I've used parallel fed "fan" dipoles for years.
But I've never bothered with legs for 15m..
Always used the 40 m legs for 15m.. Guess a habit back
from my novice days.. Back then, my old transmitters
would match either load no sweat.. No tuner required..
Heck, I didn't even use an SWR meter when I first
started.. :/ Never missed it either..
With my modern rigs, the match on 15m, using the
40m legs is usually a tad higher than I'd like for
S/S finals..
So I slap a tuner into the picture as a "line
flattener". Even a cheapy MFJ random wire tuner will
match that.. And most internal radio tuners could
probably handle it ok.
It's not too far off from being a 3/4 wave on 15m.
None of my radios have internal tuners, but
I have several stand alone tuners.

Thank you for the response, folks. I appreciate it.

.........and OUCH!!!.......

The swr is higher than I had hoped for. I was hoping to use a duo-
band 15/40 meter wire dipole that could be fed directly with 50 ohm
coax connected to my Yaesu FT-450AT with internal tuner.

But the FT 450 AT internal tuner will only match up to a 3:1 swr, so
that won't be "do-able".

Thank you again......

FjLee KA0FPJ
Denver CO

On Apr 7, 7:00*am, " wrote:
Thank you for the response, folks. *I appreciate it.

........and *OUCH!!!.......

The swr is higher than I had hoped for. *I was hoping *to use *a duo-
band *15/40 meter wire dipole *that could be fed directly with 50 ohm
coax connected to my Yaesu FT-450AT with internal tuner.

But the FT 450 AT *internal tuner will only match up to a 3:1 swr, so
that won't be "do-able".

Thank you again......

FjLee * * * * KA0FPJ
Denver CO

See QST Dec. 1991 Hints and Kinks. The author cut the dipole for the
low end of 40M~67' and used a Q section of RG59 cut for 21 MHZ to
improve the match on 15M.

Gary N4AST

wrote:
Thank you for the response, folks. I appreciate it.

........and OUCH!!!.......

The swr is higher than I had hoped for. I was hoping to use a duo-
band 15/40 meter wire dipole that could be fed directly with 50 ohm
coax connected to my Yaesu FT-450AT with internal tuner.

But the FT 450 AT internal tuner will only match up to a 3:1 swr, so
that won't be "do-able".

Thank you again......

FjLee KA0FPJ
Denver CO


I think it *will* work (based on practical experience.. I've done this a
bunch of times).. you just need to fiddle with the length to get an
acceptable match in both bands. And, of course, you're not going to get
something which matches the bottom of one band and the top of the other.

People fling up dipoles (theoretical feedpoint Z around 70 ohms) and
feed them with 50 ohm coax all the time and never give it a second
thought. (partly that's because rarely is the dipole perfectly flat..
if it droops or peaks up, the Z gets closer to 50 ohms)

The swr is higher than I had hoped for. I was hoping to use a duo-
band 15/40 meter wire dipole that could be fed directly with 50 ohm
coax connected to my Yaesu FT-450AT with internal tuner.

But the FT 450 AT internal tuner will only match up to a 3:1 swr, so
that won't be "do-able".

I think it *will* work (based on practical experience.. I've done this a
bunch of times).. you just need to fiddle with the length to get an
acceptable match in both bands. And, of course, you're not going to get
something which matches the bottom of one band and the top of the other.

I agree, it may very well work acceptably. I've been able to get a
similar 40-meter wire to match up OK on 15 meters, using the autotuner
built into my Kenwood TS-2000.

Another option would be to add some sort of matching element, either
at the antenna or at the rig, which would bring the feedpoint
impedances on both bands to within the ranges acceptable to the rig's
internal tuner.

If the antenna is close to 50 ohms resistive in the 40-meter band, and
is around 85.26 - J 186.3 in the 15-meter band, then you could
consider adding a series coil at the antenna feedpoint. If I'm doing
the numbers right, an inductance of 1.5 mH at the feedpoint would
cancel out the 186 ohm capacitive reactance almost exactly, leaving
you with an 85-ohm resistive impedance or an SWR of around 1.7:1, which
should be quite easy to drive.

This much inductance would change the feedpoint Z on 40 meters to
around 50 + J60, so the SWR would be quite a bit more than 1:1...
probably still within the range of your tuner, though.

Several ways to deal with this:

- Compromise, by using less series inductance... maybe 1 uH - this
wouldn't lower the SWR on 15 meters as much, but would raise the
SWR on 40 meters less. Calculate and fiddle a bit and you can
probably find an inductance which will result in similar (and very
comfortable) tuning SWRs on both bands.

- Instead of a plain L at the feedpoint, use a series LC - one which
is series-resonant at 40 meters (thus adding no reactance and not
changing the SWR at all) and has a net reactance of J186 at 15
meters.

All of these techniques will narrow the SWR bandwidth on 40 meters
somewhat, but with care you should end up with an easily-tunable
antenna.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

In article ,
Dave Platt wrote:

If the antenna is close to 50 ohms resistive in the 40-meter band, and
is around 85.26 - J 186.3 in the 15-meter band, then you could
consider adding a series coil at the antenna feedpoint. If I'm doing
the numbers right, an inductance of 1.5 mH at the feedpoint would
cancel out the 186 ohm capacitive reactance almost exactly, leaving
you with an 85-ohm resistive impedance or an SWR of around 1.7:1, which
should be quite easy to drive.

.... for which, please read "1.5 uH" - micro rather than milli :-(

Similar errors elsewhere in my posting.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

On 04/07/2011 10:47 AM, Gary wrote:
On Apr 7, 7:00 am, wrote:
Thank you for the response, folks. I appreciate it.

........and OUCH!!!.......

The swr is higher than I had hoped for. I was hoping to use a duo-
band 15/40 meter wire dipole that could be fed directly with 50 ohm
coax connected to my Yaesu FT-450AT with internal tuner.

But the FT 450 AT internal tuner will only match up to a 3:1 swr, so
that won't be "do-able".

Thank you again......

FjLee KA0FPJ
Denver CO

See QST Dec. 1991 Hints and Kinks. The author cut the dipole for the
low end of 40M~67' and used a Q section of RG59 cut for 21 MHZ to
improve the match on 15M.

Gary N4AST

A very simple solution in:

http://www.astrosurf.com/luxorion/qsl-g5rv-2.htm

Near the end, look for:

How to tune a 40-meter dipole antenna on 15 meters ?


Alejandro Lieber LU1FCR
Rosario Argentina

Real-Time F2-Layer Critical Frequency Map foF2:
http://1fcr.com.ar

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