Connecting built in antenna tuner to ladder line.
 

Thanks to the generosity of a fellow radio club member I now have the
use of a Yaesu FT-1000 (no Suffix). Since it has a built in antenna
tuner, that I'm hoping to use, I need to ask what the best way is to
couple the window line that feeds my folded dipole antenna into a
short; say twenty feet; coaxial feeder from the radio. I used an Icom
AH4 antenna coupler with my FT-857D on this antenna with very good
results. I would guess that I need a balun but which type is a
mystery to me.

So is a balun a good solution to this challenge or should I resort to
the two pieces of coax in parallel that I have read of elsewhere?
When you use the two parallel coax leads do you ground and/or bond the
two shields at the transceiver end? Further since the FT-1000 does
not have obvious balanced feed line terminals would I connect a
balanced feed line to the ground terminal and the the center pin of
the SO239 connector by using say a banana plug.

Since I really am asking questions I hope there is already a consensus
answer as I would not be able to sort out the various sides of any
debate. Thank you in advance to all who choose to tackle this
question.

Tom Horne W3TDH

Connecting built in antenna tuner to ladder line.
 

On Sunday, November 25, 2012 4:08:00 PM UTC-6, Tom W3TDH wrote:
Thank you in advance to all who choose to tackle this question.

Assuming your folded dipole is a resonant antenna with a feedpoint impedance around 300 ohms, with a 1:1 balun, the 50 ohm SWR would be 300/50=6:1 and that is probably outside the range of most built-in autotuners. Assuming a 300 ohm feedpoint impedance, a 4:1 balun would bring the 50 ohm SWR down to 75/50=1.5:1. 4:1 baluns are inexpensive so I suggest a 4:1 balun as a first try. You might get by with the less expensive 4:1 voltage balun but I recommend a 4:1 (dual-toroid) current balun.
--
73, Cecil, w5dxp.com

Connecting built in antenna tuner to ladder line.
 

Tom W3TDH skrev 2012-11-25 23:08:
Thanks to the generosity of a fellow radio club member I now have the
use of a Yaesu FT-1000 (no Suffix). Since it has a built in antenna
tuner, that I'm hoping to use, I need to ask what the best way is to
couple the window line that feeds my folded dipole antenna into a
short; say twenty feet; coaxial feeder from the radio. I used an Icom
AH4 antenna coupler with my FT-857D on this antenna with very good
results. I would guess that I need a balun but which type is a
mystery to me.

So is a balun a good solution to this challenge or should I resort to
the two pieces of coax in parallel that I have read of elsewhere?
When you use the two parallel coax leads do you ground and/or bond the
two shields at the transceiver end? Further since the FT-1000 does
not have obvious balanced feed line terminals would I connect a
balanced feed line to the ground terminal and the the center pin of
the SO239 connector by using say a banana plug.

Since I really am asking questions I hope there is already a consensus
answer as I would not be able to sort out the various sides of any
debate. Thank you in advance to all who choose to tackle this
question.

Tom Horne W3TDH


A 4:1 current balun, A.K.A as a 4:1 Guanella balun, does a god job.
Constructions using just 2 coax-lines will have problems to cover all HF
bands. To little inductance at the lower bands and you have to keep the
length less than a quater wave on the higher ones.

Google on 4:1 guanella balun and you will find a lot of sites that shows
how to make one. Just be aware of those who just uses one core, these
designs will degrade the performance (common mode) of the balun.

73 and Good Luck
Ben / SM0KBW

The key is to only use resonant antenna's....

IN the early days of amateur radio, there was no coaxial cable - hence we did not care much what the SWR was.
We used a Johnson Matchbox with a couple of coils and life was good.

Then after world war two - coax became available and people bought it because it was cheap and it worked.
The problem was - how to match it.

The regular MFJ 949 series tuner was usually employed - although most people do not understand that it cannot make a non resonant antenna resonant.
The bottom line is - even if they claim they can work everything they can hear - what are they hearing?
Not everything that a person with a resonant antenna hears....

Having a good transceiver to use, and not wanting to damage it - you want to buy the best possible antenna's for the money...

One point I always make with new hams and inexperienced hams is to do lot's of research and to listen before transmitting...
Listen, listen, and listen some more......

There are lot's of nets with real hams up on 80 and 160 meters - if you can find them that knows a little about this stuff...

Some good web pages to look at are K3CC, K0BG, KC9AOP

Connecting built in antenna tuner to ladder line.
 

On Wednesday, November 28, 2012 5:50:28 PM UTC-6, Channel Jumper wrote:
The regular MFJ 949 series tuner was usually employed - although most
people do not understand that it cannot make a non resonant antenna
resonant.

Apparently, some people don't understand the maximum power transfer theorem.. An antenna tuner establishes a Z0-match to 50 ohms, commonly called "making the transmitter happy". If the antenna system is a low-loss system, the effect of that Z0-match in the shack is a near-conjugate match at the antenna feedpoint which guarantees maximum transfer of available power to the antenna. It doesn't matter if the antenna by itself is resonant or not. Conjugately matched *systems* ARE resonant.

Let's assume we have a non-resonant antenna with a feedpoint impedance of 100+j200 ohms. If we feed the antenna with open-wire line and adjust the antenna tuner in the shack such that the impedance looking back down the transmission line towards the source is 100-j200 ohms, the reactance is neutralized, i.e. *system resonance* is established with an apparent 100 ohm source and 100 ohm load thus ensuring maximum transfer of available power.

The well-respected Extended Double Zepp is an example of a non-resonant antenna that will outperform a resonant 1/2WL center-fed dipole in the dipole's favored direction. Note: with the feedline disconnected, a 1/2WL center-fed dipole is non-resonant. Connecting the coaxial feedline resonates the antenna system just as connecting a properly tuned open-wire feeder resonates the antenna system.

Consider a 50 ohm 1/2WL resonant center-fed dipole fed with 1/2WL of open-wire line. The SWR on the feedline is 12:1, i.e. a severe impedance mismatch exists at the antenna feedpoint. Yet, the transmitter sees 50 ohms and this mismatched system is more efficient than most coax-fed antenna systems.
--
73, Cecil, w5dxp.com