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Messages - Lamewolf

#16
Antennas / Re: Trapped EFHW info
June 21, 2017, 08:53:38 AM
I already posted a diagram of the 64:1 transformer in a thread here: http://radiopreppers.com/index.php/topic,1292.0.html  in case you want to build one.
#17
Antennas / Re: Trapped EFHW info
June 21, 2017, 08:50:17 AM
Quote from: caulktel on June 11, 2017, 06:58:42 PM
Hi all,

I normally use EFHW antennas for all my portable ops with a 28ft fiberglass pole, but they are all mono band, so I got this idea to make a multi band 20,40 meter EFHW using these traps from, http://www.sotabeams.co.uk/pico-traps-kit-pair/ I understand how to tune the traps, but I'm not clear on how to determine where to place the trap on the wire. I assume being as I want to use it on 20 and 40, that it needs to be approximately 66 feet long total length, but where do I insert the 20 meter trap, at 33 feet? I have done a lot of searching, but have not found a definitive answer on how to figure it. Do I build the 20 meter section first with the trap at the end and tune it to length, then add the 40 meter section? Any help would be appreciated.

Joel
N6ALT

Use a 64:1 transformer to feed an end fed half wave for 40 meters and it will work 20 an 15 meter also without a tuner and without traps !
#18
Antennas / Re: End fed half wave for 60 meters
May 30, 2017, 08:49:37 AM
Quote from: gil on May 28, 2017, 04:59:48 AM
Thank you. I wish we had 60m here in France...

Gil.

That device will also work with end fed half waves for other bands !
#19
Antennas / Re: The SotaBeams Valley Tuner on 80m.
May 27, 2017, 01:12:56 PM
The MFJ-16010 will do it too !
#20
Antennas / End fed half wave for 60 meters
May 27, 2017, 08:58:47 AM
Been experimenting again with end fed half waves and methods of matching them.  Build a broadband matching transformer to use with my EFHW 60 meter antenna and its working great !  Its flat on 60 meters and close enough (2.5:1) to use with my built in ATU in my FT-450AT on 30 meters and 15 meters.  Thought I would share a diagram on the transformer.
#21
Here is a better detailed diagram of what I built.

#22
I had added it to the other thread about the modified OCFD but wasn't sure anyone had seen it, so put it under a new thread to make sure.
#23
Just thought I would share a couple of diagrams with the group on my modified off center fed dipole that is working great so far.  The modification is the addition of a 120pf 5KV capacitor to move the 80 meter resonance more toward the center of the band without effecting the upper bands.  The cap also has a 1 megohm 5 watt carbon resistor across it to protect it from static damage.  The diagrams also have swr readings for my particular antenna - ENJOY !
#24
Finally got this thing working and here is the results in diagram form.

#25
Antennas / Re: Coax Length and SWR.
April 01, 2017, 09:50:29 AM
If you want a true swr reading on your antenna, then use an "ELECTRICAL HALF WAVE LENGTH" of coax which duplicates at the shack end what the impedance is at the load end.  By "electrical half wave" I mean a coax that is cut to length by factoring in the velocity factor of the given coax.  So if the velocity factor is 66%, you would do the math of 468/Freq in MHz = length in feet X .66 or 468/3.5 = 133.71 X .66 = 88.25 feet.  Once you get the antenna resonant at 3.5 MHz with that length of coax, it shouldn't matter what length of coax you use because it will be looking into a purely resistive load.  The reason different lengths of coax effect swr is because its not a purely resistive load and is effected by reactance.  Doing it this way is pretty much splitting hairs but it is more accurate !
#26
Antennas / Re: Super Gain 9db 40m NVIS Antenna.
March 24, 2017, 08:46:44 AM
Quote from: Quietguy on March 23, 2017, 09:11:28 PM
Quote from: DJ6KR on March 23, 2017, 10:00:54 AM
It is all about the reflector on the ground under the Antenna, I think.

Yes, I have a copy of Terman's book that is referenced in the article.  Terman discusses a "Half-wave Antenna with Reflector" starting on page 903 and derives the gain.  He shows plots of gain compared to radiation resistance as a function of antenna to reflector spacing.  Radiation resistance (and efficiency) goes way down with small spacing, while gain stays around 8 up to a spacing of about 0.1 wavelength (about 13 feet on 40 m) before falling off with increased spacing.  He says:

"In order to prevent incidental loss resistances from making the antenna efficiency very low, the spacing S should accordingly be at least 0.05 wavelength, and preferably 0.1 wavelength."

The article uses 7 feet, which is about 0.05 wavelength at 40 meters, but Terman's chart shows you would have better efficiency without losing gain if you made the antenna 14 feet high.

Wally

I can see that in my minds eye, but the gain they are speaking of in this article is going straight up !  Good for NVIS, bad for DX !
#27
Antennas / Re: Super Gain 9db 40m NVIS Antenna.
March 23, 2017, 08:31:45 AM
I just don't see how they can claim that much gain when the antenna is basically nothing more than a half wave folded dipole.  The idea behind a folded dipole is increased bandwidth, not more gain ?
#28
Antennas / Re: Random Wire Antennas Can Be Troublesome.
February 27, 2017, 04:33:32 PM
Quote from: gil on February 24, 2017, 01:20:58 PM
QuoteUse an FT140-43 core and wind 18 turns of RG174 cox on it

Good one... I have slip-on ferrites that are just the right diameter for RG-174. If that doesn't work I'll try the toroid.

Gil.

It will take a bunch of slip on beads to do the same as one toroid with those 18 turns on it.  The toroid & 18 turns would be about 6000 ohms @ 80 meters !
#29
Antennas / Re: Random Wire Antennas Can Be Troublesome.
February 24, 2017, 10:15:06 AM
Gil,

Use an FT140-43 core and wind 18 turns of RG174 cox on it for a very effective 1:1 choke to install between the 9:1 and the coax and run a counterpoise wire on the antenna side of the unun.
#30
Antennas / Re: The Elecraft T1 Automatic Tuner.
January 11, 2017, 05:28:41 PM
Quote from: cockpitbob on December 21, 2016, 09:53:31 AM
That tuner has been on my list for a while :).  /jealous

I hadn't thought about protecting the finals while it finds, or fails to find a tune.  I can't turn down the power on my MTR and I run it at 12V so it's in the danger zone for a bad mismatch.  Would you worry about using this tuner with your MTR and for example a random wire with 9:1 unun?

You guys could build a simple resistive bridge that can be switched in and out of line for tuning purposes just like the one built into Gil's ZM-2 tuner.  A few resistors and a DPDT mini toggle switch, and inline (tune position) the radio has a decent load, when done tuning, just switch it out of line to operate.  If the radio has enough room, the bridge can actually be built inside it !