Random length long wire antenna

[pintopete]

I put up a random length long wire antenna in my yard that is about 86 feet long and 23 feet above the ground.  It ended up to be 86 feet because that was how far an available tree is from the house.  The antenna seems to receive well.  The quirks are that with my Johnson Matchbox it will not tune down quite as close to 1:1 on 80 meters as I would like.  Also there is enough RF in the shack to burn you quite effectively.  Does anyone have any ideas especially for the RF issue.  I have read some articles on this subject. 

 http://www.aa5tb.com/coupler3.html

Will this type of device help with the RF issues?  Will this affect my ability to tune the antenna for 10 - 80?  Thanks, Peter.  KC2RBX

[Jim KF2SY]

Go in your junk box and take about 33 feet of insulated
wire and tie it to your matchbox ground.  This is a counter poise. Run the wire around the baseboard of your room/shack.  Lots and lots written about counterpoise on the web.  Sumptin quick to try....

Jim

[AF9J]

Hi Pete,

Due to my living situations, I've used random wires for years.  Like Jim said, use a counterpoise.  A typical counterpoise, is a 1/4 wavelength at the freq. you are operating.  But in the case of your random wire, this may not be the best solution, since it may radiate better than your random wire on 80m.  In my personal experience, a good starting point would about 40 feet in your situation.  If you're only going to do 75m, like Jim said, 33 feet would electically give you (sort of) a 1/2 wave, off-center fed dipole.  For better effciency with the counterpoise, you can build or buy (the MFJ Artificial Ground) a counterpoise tuner. I use one, and it has helped my antenna efficiency a bit.   

RF feedback-wise:  I've been dealing off and on with RF Feedback issues for years, with endfeds.  A counterpoise will help some of your RF feed back issues.  Another thing that will help, is a current choke (basically several turns of coiled Coax, at the connector that's at the transmitter end - snap on ferrites, or an iron core makes it more effective) at the feed from your transmitter to the matchbox.  If your matchbox doesn't have a balun, a 4 to 1 balun will help impedancewise with endfed random wires, and also help a little bit with preventing some RF feedback.  I know a fair amount of portable operators that use them with decent results.   Also, as much as possible,try to ground your rigs.  As it is, you may never rid yourself of RF Feedback.  I have chronic problems with RF feedback, on some 40m frequencies.

The matching device you looked at, is mainly for endfed halfwave antennas, which typically have a very high impedance.  They will only help your impedance situation a little bit.  A counterpoise will help you much more.  Also, realize that with your antenna only being about 20 feet off the ground, it won't be a DX machine, due to it's high takeoff angle for RF.  Once in a while, you may work the Rockies or the West Coast on 80m, but your more typical distance will be out to about 300-400 miles. 

73,
Ellen - AF9J

[The Slab Bacon]

Here we go again......................  and end fed antenna is a tough S.O.B. to tame. Your complaints of RF in the shack are to be expected and tough to kill unless the system is set up properly.

The formost and most important item is to have the matching device at the antenna's feedpoint and a good ground / ground system at the feedpoint as well. Trying to feed a random wire with coax and use a tuner in the shack is pretty tough to do, and just about impossible to keep the RF where you want it.

You absolutely have to have the matching device / tuner at the feedpoint of the antenna. You must also have a good ground right there as well. A counterpoise, like Jim said will help, but a good ground is essential if you want it right. With the matching device at he feedpoint, you can run any length of coax that you want to the transmitter, since the matching device will be showing the feedline a 50 ohm match.

Keep in mind that the antenna starts at the random wire input on the tuner. So it is supposed to radiate. If that starting point is in the shack, it doesnt take a rocket scientist to figure out that your rig is right next to the antenna. Also, depending on the length of your "random wire", you could possibly be feeding it right at a current node, putting the strongest point of radiation right next to your rig.

There are several on here that I have worked on 75 and 160 using endfeds and doing a great job with them. BUT............................ they have installed them properly. Having the matching device at the feedpoint and a GOOD ground for that device is an absolute necessity.

You may want to consider a balanced antenna (dipole, inverted V, etc) instead as operating parameters are by far less stringent for good operation.

                                                                                The Slab Bacon

[AF9J]

Understood Frank,

But my living situation still precludes using a balanced antenna.  The last one I expirimented with (basically what I'd call a loopy dipole [2 endfed loops for each leg, fed with balanced line]) was too compact for where I live (I had to configure each dipole leg around my balcony), and was a poor performer on all but the highest bands, in spite of the fact that I used over 130 feet of wire.  I wish I could get away with putting up a 1/4 wave endfed (tuned for 1850 kc or so), like I had back in the mid-late 90s.  It was not so good on 40, but it ripped on 160, through 10.   Yeah, it had some RF Feedback issues on 15m, but unless you decouple the feedline from an endfed (almost impossible to do with a short coax feed [even using a big honking current balun - mine is 10 turns around a a big, chunky iron core] to the T-match), and really have a good ground ( hard to do when you live on the 2nd floor), you accept it as the nature of the beast.

