SSB Antenna connection

[Steve (another one)]

Dear Folks,

What is the recommended wire to connect my insulated backstay to my
AT-120 tuner ? I see references to GTO15 for this purpose in American
publications, but no-one here in the UK seems to know what GTO15 is.
Could someone please suggest an equivalent, or at least a description !

Also if the ground connection has to be broad copper strip because RF
won't run down a wire like a conventional dc current, how can the
antenna be wire ? Doesn't RF have to run along the cable to the base of
the antenna and then up the antenna wire itself ? I'm confused !

Thanks for your help.

Steve

 

[Gordon Wedman]

As has been mentioned on other posts, GTO15 is basically spark plug wire,
that is, high voltage wire. Looking at mine it seems to have a fairly thick
nylon jacket around the tinned wire core and then a thinner black plastic
outer sheath. I would think you could use high quality spark plug wire,
something with the equivalent of 16 or 22 gauge tinned wire core surrounded
by silicone insulation.
Don't know the answer to your second question.

 

[Gordon Wedman]

PS: As to the second part of your question. There have been very long

'discussions' on this group about antennas and grounds. Mostly name calling
and opinions with very few facts. I don't wish to start another one.

Well I think most of the arguments and name calling revolved around proper
methods to get an "good" RF ground.
I don't think there is much argument that you need foil for the RF ground
and something like GTO15 for the antenna connection. As to why you need 2
inch wide foil for the ground lead when circular wire works for the antenna
connection, I think that is a basic physics question that someone probably
can answer.

It is possible to get spark plug wire with wire core. Racers do not like
the carbon resistance wire and they don't care about noise on their radios.
I would agree that some extra cover over top of the spark plug wire is
probably a good idea although high quality silicone wire is pretty tough.

 

[Bruce in Alaska]

Dear Folks,

What is the recommended wire to connect my insulated backstay to my
AT-120 tuner ? I see references to GTO15 for this purpose in American
publications, but no-one here in the UK seems to know what GTO15 is.
Could someone please suggest an equivalent, or at least a description !

Also if the ground connection has to be broad copper strip because RF
won't run down a wire like a conventional dc current, how can the
antenna be wire ? Doesn't RF have to run along the cable to the base of
the antenna and then up the antenna wire itself ? I'm confused !

Thanks for your help.

Steve

Others have covered the GTO-15 question, very well.

There are a number of reasons that copper strap is used for RF Grounding
in the Maritime Radio Installations. One being, that it is desireable
for the RF Ground to have the lowest possible Impedance at the
transmitted frequency.

Two being, that it is desirable that the surface area of the RF Ground
System be as large as practicable, to maximise coupling to the seawater.

Three being, That RF flows on the surface of the conductor, and more
surface area means lower impedance on the Ground.

The antenna wire isn't supposed to couple into the seawater, but into
the ethos, so it should have the least surface area as can practically
handle the RF Current of the transmitter and be tuned to resonance by
the tuner, and as low of resistance as practicable, so that RF Current
can propagate along it's length.

Bruce in alaska Gary S. can chime in anytime on this.....

 

[Jack Painter]

Dear Folks,

What is the recommended wire to connect my insulated backstay to my
AT-120 tuner ? I see references to GTO15 for this purpose in American
publications, but no-one here in the UK seems to know what GTO15 is.
Could someone please suggest an equivalent, or at least a description !

Also if the ground connection has to be broad copper strip because RF
won't run down a wire like a conventional dc current, how can the
antenna be wire ? Doesn't RF have to run along the cable to the base of
the antenna and then up the antenna wire itself ? I'm confused !

Thanks for your help.

Steve

Steve, you have asked about two distinctly different forms of connection
that require equally different conductors. Additionally, within your
grounding questions there also are two different issues, addressed below:

1. RF feedline from ATU to antenna.

This should be coaxial cable with dialectric and shielding designed for RF.
Never improvise with something such as spark plug wires.

2.(a) Grounding: RF

This does not have to be wide surface area copper, but doing so will not
hurt, and it will allow the combination-use of the RF ground connection to
serve as a lightning protection ground. RF ground does not require a dc-
connection to ground, and is often designed to use capacitive coupling to
ground for sailing vessels and other marine applications where isolation for
galvanic protection is adviseable.

2. (b) Grounding: Lightning protection

Also does not require a dc-connection to ground, but may not use low valued
capacitors such as would be acceptable for RF ground. Lightning protection
DOES require the widest surface area possible, this provides a lower
impedance path to ground. But your radio and auto-tuner and other equipment
are most importantly bonded to each other, and that may be of any standard
braid, #8 wire, etc. Only the single connection of all your bonded equipment
to ship's ground must be of the highest surface area possible. If more than
one connection from bonded equipment to ground must be made, then each of
those connections should be wide surface area conductors.

