Can I use a 40 meter dipole on 20 and 15 meters?
I'm looking at the Force 12 "Sigma 40" 40 meter vertical diplole...
Presumably, this antenna is a half wavelength at 40 meters, so with an antenna tuner (or not) would I be able to use it on 20 meters? Also, since 15 meters is a third harmonic, could I use this antenna on 15 meters?
Also, could I listen (not transmit) to 75 meters?
Many thanks in advance!
The antenna should work fine on 15 meters as a 3/2 wave antenna. However, on 20 meters or 10 meters the antenna is going to present a very high impedance to a coaxial cable feedline. You might be able to use an antenna tuner to "match" your transmitter to whatever impedance the feedline presents at the transmitter end. However, the line losses in the coaxial cable will definitely be considerably higher than when operated on 40 or 15 meters.
As for receiving on 80 meters, it should work fairly well. But, to transmit using the antenna you will definitely need to use an antenna tuner and the performance may be anything from OK to really dismal. You just will have to try to load the antenna with your tuner/transmitter arrangement and see what happens.
I've tried a horizontal wire 40m dipole. I could tune it with a tuner, but it was worse than dismal on 80m and 20m. Very good on 15m, and great on 40m (or it wouldn't be a 40m dipole). It was also pretty good with a tuner on 30m and fair on 17m. Not bad for a single wire antenna. The math should be the same with a vertical dipole.
Edit: Since this vertical dipole is only 24 feet tall, I'm not so sure how it will perform on other bands (or even 40m). That is shortened.
Edit #2: $749.00?!
Last edited by WW3QB; 04-29-2009 at 12:11 AM.
Reason: Price shock
Thanks guys! Yeah, that price is a bit high, reviews at eHam say guys are paying about $488
Thanks again, guys!
Yikes, Thats a lotta $$$ !
You can homebrew a 40M vertical for WAY less $$$
That sigma40 will work "OK" anywhere above 40M- The issue will be a high VSWR causing extra loss in the coax. The antenna is already "short" on 40M,but not too bad, 80 and 160 will be a exercise in frustration.
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Originally Posted by WA9CWX
P. T. Barnum reigns supreme!
For 1/10th of the cost, an ARRL Antenna Book (and some of your time) is a wise investment.
Last edited by KJ3N; 04-29-2009 at 01:50 PM.
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Unless you just like weird antennas, you can get a Butternut HF6V for a little less money and it's only 26 feet tall (2 feet higher than the Sigma). It will work 80 through 6 meters and my experience with that particular antenna has been very good. The only difference is you will need to put down a reasonable number of radials to make it work well. The best part is you won't need a tuner.
Originally Posted by W6IRE
I'm sorry you don't have the experience or understanding to realize that others possess a skill set that you seem to dismiss as fantastical.
The best part is that it doesn't cost $500 ! ! ! Does it ?
Why is a 3/2WL vertical dipole on 15m a bad idea? Because the take-off-angle is high and most of the RF is lost in space. At the low of the sunspot cycle, 15m needs all the help it can get from low-angle radiation. For a vertical center-fed dipole, the length needs to be 1.25WL (or less).
Originally Posted by K9STH
73, Cecil, www.w5dxp.com
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