Re: Antenna Question #antennas #v3


Jim Willis
 

Hear, hear...

Best regards,

Jim

On Mar 17, 2020, at 6:22 PM, Gordon Gibby <docvacuumtubes@...> wrote:


McRuss -- fantastic idea!!!!    I saw the 17 foot telescoping stainless steel MFJ whip at the Orlando hamfest and that looks VERY interesting, and of course the venerable HAM STICKS are also quite long.

Getting LENGTH IN THE CLEAR raises your "radiation resistance" and thus reduces your losses dramatically.  

In microwaves they speak of the "aperture" of an antenna --- the effective area of radio waves that it intercepts and whose energy it extracts to turn into femtowatts of power heading for your receiver input.   You want the largest "aperture" reasonably possible --- because antennas in generaal are RECIPROCAL.    To get a large output signal, you need to have a good sized APERTURE.    Smaller antennas are often described as "quiet".   THat makes sense --- they just don't pick up a lot of signal!!!   Larger antennas may pick up more galactic and thunderstorm static.....but they also GET OUT better!

Running a tuner to the 17 foot vertical temporarily clamped somewhere would give you some reasonable amount of metal in the sky to load into.   The incredibly high input impedance of a halfwave resonant end fed (couple thousand ohms) allows easy feeding with a simple 49:1 balun (sold commercially or put your own together with 3-4 turns, and 21-28 turns on the secondary on an FT-240-43 or FT-140-43 core) -- and an almost invisible wire can be your antenna.   Forget running coax out...just insulate the tiny wire and try to run it out a WOODEN or non-conductive slit under a window or door to the outside and outward with invisible fishing line holding it away from the building.    I've used that type of antenna very successfully from a BUS STOP to make winlink connections and do research.     Of course you can also use any standard tuner made for long wires also....use "ground" as the other terminal (I wouldn't put it past me to conect to the green wire of the power system since on a high rise, you will never get to real "ground".   )  

Allison, an RF engineer on this site has always pointed out to get the most wire you can, as far away from obstructions as you can, as high as you can....and she is giving very very wise advice.   Then, match to it, however you can!

73

Cabin-fever Gordon KX4Z



On Tue, Mar 17, 2020 at 6:02 PM McRuss via Groups.Io <wtrrtw=yahoo.com@groups.io> wrote:
As I'm confined (not quarantined) to a condo unit, I thought a mag loop would be my answer.  Maybe it was the one I bought and maybe it was defective but I could never get the SWRs down low enough to use it.  They are super sensitive to tune also.  My ..03  My answer turned out to be a 'Super Antenna' vertical, mounted on the railing of my balcony (CCR's prohibit it from "protruding from the balcony" so it does not).  I ran the two radials into two downspouts for the gutter and they are hidden and the antenna works great.  Sometime next week I hope to have my V6 up and running on said antenna!
--
Newbie
K5FJR

Join BITX20@groups.io to automatically receive all group messages.