[600MRG] The best way to transfer power from TX to loading coil

[Edward R Cole]

Wow, did I have some typos in this  (corrections/clarifications, below);

Coil is 10-inch diameter, 11-inches long, turns spaced 1/4 inch, No. 
10 house wire with insulation removed (I think that is referred as THHN?).'
End of vertical antenna is connected to a tap on the coil that uses 
about 75% of the coil length.  Other end of the coil is grounded at 
the base of the antenna.  Four radials are connected to this ground 
rod (100-foot square of land for radials).

I run approx. 100-foot RG-213 from the transmitter (NDB converted 
into a 100w linear amplifier) to a tap about 2-1/2 turns from the 
ground end on the coil; coax shield is grounded.

I think this a classic method to match an antenna that is too short.

Antenna resonance and coax match were found by experiment using a 
modified MFJ-269B antenna analyzer that tunes 400-Hz to 1200-Hz in 
the lowest freq. range.  I added inductance to the internal 
oscillator in the MFJ until it tuned the range I wanted 
(cut-n-try).  MFJ analyzer has its own freq. counter making this 
pretty simple.  Finding a small toroid of proper mix and winding No. 
26 magnet wire is most difficult part.  A trace on the MFJ pc board 
is cut and toroid is wired across which puts it in series with the 
oscillator coil for 1.8-4 MHz.  I placed a mini-toggle switch in 
parallel with the toroid to short it out to restore normal function 
in that freq range.

73, Ed

At 02:20 PM 3/17/2018, Edward R Cole wrote:
>Andy,
>
>Exactly my method:  Base coil is sandwiched between bottom 
>of  vertical wire and ground rod/radials.  Coil 10-diameter 11-inch 
>long wrapped with stripped No. 12 THHN 1/4 inch spacing per turn (45 
>turns).  Antenna connects about 3/4 of length from grounded end and 
>coax tap is about 2-1/2 turns from ground.  Maybe you suggested 
>it?  Some one from the group in 2012.
>
>Finding the antenna end tap point on the coil was done using a 
>modified MFJ-269B (added a toroid coil in series with lowest freq 
>range inductor for the internal signal generator).  Wrapped 
>wirearound the 3/8-inch toroid until oscillator worked from 800 to 
>1200 Hz.  Inserted meter between ground an coil and located the tap 
>where the complex impedance was nearly zero.  R=18 ohms at that 
>point and was used un formula to calculate ERP.
>
>May not work if you are near a BC station on lower end of BC 
>band.  Meter has no selectivity to reject BC stations signal and 
>will lead to erroneous results in finding resonance.  My nearest 
>station is 920 KHz about 15 miles away.  My inverted-L picks up BC 
>stations out thousands of miles away.  I've copied NDB's 1100 miles 
>remote from me and copied Rudy's CW FB.
>
>Not QRV but only need to tune the antenna down to 473
>
>73, Ed
>Today I shoveled snow.
>
>At 11:53 AM 3/17/2018, Andy - KU4XR via 600MRG wrote:
>>Hi all:
>>
>>I back, with a question now on the best way to transfer power from 
>>the transmitter into the loading coil..
>>I see several posts referring to auto-transformers, tappable 
>>torroid step-up / step-down transformers, etc.
>>I have a single coil, doing both jobs; TX Matching, And, Antenna 
>>Tuning .. Below is a dropbox link to a
>>picture of my Matching / Loading coil setup - to see what I am working with :
>>
>>https://www.dropbox.com/s/3b59n1djmoamm7i/KU4XR%20Matching%20-%20Loading%20Coil%203-17-18.jpg?dl=0
>>
>>The picture shows the bottom is grounded, and I tap - UP - from the 
>>bottom to match the TX for 50 ohms..
>>Is there a Better / More Efficient way to transfer the power from 
>>the TX to the Coil ? Or, is what I am doing
>>perfectly acceptable ? Any mismatch that I have is due to Unknown 
>>Reactance in the antenna that I am
>>unable to measure, and wash out at the moment..
>>
>>Thanks for comments, and suggestions, and 73 to all:
>>
>>Andy - KU4XR
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>
>73, Ed - KL7UW
>   http://www.kl7uw.com
>Dubus-NA Business mail:
>   dubususa at gmail.com
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73, Ed - KL7UW
   http://www.kl7uw.com
Dubus-NA Business mail:
   dubususa at gmail.com