Inverted V Antenna

(1/1)

James Glenn Jr:
       I have been trying to figure out an HF antenna I can use in my apartment situation.  I have 40' of space in front of my unit.  30' can be played with thus leaving 5' from the side walks.  I will be using an FT-897 and the SGC SG-239 smart tuner.  I have tried a vertical and it picked up S9 noise.  I do not have the room to stretch out a dipole wire.  Currently I am using a 40M hamstick dipole mounted 3' off the ground with minimumal results.  Usually nothing more than several hundred miles.  I was considering an inverted V antenna.  Easy to make and can easily be taken down when not in use.  My plan was to use a Radio Shack tripod on a wood base for stability and a 20' mast (2 x 10').  If I drive a tent stake at 15' in each direction this makes each leg of the antenna 25'.  It would then be fed through an open window via 50 ohm RG-8X coax.  The whole setup is 15' - 20' from the wood apartment building.  Comments are welcome and wanted.

Jim - ke4iza

Bob Lewis:
Jim,

A 50-foot inverted-V is resonant on 9.36MHz and 28.08MHz and will present a roughtly 50 ohm load on only those frequencies. If fed with coax, it will be a good antenna on those frequencies. On any other frequency the SWR on the coax will be very high and so will the loss. To make an all-band antenna you must put the tuner directly at the feed point or use a very low-loss feed line like open wire.

I'll bet that you will find that 40M Hamstick dipole works much better on 40M if you move it from its present 3-foot height to the proposed 20-foot height. In my opinion you are not giving the HamStick dipole a fair chance placing it only 3-feet from the ground. Of course a full sized 40M dipole will work much better if you have the space.

Regardless of what antenna you use, if you want to feed it with coax then you have to make it resonant on the band you want to use. If you want it to be multi-band then you've got to use traps, multiple elements, or "dangles" per Alan's article.

If I were you I'd work on getting the HamStick higher first and see how that does.

Ron Wray:
Like the other fellow said, raise the hamstick dipole & it will work much better. Notwithstanding the (compromised) characteristics of the hamstick itself, that antenna needs to be up around 1/4 wl or more to be effective for anything but local communications. You'll be much better off using ladder line instead of coax if you intend to operate the dipole multiband (due to possibly high line losses related to SWR).

BUT- that S9 noise problem needs to be addressed! Once your antenna is placed at a usable height, it is likely that the noise problem will reappear. Assuming this is locally generated noise, unless you place the noise source in a deep null of a directional antenna you will probably continue to have noise problems. In the end, you may need to resort to a device such as the MFJ-1026 to (attempt to) null out the noise to a tolerable level. I occasionally have S9 power line noise at my QTH & my RX loop plus my MFJ-1026 (plus the NB on my 756 Pro) keeps me on the air until the power company does their thing & fixes the problem.

If you can, track down the noise source & work towards eliminating it. Life is much improved without interference & maybe you can use that vertical again.

73 & GL . . . Ron

Ron Wray:
I notice that you have posted before regarding your antenna installation concerns.  In one such post you indicated that noise was not an issue you wished to discuss- but respectfully, I think that you should give it more thought.  You indicated that using coax to your hamstick (presumably at 3' height) eliminated the noise- but you might have been misled by what you observed, since the hamstick at that height is "working" straight up into the air & since line loss may have been high on your coax if operated on a frequency other than 40 meters.  So sure, the observed noise would be less under such circumstances- but that the same antenna system is all but useless except for local contacts is no surprise either.  That you saw S9 noise on the vertical, and high noise when using twinlead, is IMHO indicative of a problem that's not going to disappear simply by changing your antenna alone.

If it happens that you cannot resolve the noise problem at your apartment complex, try to borrow a MFJ-1026 & see what happens using your vertical or (elevated) hamstick dipole (with the SGC coupler & twinlead).  Try pointing one end (a null) of the hamstick dipole in the direction of the noise- if there is only one noise source that might help.  If all else fails, then maybe you can get on the air by using the vertical or hamstick for transmit in combination with a receive-only noise loop (shielded loop?  K6STI loop?  K9AY loop? . . . scaled down for 40 meters & above) with or without the MFJ-1026.  

If I've understood what you are trying to accomplish and what you are up against regarding noise, I'd say that an inverted vee alone is not the solution you seek.  If you cannot eliminate the noise, you'll probably have to work around it.

73 . . . Ron

Cecil A. Moore:
It appears to me that a magnetic loop antenna at 20 ft. is just about the only rational solution to your problems. 73, Cecil, W5DXP

Navigation

[0] Message Index