[HCARC] Wideband 80 meter antenna

[Dale Gaudier]

FYI, the SWR I have previously reported for the broadbanded 80m antenna (2:1 or better over 420 kHz of the 80m band) was measured with the antenna center at 32 ft. hanging from a military surplus aluminum push-up mast. The ends of the antenna are at 15 feet above ground level, configured in a shallow inverted V. The antenna is fed using about 50 feet of RG-8X coax. Measurements were taken at the transceiver end of the coax using my Rig Expert AA-56 antenna analyzer. Modeling indicates the SWR will further flatten as the antenna is raised. Lengths and spacing of the elements can be adjusted to place the ranges of resonance (there are two) wherever desired in the 80m band. It will still radiate mostly straight up (NVIS) until you are near 1/2 wavelength above ground.

There are many designs and concepts for broadbanding an antenna for 80m. I have a whole collection of articles on these. Some are simple and some are complex. I don't make any claims that my design is the best - it was one I was curious to try out. The design criteria was to cover the entire 80m band with a relatively simple to construct dipole antenna that was lightweight, inexpensive, has a nominal input impedance of 50 ohms, and could be fed directly with 50 ohm coax without an impedance transformer. As a bonus, I learned how to make cheap open wire feedline, since the technique for making the broadbanded antenna elements is identical to that for making open wire feedline.


73,

Dale - K4DG


-----Original Message-----
From: hcarc-bounces at mailman.qth.net [mailto:hcarc-bounces at mailman.qth.net] On Behalf Of SARA SANDSTROM
Sent: Tuesday, February 11, 2014 10:21 AM
To: Gary and Arlene Johnson
Cc: H - Reflector
Subject: [HCARC] Wideband 80 meter antenna



Gary, 

The impedance of an antenna in a real installation is seldom what is expected.  If the antenna is well above ground and away from metal objects (free space!) , its impedance will be close to its design value .  A temporary installation for NVIS operation is going to be close to the ground, less than a quarter wave, and probably close to conducting/lossy objects.  For 80 meters, a 20 ft center support and 10 ft end supports are probably adequate.  I would put the ends up 10 ft just so animals and people don't run into them.  I think that you will almost certainly need to have an antenna tuner with you no matter what antenna you use.  I doubt that the built in auto tuners will have enough range to be useful.  For 100 W, the MFJ tuners are probably more than adequate.  

I think Bill Tynan suggested a dipole cut for 3600 kc (kHz!) and SSB operation near 3600 and CW/PSK between 3550 and 3600 is a sound idea.  By the way, we can legally operate CW in the phone bands, so we don't need to change to another frequency for CW.  I'm not sure whether PSK is legal in the phone bands, but it might also be.  Since we will only be working among ourselves and not looking for random contacts, operat ion in the traditional segments isn't required.  We just need to be sure that there is an Extra Class operator in each group so we can operate just above 3600 kc. .   

Temporary emergency operation is always unpredictable.  We need to be able to handle anything that comes up.  A simple antenna and a small lightweight tuner is insurance that we'll be able to get a reasonable signal on the air.  Choice of rig is the same thing.  We need to choose simple rugged rigs of the roughly 100 W level and simple reliable laptops for PSK. 

Kerry
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