Warning: Creating default object from empty value in /homepages/11/d132647312/htdocs/Amfone/mkportal/include/SMF/smf_out.php on line 47
LINK COUPLED BALANCED ANTENNA TUNNER USING TANDEM ROLLERS




 
The AM Forum
September 20, 2017, 07:01:26 AM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: LINK COUPLED BALANCED ANTENNA TUNNER USING TANDEM ROLLERS  (Read 350 times)
0 Members and 1 Guest are viewing this topic.
WA6PBJ
Member

Offline Offline

Posts: 4


« on: August 21, 2017, 08:33:09 PM »

Hi Forum

Can anyone connect me with someone else's construction of a LINK COUPLED BALANCED ANTENNA TUNER that USES ROLLERS IN TANDEM?? I am not speaking about couplers using baluns!! Rather the unit would use a FLOATING secondary inductor, possibly a combo of an air inductor in series with a roller..and somehow include an air inductor as the primary coupler to the secondary air inductors.  Kinda hard to explain. I guess basically it might be simply a roller in series with an air inductor and this on EACH SIDE of the link. POINT BEING: I want a unit that rids the need to TAP the ladder line onto the floating air inductor. Anyhoo...wonder if any of this makes sense.

Best 73's
WA6PBJ
Logged
N1BCG
Member

Offline Offline

Posts: 342


« Reply #1 on: August 21, 2017, 09:42:28 PM »

I tried that a few years ago and it seemed to work. The link was basically an air wound balun to convert the coax feed from the transmitter to 50Z balanced. Each lead of that connected to one end of a roller inductor and the two shafts were joined by an insulated coupler.  The rollers would then turn together, adding or subtracting the same inductance to each side. The tuning cap went across the other end of the roller inductors where the antenna also attached. Interestingly, the inductors could be uncoupled to allow balancing the currents in each feedline leg more precisely using RF ammeters.

I believe some high-end tuners work this way, purposely positioning the balun at the low impedance part of the circuit and using the matching circuitry to prevent excessive voltages at the balun.
Logged
w8khk
Marietta Georgia
Member

Offline Offline

Posts: 740


You never heard of a Ham Operator?


WWW
« Reply #2 on: August 21, 2017, 11:52:21 PM »

It's rather late, so I hope this makes sense.....

Your query reminds me of a tuner developed by W2KF, Ken Miller (SK) back in the 60s.  He used two rotary inductors, and two variable capacitors.  Preferably linked so that the capacitors and inductors had the same value when tuning.  He connected the inductors and capacitors alternately in a bridge configuration, feeding the coax from the transmitter to the top and bottom terminals of the bridge, and the open wire to the left and right terminals.  I hope this description allows you to visualize the circuit.  It worked very well, with no balun, and no link, on 75, 40, and 20 meters.  No balun, but unbalanced input and balanced output.  No switches, just one capacitor and one inductor control to adjust.

To address your goal, I visualize a link coupling over the first few FIXED turns of the output inductor, in series with the variable rotary inductors ganged with an insulated coupler.  In this manner, you eliminate the balun, and have a standard link-coupled tuner, without the need to alter taps manually.

The rotary inductors will effectively allow you to tap down the output to match the impedance of the feedline.  The split-stator capacitor, or possibly a vacuum capacitor, is in parallel with the feedline, moving to the tapped location with the rotary inductor, or, alternatively, it is connected to the far end of each rotary inductor, independent of the rotary tap location of the feedline.

I thought another interesting option of this approach might be to use two separate capacitors, one inparallel with the feedline, connected to the rotary inductor tap position, and a separate capacitor connected to the far end of each rotary inductor.  In this manner, either, or both, capacitors could be used to achieve a match.  Without any switching, either capacitor could be set at minimum capacity to render it effectively removed from the circuit.

Perhaps some software modeling, or breadboard testing of this approach with an antenna analyzer and various resistive and reactive loads could be used to validate the functionality prior to constructing the final tuner.

It seems to me that elimination of the balun and switching is a beneficial goal, and your idea deserves serious evaluation and experimentation.  It has always been a drawback to manually adjust taps on the traditional link-coupled tuner.
Logged

Rick / W8KHK  ex WB2HKX, WB4GNR
Global Warming? Actually, it's much worse! On any given day, half the planet faces global warming whereas the other half faces global cooling! The warming half is facing the sun, and the cooling half is opposite the sun
K3ZS
Member

Offline Offline

Posts: 1028



« Reply #3 on: August 22, 2017, 08:37:27 AM »

I think MFJ makes a balanced L using two rotary inductors and no baling.
Logged
K3ZS
Member

Offline Offline

Posts: 1028



« Reply #4 on: August 22, 2017, 08:38:52 AM »

Balun, damn iPad spelling corrector.
Logged
K3ZS
Member

Offline Offline

Posts: 1028



« Reply #5 on: August 22, 2017, 08:53:38 AM »

MFJ976 is what I was thinking of.  It is a dual T type.  A balun on the input.
Logged
W2NBC
Contributing
Member
*
Offline Offline

Posts: 276



« Reply #6 on: August 22, 2017, 09:05:37 AM »

This link explains the balanced double L and is a good place to start:

http://www.somis.org/bbat.html

Another:

http://amfone.net/Amforum/index.php?topic=29563.0
Logged

Vintage Radio Pages- http://www.dealamerica.com
Bob W8LXJ
Member

Offline Offline

Posts: 1


« Reply #7 on: August 22, 2017, 09:14:43 AM »

TMC Antenna Tuner  TAC-1.   2 to 30MHZ   Will tune 1.8 mhz with ease, handle 1kw AM with no problems. I use it to match a 330ft .center fed zepp, 600 ohm open wire feed, 55 ft high.  Have had it for 25 years, it is big, bulky, and very few made. Made by TMC for military use on open wire feed line antennas.

Bob W8LXJ
KW-1  #2
160, 80, and 40 meter AM
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.069 seconds with 18 queries.