friend had part of a backward looking inverted L barely clearing the roof with no problems at the 150W AM carrier level. It's one of those infinite number of variables things so if the tuner doesn't fix the problem I don't know what more I can tell you other than cover your house in grounded copper screening, a Faraday cage. Just don't forget to cut holes for the doors, leave the screen over the windows so bugs don't fly in.

Here's a rather funny example of "he should have known better". Another friend had a ground mounted vertical in his postage stamp yard that worked just fine with no neighbor complaints. He should have left well enough alone but no, he wanted to be an alligator, all mouth and no ears. He bought at no small expense the latest and greatest with all the bells and whistles "full gallon" amp, and that's when the trouble started. He was left with a boat anchor of modern vintage, don't know what he did with it but I can guess where the neighbors told him to put it.

[W9JEF]

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What is a "ground tuner"--other than a series-tuned L/C circuit?

You can save yourself a bundle by using a junk box variable,

and winding your own coil (cut and try). :)

[NY4Q]

Hastily, I threw together a OCF Dipole of random length #15 coated magnet wire.

Rather than chase your tail with "try this" and "try thats", and since you now have full access to the roof (at least until your current setup gets into enough folks' stereos, TVs, toasters, etc.), I'd spend some time on the roof and visualize a better antenna system.

Get up there and take a few measurements, and build something that will work best for the setting.

And CONGRATS on getting that new crew!

[WØTKX]

^^^ This.

I had a buddy stuck on a 5th floor apartment who used a spare tuner to "tune" his RF ground wire running along his hallway. He was able to kill most of the RF goblins on the HF bands this way, even at 100 watts. And yes, you can make your own, as a regular antenna tuner is overkill. I personally dislike the badly named "counterpoise" label, but it is what it is.

I got some RF in my current shack on 12 meters till I screwed around with a (specific) wire length attached to the first ground rod outside my window.

Figured you might have an extra tuner laying around, or could borrow one. Maybe you have an antenna analyzer available? If so, you can cut the wire just right and/or find a good capacitor value to use as well.

[NQ6U]

I hate it when that bastid gets into my shack.