Ham Radio - The Doublet. An old but good multi-band single dipole antenna. Part 1

Optimal setup with the Tuner at the base of the antenna system.

 

The article , information and video is all about - what works good ! and why ?
Excellent material for beginners and coaxial guys, not to much technical, and very well explained. Well done , I am D.I.Y Ham and Love seen articles like these - for ANY HAM, this would be a step fw in the right direction. Thx guys , GB nd Gd DX 73

 

In support of the above from KR3DX, again from the DJ0IP website; the best way to transition from open wire or ladder line feed from an 80 meter half wave dipole is with a 1:1 balun in the coax at the site of transition between the two feedlines, then as short as possible run of coax to the conventional style antenna tuner. A 4:1 balun used with a non resonant antenna can be disastrous, as because of the high swr it doesn't do effective common mode current blocking or a proper impedance transformation.

Instead, use a 1:1 current balun, which you can easily make from 10 turns of the coax on a couple of stacked 2.4" type 43 material cores. This will give over 4k ohms common mode choking impedance at 3.5MHz, adequate.

Recommend a read of :
http://www.dj0ip.de/balun-stuff/baluns-for-tuners/

"DO NOT USE A 4:1 BALUN FOR THESE APPLICATIONS:

EXAMPLES:

• 80m Dipole fed with openwire and used on 40m (impedance is about 60 Ohms on 80m, but *2000+ Ohms on 40m). This is the wrong place to use a 4:1 or 6:1 balun and will result in severely degraded rejection of the common mode current. DO NOT DO THIS (and do not listen to the people who tell you it is OK). It only works OK when running very low power.

• 40m Dipole fed with openwire and used on 80m (about 10 Ohms impedance). The 4:1 balun transfers it downward to 2.5 Ohms -
• THIS IS DISASTEROUS! This is WORST CASE. Do Not Use It. Use a good 1:1 current balun for this.

*Impedance will also vary with the length of the feedline, but this is a realistic possible value."

 

I really really really really wish someone built an updated Johnson Matchbox for the WARC bands. The doublet just SCREAMS for a good link coupled tuner.

 

He was referring to using the balun or cmc choke on the input of a balanced tuner.

Putting a balun on the output side of a balanced tuner doesn't make sense. You'd need three if you did that. One would convert your balanced feedline to unbalanced, then another to connect that unbalanced connection to the output of your balanced tuner, and finally a third balun to connect the input of your balanced tuner to you unbalanced (coax) feedline from the rig.

An unbalanced tuner like most people have is a different animal.

A home brew balanced L can be made on the cheap and works as well as a store bought unit that costs hundreds. Since the balun is on the 50 ohm side of the tuner you know you'll need a 1:1.

 

Great video down to Earth with excellent instructions. I use this type of antenna on 160 meters with and wit hout the 4:1 balun directly to RG8-U coax at the basement window. I use reverse beacon to test my antennas for directional properties. Also use the various SDR receivers located coast to coast to listen to my signal. The best antenna is still the regular single band dipole or for maximum efficiency. Looking forward to your next video.

 

Great video about one of the very few non resonant multiband antennas that really performs.

A rotary aluminum dipole fed with 450 Ohm open wire, a 1:1 current balun outside of the sack and 2m or coax to wide range tuner is my all time favorite 20-6m aerial

 

My only antenna for HF currently is a doublet cut roughly for 40 meters and fed with RS 300 ohm window line and matched with an old Johnson-Viking matchbox - no balun. Admittedly, I'm no antenna guru but this antenna system seems to work quite well from 40M up to 10M. It will also tune up well on 80M but is a bit more persnickety. I realize the use of RS 300 ohm window line may draw some criticism but once again, it's working for me but I rarely run no more than 50 watts give or take, mainly because I'm conservative but what I have learned with this antenna system is that for most contacts, 50 watts and below gets the job done - and with good signal reports most days.

Say what you will about these old matchboxes...it's as big as your grandfathers Buick - the largest item sitting on my shack table - but it works quite nicely in this application and will still be here and functional when I'm not. I digress...

Great article and video. Well done!

 

No balun required on a link coupled tuner like the Johnson matchbox.

 

A link coupled tuner like the Johnson Matchbox is a balun.

 

Nope. The best antenna is one that gets you on the air !

 

I was fortunate to have Pat Buller (W7RQT SK) build a superb link coupled balanced tuner for me before he passed away.

Pat was an extremely talented RF engineer who made his tuners along the lines of the Johnson Matchbox but With more taps for better frequency agility.

I’ve used it on a 175’ long doublet fed with a true open wire feedline (made with ceramic spacers) for around 20 years.

This is the one of the best solutions for feeding and matching doublets, but unfortunately few such tuners are readily available these days.

 

I've tried different dipole/tuner combinations over the years with coax and 300-450 ohm ladder line. Switching to the 600 ohm open wire (W7FG made) and a 130' dipole is a combination I swear by. Worked great in Montana and wonderful in Belize for world wide propagation. K7YB/V31YB