On Fri, 28 May 2004 18:58:25 -0400, "Jack Painter" wrote:


good stuff by Meindert snipped

Thanks very much, that was a lightbulb going off (duh) that the backstay on
less than a 70' yacht is going to have a seriously short antenna WRT
wavelength! My wires and dipole are of course half wave devices and at
desired frequencies do not even require a tuner at all. And yes I do use a
1:1 Balun (isolation only on the tunes dipole, 4:1 on random wires). And
just because the specs of my Sunair Coupler _could_ deal with any wire 30'
or longer, that would be a frivolous effort to try to tune, say 2182khz on
so short a wire with 50ohm coax. It does work mediocre on an 80' wire but I
am still somewhat surprised that any sailing vessel could get much
performance (if any do) on MF from a (relatively short) backstay antenna.
Closer to the 1/2 wavelength, I would think that coax would be more
appropriate to the ATU-to-Antenna match than this GTO-15. Correct? And a 4:1
balun would in other cases make the match even more feasable, as well as the
desirable electrical isolation from noise that a Balun can provide.

73

Jack Painter
Virginia Beach, Va


Jack, I too wonder about the matching of (short) backstay HF antennas.
The thing that occurs to me is that trying to match the ATU to the antenna
isn't really the goal. The ATU *IS* the matching network. By feeding the
backstay with a coax, the excess capacitance (due to the coax) is just
another reactance the ATU must try to "tune out". Using coax is equivalent
to conncting shunt capacitors from there to ground.
My opinion is that the lead, whatever it is, between the ATU and the
*real* antenna, becomes part of the antenna. To me it makes sense
to use something like GTO-15 between the ATU and backstay.
We also must remember that matching the ATU to the backstay is only
part of the job. The ATU must present a proper impedance to
the transceiver. If the antenna is a horrible match, and the ATU
runs out of "range", then the impedance presented to the transceiver must
suffer also.
Be nice to put a network analyzer on a backstay and see what it
really looks like, eh? Be an opportunity to experiment with
different grounding schemes also. I'm convinced that salt water
is the best possible ground....coupling/connecting to it is the challange.
My 2-bits worth...
Norm B

"engsol" wrote in message
...
On Fri, 28 May 2004 18:58:25 -0400, "Jack Painter"
wrote:

good stuff by Meindert snipped

Jack, I too wonder about the matching of (short) backstay HF antennas.
The thing that occurs to me is that trying to match the ATU to the antenna
isn't really the goal. The ATU *IS* the matching network. By feeding the
backstay with a coax, the excess capacitance (due to the coax) is just
another reactance the ATU must try to "tune out". Using coax is equivalent
to conncting shunt capacitors from there to ground.
My opinion is that the lead, whatever it is, between the ATU and the
*real* antenna, becomes part of the antenna. To me it makes sense
to use something like GTO-15 between the ATU and backstay.
We also must remember that matching the ATU to the backstay is only
part of the job. The ATU must present a proper impedance to
the transceiver. If the antenna is a horrible match, and the ATU
runs out of "range", then the impedance presented to the transceiver must
suffer also.
Be nice to put a network analyzer on a backstay and see what it
really looks like, eh? Be an opportunity to experiment with
different grounding schemes also. I'm convinced that salt water
is the best possible ground....coupling/connecting to it is the challange.
My 2-bits worth...
Norm B

Hi Norm, I'm still learning to use EZNEC http://www.eznec.com/ modelling
software, but I will ask a friend who works with it often to run some
typical backstay offerings and see how it portrays various configurations.

Best,
Jack Painter
Virginia Beach, Va

"engsol" wrote in message
...
On Fri, 28 May 2004 18:58:25 -0400, "Jack Painter"
wrote:


good stuff by Meindert snipped

:-)

Jack, I too wonder about the matching of (short) backstay HF antennas.
The thing that occurs to me is that trying to match the ATU to the antenna
isn't really the goal. The ATU *IS* the matching network. By feeding the
backstay with a coax, the excess capacitance (due to the coax) is just
another reactance the ATU must try to "tune out". Using coax is equivalent
to conncting shunt capacitors from there to ground.

Precisely

My opinion is that the lead, whatever it is, between the ATU and the
*real* antenna, becomes part of the antenna.

Indeed, it will radiate as much as the antenna does. Therefore it is best to
place the ATU immediately at the feed point of the backstay. The best
practical place would be directly below deck, underneath the backstay. Every
effort to keep the GTO15 as short as possible is best.

Meindert

"Meindert Sprang" wrote in
:


Indeed, it will radiate as much as the antenna does. Therefore it is
best to place the ATU immediately at the feed point of the backstay.
The best practical place would be directly below deck, underneath the
backstay. Every effort to keep the GTO15 as short as possible is best.

Meindert

Where'd this "high voltage neon wire" nonsense come from? The tiny wire
inside there is way too small for when the 50' backstay nears 1/4
wavelength at 5 Mhz where its impedance will be REALLY LOW and its antenna
current at 150 watts will be REALLY HIGH.....SAY 15 OHMS and THREE amps!
There are many frequencies at which the impedance of any sailboat backstay
antenna is LOW, not high! around 5-6 Mhz, around 15-16 Mhz where it
becomes 3/4 wavelength resonant.

I don't like this thin high voltage wire idea. Lionheart has a 8" piece of
#10 copperweld antenna wire connecting her AT-150 tuner to the base of the
backstay. This makes 40 meters just work fantastic with a good ground on 7
Mhz where the antenna's complex impedance is still very low.

73, Larry W4CSC

Sigs 5/8 to 9 in Moldova, Moscow, Czech Republic, Brazil on 7 and 14 Mhz
ham bands. Great fun working DX from Florida from the backstay.

The central conductor of GTO15 isn;t all that thin. Seems to work
well and also seems to be the standard fopr the purpose. I'm
not sure what neon wire looks like.

Doug, k3qt
s/v Callista

"Larry W4CSC" wrote in message
...
"Meindert Sprang" wrote in
:


Indeed, it will radiate as much as the antenna does. Therefore it is
best to place the ATU immediately at the feed point of the backstay.
The best practical place would be directly below deck, underneath the
backstay. Every effort to keep the GTO15 as short as possible is best.

Meindert

Where'd this "high voltage neon wire" nonsense come from? The tiny wire
inside there is way too small for when the 50' backstay nears 1/4
wavelength at 5 Mhz where its impedance will be REALLY LOW and its antenna
current at 150 watts will be REALLY HIGH.....SAY 15 OHMS and THREE amps!
There are many frequencies at which the impedance of any sailboat backstay
antenna is LOW, not high! around 5-6 Mhz, around 15-16 Mhz where it
becomes 3/4 wavelength resonant.

I don't like this thin high voltage wire idea. Lionheart has a 8" piece
of
#10 copperweld antenna wire connecting her AT-150 tuner to the base of the
backstay. This makes 40 meters just work fantastic with a good ground on
7
Mhz where the antenna's complex impedance is still very low.

73, Larry W4CSC

Sigs 5/8 to 9 in Moldova, Moscow, Czech Republic, Brazil on 7 and 14 Mhz
ham bands. Great fun working DX from Florida from the backstay.