73,
Ellen - AF9J

[KC4KFC]

Are you feeding with ladder line?  I've used end fed antennas that worked well multi-band but they may have been cut 1/4 wave. So in your case, a 65 ft wire fed with ladder line, one side left unconnected at the top, would tune fine on 40 and up.  To tune 80 meters would need twice the wire, if I recall correctly.

Mark

[pintopete]

I think what I should do is first finish setting up my shack.  I have been working on making a bench with a shelf etc.  I have been waiting for the polyurethane to harden up before I put my big heavy tube rigs on it.  After that I planned to set up a good ground system using a ground bus from an electrical panel to which I will attach all my rig grounds and then carry the ground over to the house ground system. 

After that I should try to find a way to put up some really good center fed dipole and just use the random wire as an antenna for my old Hallicrafeers receivers which are just for fun.  Some of my new buddies with lots of ham experience are going to come and help me look at potential locations for a dipole. 

Thanks for all the help, Peter  KC2RBX.

[The Slab Bacon]

  After that I planned to set up a good ground system using a ground bus from an electrical panel to which I will attach all my rig grounds and then carry the ground over to the house ground system. 

I guess I should have clarified things better. Your house ground is ok for lightning and shock protection, but not for RFI.  When I refer to a ground for your antenna system, I'm refering to RF ground. Your house ground system is a DC ground, but seldom ever an RF ground. If the length of wire from the item you want to ground is more that 1/4 wavelength from the actual ground point, you are are NOT at RF ground potential. Just keep this in mind when designing your new shack.

                                                                                         The Slab Bacon

[Ed-VA3ES]

Back in the mid-'90's, I used an End-Fed Zepp, 133' long, fed with about 30' of 450 ohm line.   At the antenna, only one side of the line was connected.

It worked very well on 80 and 40 (so well, I regularly worked G stations in the 80M DX window) and decently on 20 and up.  It performed fair to OK on 160.  My tuner was (is) a Dentron Super Tuner.   No major RF problems in the shack, except for a telephone, and the upstairs TV, both solved with RF chokes. 

My RF ground consisted of several 10' ground rods driven into the backyard, plus my entire cold-water system, which was  connected to and had continuity to the main water main in the street.

[N0BST]

Pete- I've got a similar situation to yours, though fortunately I'm able to operate my rig from the basement, right close to ground.  I'd loaded the antenna as best I could with the tuner (a Dentron with series L and parallel C), but noticed the variable cap always wanted to be fully meshed.  I discovered a 400pf doorknob cap in my junk box and put that across the output of the tuner and that allowed me to get a closer match.  300pf would have been better as now the cap runs with the plates fully open.  This was for 80m.  I'd have to remove that cap for operating the higher bands.  My antenna is way too close to the ground for a good signal, but it's what I was able to cobble together to get on the air.  Hopefully I'll get a used electric pole to string an inverted-V from in the near future.

Scott Todd

[WA1GFZ]

Try a Center fed inverted L. Take the other side of the feed line and attach a vertical lead for as long as you can make it. Closer you get to 80 feet the better the balance. Even a Vee on its side will work.
I'v used an 80 meter lazy Vee and it works ans is balanced. End fed burns your lips when you close talk the mic. On CW tingles the fingers.

[WU2D]

Pete, That is a good run.
My vote is to turn it into a conventional inverted L. This will allow you to put a ground right at the feed point, killing the RF in the shack. Coax would go from the remote tuner back to the shack, whereever it is. I would suggest a single ground rod and a buried 65 ft counterpoise wire which runs along the length of the antenna as a start.

86 + 23 = 109 ft total. This is a very good length for a conventional base load match for 160M and fairly high voltage L-match feed for 75M. 

The match can be as simple as 30 turns of copper tubing 4" in diameter supported in a few places against a 300 pF - 500 pF motorized cap to ground. You could determine the match empirically with a clip and then graduate to a relay system for changing bands. This setup should tune 160M - 20M without much trouble.

Good luck!

Mike WU2D

[WA1GFZ]

yup mike that would put you on 160m but you then need a ground system

[WU2D]

Frank is right, but half an antenna on 160M is better than no antenna! You will get out some. The vertical portion is somewhat short to be really effective on 160M. Marconi Antennas can be made to work very efficiently and the ground system can be "improved" over time.

I have found by expermenting with lowfer antennas that the best way to determine how well you are doing in the ground department with an antenna like this is to get an old fashioned RF Ammeter like grampa used.

Insert the ammeter at the point where the loading coil meets antenna. 

Match the antenna with the tuner using the SWR meter like normal and then take a baseline antenna current reading.

Now start playing with the ground system and the feedpoint - try off center and center feeding. Add ground rods and radials and strap the thing to your cold water pipe! Try everything. If the current goes up - that is a good thing.

Mike WU2D