Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KE0TNL, May 23, 2019.
Thanks to all for the info! That's why I ask these questions.
FWIW, I would use an Isotron or two if I was only a SWL in an impossible location---but for transmitting I'd rather operate mobile or portable with a real antenna if you know what I mean. Yeah, everything works---but an Isotron is almost at the very bottom of the list (at the bottom is a very well-shielded dummy load).
I say this not to discourage you but rather steer you in a better direction; a linear-loaded dipole could be almost half the size as a regular one and offer a lot better performance as one idea...
Good luck with your challenge and remember 10m is open more often than most of us realize due to its VHF-like characteristics.
I have a half wave wire dipole for 10 meters that I'm going to try setting up in some sort of inverted V in the opening between my balcony railing and the ceiling of the balcony above me. Experiment, experiment, experiment as they say.
Isotron Antennas, not so bad
I had one for 40 M, set it up in the back yard on a 20 ft mast and it worked OK for it's size. Was about 2 S units down Transmit and receive compared to a halfwave dipole up a few feet higher.
Not bad if you want stealth, have limited space, or for portable operation.
That is almost an understatement. The feedline is what does most of the radiation. One could do better with a length of coax with eight feet or so of wire extending from the center conductor. Look up "coaxial antenna."
This model uses a solid coaxial sleeve, but the same effect can be obtained with simply the cable itself, ideally with a choke at half-wave point on the cable. In that case , while the inner surface of the cable "feeds" the antenna, the outer surface is a radiator. Much cheaper and more efficent than an Isotron.
Sleeve Dipole is an alternate key word to search for.
I saw less of a difference than that. And some of the loss was due to the use of lossy PVC coil form material.
6 foot overall length about 15 ft up - here are the results:
Tested using reports form around the world using WSPR - https://www.qsl.net/wb5wpa/EHantenna/EH_Mark_2_Vert/
BTW - LOOK CLOSELY - this design uses link-coupling, so, no direct connection of the coax shield TO the antenna itself.
K9YC has some posted on his website; he uses about four big ferrite toroids with the coax wrapped through and around at the 1/4 wave point below the bare center conductor radiator.
Best of luck. Isotron theory sounds great but following posts say it all. My vee is feet up on home depot made mast and while I hope to save for a 4bvt better a few contacts then none.