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91
Antennas / Re: Magnetic antenna query
Last post by w4lix - December 04, 2020, 10:21:53 PM
For Gil. I watched your video on operation of your mag loop with the toroid feed configuration. i noticed the problem you had with matching.

i wanted to pass to you, that i use a coupling coil one fifth the diameter of the large coil
and have not had a matching problem on my operating freqs.

my present loop has a 5ft diameter made from 19 ft 3/8 od, flexable copper tubing.
so using pi, we figure
19x3.14=59.69 inches(diameter)

59.69 x .2 (1/5th) = 11.93 inch diameter (coupling loop diameter)

11.63 x 3.14 = 37.50 (length of tubing, coax needed for coupling loop)

in a nut shell, you can figure the diameter of loop to use in space you have, then you can divide your diameter by 3.14 and get length of material needed to complete loop.

my config: using two 3.5 KV air variables. both in the 40-400pfds. i have them in parallel
which allows me to use 75m to 40m bands. i run 100watts to the loop. but the efficiency is 2%
on 75-80m band, about 25% on 40m. as freqs increase, efficiency can reach 90% on 20 meters.

this info from loop design software.
i am still evaulating the loop to verticals and dipoles. off the top, i am leaning toward those antennas, then the propagation favors me, and i am suprised at my sig reports.
on a 3ft loop on 40 meters, got a report of 20db over 9! wow.

software i am using is
small magnetic loop antenna calculator ver 1.22a
by steve yates  AA5TB
aa5tb@yahoo.com


92
General Discussion / QRP-Labs QCX Mini For Sale
Last post by bkmoore - December 03, 2020, 11:54:19 PM
The QRP-Labs QCX Mini is now available here: https://www.qrp-labs.com/qcxmini.html

I wasn't originally planning on getting one, since I already have two QCXs (80m and 40m). But it is such a cute, useful and inexpensive little radio, I wound up ordering one on 20m.
93
Antennas / Re: EFHW sloper array?
Last post by N0AJS - November 10, 2020, 10:37:56 PM
Lamewolf,
 ive noticed that every time I setup my EFHWs they tend to favor the obtuse angle.   So if im "aiming" for a certain direction i tend to follow this rule. I have been very successful when i set up on the bank of a large pond or lake getting more radiation off the acute side. Water makes for a good ground plane and will help reflect the unusually low takeoff angles present on the backside of a sloper.
94
Antennas / FT-82-43 EFHW
Last post by N0AJS - November 07, 2020, 12:55:11 AM
Taking Gil's idea for using an 82 toroid I built this 64:1 transformer. Although the 3D printed box is a much more efficient use of space, I don't currently own a printer. I did find that a Hammond 1551HBK is about as good as it gets as far as size and ruggedness. The overall dimensions are 60x35x20mm. This does not have a ground connection but i have found that a small coil in my coax generally takes care of any RF on the shielding.  You cannot see attachments on this board.
95
Antennas / Re: EFHW sloper array?
Last post by Lamewolf - November 02, 2020, 09:35:21 AM
I used an EFHW sloper on 60 meters using a 49:1 transformer at the feed point that was at 7' and the far end of the wire (88') was 70' high in a tree.  Radiation was somewhat directional toward the feed point which was pointed toward the west.  But it did give good all around coverage too and had a flat swr of about 1.2:1 on all 5 channels.
96
Antennas / Re: Easy to Make Doublet for Q...
Last post by Lamewolf - November 02, 2020, 09:31:45 AM
I made a similar antenna for portable operation but I made my elements 44' long for a total doublet length of 88' and fed it with lightweight 300 ohm TV twinlead and my little homebrew Zmatch tuner for 10 thru 80 meter coverage.  The wire elements on mine was made from insulated #20 speaker wire.
97
Antennas / Re: End fed windom
Last post by Lamewolf - November 02, 2020, 09:21:14 AM
I built a Windom, but I prefer the term "Off Center Fed Dipole" and I have no issues with RF because I also incorporated a good CMC choke in the same box with the 4:1 balun - works super good !  Initial resonance is set to 3.450 mhz to get 40, 20, 17, 12, 10, and 6 meters as close as possible, then I use a capacitor with a bleeder resistor across it for protection to move 80 meter resonance up the band without effecting the other bands.
98
Antennas / Re: Balanced Line Linked Dipol...
Last post by Lamewolf - November 02, 2020, 09:12:53 AM
If you are feeding a dipole with ladder line, skip the links and just make it a half wave on the lowest band of interest and use a 1:1 current balun at the end of the ladder line with a short coax jumper to the tuner.  An 80 meter dipole fed with ladder line this way will work 10 thru 80 meters and is a very efficient antenna !
99
Antennas / Re: S8 noise at the QTH, need ...
Last post by Lamewolf - November 02, 2020, 09:04:36 AM
Don't use an AM broadcast radio as electrical nose can travel several hundred miles at those frequencies.  Instead use a scanner set to the aircraft band 116 to 136 mhz AM where the noise only travels a few miles.  Or if you have a portable rig such as the Yaesu FT-817 that will do  2 meter AM, use that.  A 2 meter, 3 element beam can be used and bought commercially or easily built.  Even a simple dipole made from stiff wire such a coat hanger wire.  You could even make a quick and easy 2 meter, 2 element beam with coat hanger wire and use a piece of 1 x 2 inch wood for the boom.

100
Antennas / Re: EFHW observations and radi...
Last post by Lamewolf - November 02, 2020, 08:40:08 AM
Stations only 50 miles away require NVIS propagation many times, so deploy your EFHW low to and horizontal to the ground, or as an inverted V with the center of the wire about 20 feet high and the ends about 3 feet high.
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