basically a trip to home depot got me a 4" diameter PVC pipe and some aluminum flashing. used ratchet straps to secure the flashing around the pipe to bolt it all on. i did a coil inductor 1/3 of the way up the antenna in a space between the flashing, and i left a cpl feet for transmitter/feedline mounting below the antenna. for the loading coil i took a smaller PVC pipe with taps at every turn, attached the sheild to the bottom of it, and center to the roachclip for quick and precise tuning and run a 120pf arco trimmer from top of that to ground. now i did this test with no earth, heater, or electrical ground outside of what the small piece of coax sheild presented. i got a 1:1.3 match on center, and a 1:1.5 swr 10khz to either side, and 2:1 20khz after that, according to my $65 chinese ant. analyzer.
now, to see how well it radiates.
Pictures Please?
You've got my interest
Bruce.
Yes , pictures please
Barry of BBR World Wide
i will upon doing more testing. getting rained out in a minute here, and i gotta bolt the tuning coil pipe onto the main pipe better
... i might have solved the Q problem with a near-center loaded ant. ...
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Is that "Q problem" the result of a higher system Q, or a lower system Q compared to base-loading and resonating a ground-mounted, ~3-meter, Part 15 AM vertical monopole (other things equal)?
E-H antenna
its not quite an EH. its setup like a standard centerloaded vertical with a transmatch and cap to fine tune at the bottom. the Q problem we most often face comes with reduced fidelity from the sidebands getting chopped with a lot of shortened verts. even without an earth or pipe ground, i got a good SWR curve which is as i understand it, the worst case scenario. after reading about centerloaded being superior in signal but inferior in fidelity, a 4" diameter wide radiator seems like the only way to do it
Not to hijack this thread, but here is a link to a lot of info on experiments made with Electrically Short Antennas (ESA's), including the E-H. http://www.m0rzf.co.uk/EEF/index.html
Thank you for reminding me of a trannsmatch. I often wondered why you couldn't use those antenna matchers to actually tune in your AM transmitter. I remember Radio Shack used to sell an SWR matcher that went from 1 megahertz to 30 megahertz. I often wondered what would happen if I connected one of those between my AM transmitter and the antenna. Probably could use it on the talking house with the F connector and then just simply change or use an adapter to go from the F connector to a pl-259 connector. Then to the antenna matcher then to the antenna. But you would have to have an SWR meter between the transmitter and the antenna matcher. I remember two dials on that antenna matcher and you would simply tune 1 then the next one the first one you would turn to try to get the lowest SWR and then you would turn the second one and go back and forth for the best results. So if you could find a watt meter with an SWR meter that went from 1 megahertz to 30 megahertz you would be rocking out pretty good.
now sense the tram antenna for CB is helical I think it could do quite well with an antenna matcher. I remember how good those antennas work and they are around three meters. So with that being said you would have a pretty good ready-made antenna that all you have to do is use an antenna matcher with it.
my chinese sweatshop antenna analyzer says its 43ohms and 1:1.3 SWR at center, fairly consistent between 1500-1680 depending on where the cap is set on one of the taps. im fairly sure the certified transmitters running with a choked off ground work on the same principle, only with torroidals instead of the pvc,wire, and roachclip taps.
... sounds like he built an E-H antenna
The theory that a transmit antenna system can generate an E field separately from an H field has been thoroughly disproven -- per the original equations of James Clerk Maxwell, and practical experience to date with configurations claimed, or believed to be E-H antennas.