Little Help with antenna project

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I am building a simple center fed receive antenna using the materials in the picture below. I have it all connected at either hole in the wood block using ring terminals and nuts/bolts. I am not sure how long to make the wire hanging off each end.

I have a ton of #12 THHN laying around so I am using that as my ends. At the moment my plan is to drape the completed antenna over the peak of my garage roof (about 15' high) and run the end to the radio.

I have seen a lot of plans on the net for similar antennas such as the G5RV but that would be too long. Just looking for a little advice to get this up and running for receive of the HF bands etc..

Thanks

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kb1awi

Member
This sounds like your are trying to make a Multinand Antenna for the HF frequency from your mention of the popular G5RV antenna.

Are you going to use this to transmit or just to monitor? To construct a HF dipole from the wire you mention , you have to use the formula to determine the length by:

Length in feet = 468/Mhz = 468/ Frequency. If the resonant frequency you wish to monitor/ transmit is 3.550Mhz, then L= 468/3.55 which is 131.8 feet. If your frequency is around 21.300Mhz ... that comes to 22 feet of wire.

73
de kb1awi

I am building a simple center fed receive antenna using the materials in the picture below. I have it all connected at either hole in the wood block using ring terminals and nuts/bolts. I am not sure how long to make the wire hanging off each end.

I have a ton of #12 THHN laying around so I am using that as my ends. At the moment my plan is to drape the completed antenna over the peak of my garage roof (about 15' high) and run the end to the radio.

I have seen a lot of plans on the net for similar antennas such as the G5RV but that would be too long. Just looking for a little advice to get this up and running for receive of the HF bands etc..

Thanks

Last edited:

k9rzz

Member
The dipole antenna you have described as your project is really a one band antenna, designed to work over maybe 250khz for it's peak performance. For receive, it will work on other frequencies, but not as well. So, pick your favorite band to cut it for and take it from there. How can you optimize it for any other frequency? An antenna tuner would help in most cases. For receive only, you can also disconnect the shield of the coax and just use it as a random wire, or you can short the shield and center together, again to use it as a random wire.

I use one of these little guys in the car when I'm portable:

I just throw 30 or 60 feet of wire up in a tree and tune it for lowest SWR (or best signal for receive). It should work with your antenna too.

Summary, cut your antenna for your favorite band of frequencies and if you're not satisfied with performance on other frequencies, try a small antenna tuner.

jw
k9rzz

prcguy

Member
The secret weapon for making an HF dipole happy as a multiband antenna is to feed it with a balanced feedline like TV twinlead or 450 ohm ladder line. One big problem with operating a coax fed dipole out of resonance is increased loss in the coax over the calculated loss, which can exceed 20dB for a moderate run where you were only expecting a few dB. In other words, when operating a dipole out of resonance fed with balanced line you can almost ignore the feedline loss that would kill the same antenna system fed with coax. TV twinlead solders easily to a PL-259 connector and 450 ohm line is not a problem either. For transmitting you would use a tuner of course and a 1:1 choke balun at the radio/tuner end will help keep the balanced feedline isolated from the grounded radio chassis. When the balanced feedline is truly balanced it will not radiate (very much) and will also not pick up stray crap as the feedline wanders up to the antenna. For HF receive you don't really need a tuner, I use several G5RVs and other balanced feedline antennas and after I tune up for transmitting I really don't see any increase or change in reception. Good luck with your antenna!
prcguy

zz0468

Listening from DC to Daylight
I'd suggest using something other than a wood block for an insulator. PVC plastic tee's are pretty good. The problems is that the wood will get wet, and your "insulator" won't be so much of an insulator anymore.

N1BHH

Member
You have a good idea. You won't really need anything more than a half wave antenna for around 7 Megahertz to give you decent coverage of the High Frequency bands. An antenna tuner is only needed when you want to transmit on a frequency other than the one it is designed to function on. A good source of antenna wealth is found all over the internet. Here is one place to find antenna ideas: http://www.hamuniverse.com/antennas.html
Another great place is found here: http://ac6v.com/antprojects.htm

I'm glad someone is taking the initiative to actually build antennas, instead of buying one of those prefabricated antennas. The G5RV antenna is optimal on 20 meters and is only fair on 40 and 80 meters. I use an extended zepp, center fed with twin lead, to the MFJ945C, on 75 meters, all 170 feet of it. It has slight gain over a dipole due to it's length, and a nice jump in gain at 40 meters.

I simply took an old egg insulator and used that for the center point, stripped the twin lead back a little and soldered the connection good. Had a 1000 foot spool of #16 jacketted wire I bought at Home Depot for such antenna projects. Mine is 40 feet up in the center, one leg is nearly flat while the other leg slopes down toward the corner of the house, only because there are no trees in that direction. It should ideally be a half wave up, but the trees don't grow that high, so I use what I have.