Re: How do I best operate a 4S-Tuner with a Doublet antenna ?

Frank Perkins

Hi Bob,
Antennas are the magic part of ham radio.
Your 4sqrp tuner is a great one, basically designed for use with a "random length wire" antenna and a counterpoise wire.
For portable use, the antenna could be anywhere from 20 to 80 feet, and the counterpoise from 4 to 15 feet.
The antenna wire on the red binding post and counterpoise on the black post.
However, you are using a dipole antenna with a balanced feedline.
I would first try it connected to the red & black binding posts, and see what results you get (signal strength and direction determined by call zones received). Then switch the feedline wires and test again. Then twist both feedline wires together onto the red post and a 10 ft counterpoise wire on the black post.
Compare data. Which gave best results?
A typical dipole at about 40 ft off the ground running North and South will have the best coverage to the East and West. If only 10 to 12 feet high, it will be NVIS and work best on 40, 80, & 160, and give omnidirectional 300-500 mile range.
Later, you can build a little 1:1 and 4:1 BALUN to try between the feedline pair and the posts.
That's the fun of antennas.
I don't think you mentioned what type of rig you have, but if it's portable, take it to a park with a spool of lightweight wire.
Take a fishing pole with a 1-1/2oz sinker, sling it into a tree, pull the end of the antenna wire into the tree and have a blast!
Frank N6CES

On Tue, Apr 16, 2019, 6:58 AM Bob KM6BMX <km6bmx@...> wrote:
Hi all,

  Thanks for the replies.

  Frank, you mentioned a 4:1 balun. If I am connecting the 2-wire feedline directly to the tuner binding posts, how do I make / find a "bal-bal"? Or, are you suggesting that I use an actual 4:1 balun (2-wire feedline on one side, coax connector on the other side, and multiple turns of coax in between) and hook that to the coax antenna connector on the tuner?

  If I understand correctly, at 40m the Doublet will present roughly 50 ohms to the tuner. Since I can dial out most of the inductance and capacitance with the 3 knobs, I should be able to match with low SWR fairly quickly. 

  At harmonic shorter bands (20m, 15m, 10m), the Doublet will likely present with a higher impedance. Then, I can dial in increasing amounts of inductance and capacitance to match the antenna to the transceiver operating at the higher frequencies.

  I think that the tuner will really shine with some of other HF bands (30m, 17m, 12m). At those frequencies,  the Doublet will truly present as a "random wire".

  As you all say, I will know when I try it. Now that I have a feasible and highly portable antenna and tuner, I need to find a small HF transceiver to actually operate. Perhaps I can bring it to a Field Day or other operating event somewhere in central AZ and ask if I can try it with one of their rigs. 

  For my own rig, I am waiting until Hans Summer releases his QSX multi-mode all-HF band QRP transceiver. I Hopefully, his QRP Labs ( ) will make those available sometime this summer of 2019. 

  I am not yet CW capable and won't have time to learn Morse code anytime soon. Thus, I need a rig that supports SSB and maybe even some of the digital modes ( RTTY, PSK31, Olivia, FT-x, etc.)

Cheers & 73,
--  central AZ

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