Build one of those up per the published ARRL specs but don't mount it on anything - just let the assembly hang in free space, preferably from a support rope tied to the tip of the radiator section.
Next, attach feedline at recommended tap points. Then connect an antenna analyzer or GDO to the feedline and tell us where it dips...
"Everyone wants to be an AM Gangsta until it's time to start doing AM Gangsta shit."
Why good is a Garage Door Opener gonna do?Originally Posted by N8YX
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RIP ALBI-W3MIV RIP RUSS-W5RB RIP BOB-VK3ZL
Exactly. I can't build an amplifier from scratch or write microcontroller code but I'm pretty good at putting metal together in creative ways, so I'm always playing around with one sort of antenna or another. First, it was J-poles (2m, 220 MHz, 6m), more recently it's been playing with different Moxon designs (10, 15 and 20m) but I'm going to move on to Yagi-Udas and LPDAs next.
Last edited by NQ6U; 07-07-2013 at 11:11 AM.
All the world’s a stage, but obviously the play is unrehearsed and everybody is ad-libbing his lines. Maybe that’s why it’s hard to tell if we’re living in a tragedy or a farce.
Yeah, show us those skills so I can try to build an antenna worthy of the amplifier!!!
The only antennas I have had any success with have been dipoles and 1/4 wave L's with 1:1 unun, ground spike and a long radial. If i could only get the 1/4 waves to work well multiband.... I have an 80m L which works great, but is rubbish for 40m. Perhaps a trap might get it to work on 40m? I have a 40m dipole up at the moment, but that interacts with the L and makes both antennas crap.
Feeding at the centre is a bit of a pain, wires trailing all over the garden (lol theres enough of them already), need much better construction to take the extra weight etc. Been toying with the idea of a doublet with homebrew light as possible ladder line.
Last edited by mw0uzo; 07-08-2013 at 07:00 AM.
Are you using a tuner with that inverted L? Do you have an antenna analyzer?
You might try adding 20+' to the end of the "L" and see if you can match it with the tuner.
On both 80 and 40. Maybe add an extra temporary radial cut closer to 32'.
You might be pleasantly surprised. The antenna analyzer would tell you more.
Matching a half wave (40) can be a bitch.
"Where would we be without the agitators of the world to attach the electrodes
of knowledge to the nipples of ignorance?" ~ Professor "Dick" Soloman
I don't use a tuner on 80m but do when tuning other bands. I've tried adding length which just reduces performance on 80m. Antenna analyser shown dips on 3.35MHz, 11Mhz and 18Mhz. Its all a bit funny at the moment due to the 40m dipole being up. My nice 1.5-1.7 swr on 80m, 3.6Mhz has gone up to over 2 at 3.35Mhz due to this. Not sure where the other dips would be without taking it down.Are you using a tuner with that inverted L? Do you have an antenna analyzer?
You might try adding 20+' to the end of the "L" and see if you can match it with the tuner.
On both 80 and 40. Maybe add an extra temporary radial cut closer to 32'.
You might be pleasantly surprised. The antenna analyzer would tell you more.
Matching a half wave (40) can be a bitch.
As far as my limited antenna knowledge tells me, only 2 ways to get 40m on that antenna, add a trap or swap the unun for an EFHW tuner. I'm leaning towards a trap to avoid having to swap the boxes at the base of the antenna.
Other antennas that might work at my location - OCF dipole, but then 80m lost. Been considering the G4FEK antenna http://www.g7fek.co.uk/blogus/newssh...ce_anten_29507
Or as my friend suggests, a doublet taking up all the available horzontal space fed with ladder line and used with a balanced tuner.
There is approximately 20m of horizonal space available.
Once upon a time I made a number of tuners for inverted L antennas ~130' long, 1/4 wave @ 160M for loading on higher frequency bands, on 160 they were fed directly. Yeah, boat anchors with pi networks are very tolerant. SWR could be tuned to a flat match on 80, 40 and 20, beyond that adjustment got too hairy for accuracy. I have no idea what component values were, just used junk box parts and found the inductor taps by trial and error. The last one I built was breadboard, the parts found in a scrap yard were too big to fit in any available box and the thing could probably handle 50KW. SO much overkill but it would impress Doctor Frankenstein. (;->) I didn't use a counterpoise at any of my installations, yet the antenna was reasonably efficient BTW. I suppose that's because ground conductivity is reasonable in the NYC area of NJ.
"The universe is under no obligation to make sense to you."
Neil deGrasse Tyson
73 de Warren KB2VXA
Station powered by atomic energy, operator powered by natural gas.
Interesting, how does that layout differ from adding a tuner? I can tune 40m on the inverted L, but performance is terrible. Coax length is very short, just a few metres. Is it that fact that the tuner in your config is right at the base of the antenna?
EH? That layout IS a tuner and it feeds the L, counterpoise and earthing stake directly. For best results mount the whole shebang in a grounded watertight box near ground level and feed the antenna through a ceramic tit. You may also consider an arc gap and surge loop between the tuner output and antenna for lightning protection.
"The universe is under no obligation to make sense to you."
Neil deGrasse Tyson
73 de Warren KB2VXA
Station powered by atomic energy, operator powered by natural gas.
Writing fail on my part.
My question meant to ask if a short length of coax (e.g. 4 meters) between the tuning parts and the antenna affects the antenna performance.
Last edited by mw0uzo; 07-09-2013 at 06:33 PM.
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