Hope this helps,

Jack Painter
Virginia Beach, VA

 

[Steve (another one)]

NO NO NO coax from ATU to antenna, even inside a metal ship! Use GTO wire.
In an emergency repair in the Aleutians I used HV cable from a television
flyback transformer to the CRT anode once and it worked until the ship got
back to civilization. I have corrected many poor performing backstay
installations by replacing RG-8, 214, etc coax running from the ATU to the
backstay with GTO. What a difference in receive and transmit performance.

Use the widest copper foil you can find, at least 3" for the RF ground path.
The wider the better! Smaller sizes and round wire is too high impedance for
proper HF RF grounding.

Flat braid may be used is you have to use it, putting more that one flat
braid in parallel usually helps.
Doug K7ABX

Thanks for these comments, sorry if was a FAQ, I did search first. I
have since asked the same question of Icom UK and their suggestion was
to use the centre conductor of RG213u - having stripped off the outer
shielding. Someone else told me they cut back the centre conductor of
RG213u and used only the shielding which seems very odd as it would have
little insulation.

Anyway, thanks again, I think I now understand the issues and can
assemble something.

Steve

 

[Vito]

http://www.shipstore.com/ss/html/ANC/ANC150110.html

 

[Jack Painter]

RF.

Imagine what 2 meters of coax with a capacity of 200pF ( a "load" of about
200 ohms at 4 MHz) does to a high impedance (several kOhms at 4MHz) antenna
connection: right... almost short circuit it to ground.
NEVER use coax between the ATU and the antenna.

Hi Meindert, I don't understand your reasoning there, sorry. And Doug too,
who referenced a steel ship, which is my reference as well. I have seen
hardline (still 50ohm coax) in shipboard installations using the same Sunair
ATU that I use, connected to the wire HF antennas. It appears (to me) no
different that the ungrounded dipole that I feed with coax from my land
station tuners. I have also fed a longwire with that same tuner/coax
combnation, however the longwire was a grounded antenna, and not simlar to a
insulated backstay of a sailboat.

Best regards,

Jack Painter
Virginia Beach,VA

 

[Bruce in Alaska]

1. RF feedline from ATU to antenna.

This should be coaxial cable with dialectric and shielding designed for RF.
Never improvise with something such as spark plug wires.

Bzzzt, Wrong answer, would you like to try for what's behind Door No. 3??


Coaxial Cable is the WRONG Stuff to be feeding and EndFeed Longwire
Antennas with, even should you not ground the shield, which would be
disasterous in any case.
What is needed is good old GTO15, which like others have
plainly stated, High Voltage - Super High Isulation Wire. In a pinch
I have used the Center Insulation and Feedwire from RG8 or similar
coax with the shiled and jacket stripped off, but this is still not as
good as GTO15.
Yes there are a bunch of Installers who ran around using Hardline
to feed USCG MF/HF SunAirs Antenna Systems from their AutoTuners a few
years back, but the folks who had to maintain those systems 24/7 up
here in alaska, ripped all that shit out and replaced it with
conventional PhospherBronze Antenna Wire with insulators, when it was
determined that the original installations were STONED DEAF compared to
a one transistor radio.
How do I know this you ask? I was the FCC Resident Field Agent
for Southeastern Alaska, and watched it all happen.


Bruce in alaska

 

[Jack Painter]

"Jack Painter" <[email protected]> wrote:

who referenced a steel ship, which is my reference as well. I have seen
hardline (still 50ohm coax) in shipboard installations using the same Sunair
ATU that I use, connected to the wire HF antennas. It appears (to me) no
different that the ungrounded dipole that I feed with coax from my land
station tuners. I have also fed a longwire with that same tuner/coax
combnation, however the longwire was a grounded antenna, and not simlar to a
insulated backstay of a sailboat.

Coaxial Cable is the WRONG Stuff to be feeding and EndFeed Longwire
Antennas with, even should you not ground the shield, which would be
disasterous in any case.
What is needed is good old GTO15, which like others have
plainly stated, High Voltage - Super High Isulation Wire. In a pinch
I have used the Center Insulation and Feedwire from RG8 or similar
coax with the shiled and jacket stripped off, but this is still not as
good as GTO15.
Yes there are a bunch of Installers who ran around using Hardline
to feed USCG MF/HF SunAirs Antenna Systems from their AutoTuners a few
years back, but the folks who had to maintain those systems 24/7 up
here in alaska, ripped all that shit out and replaced it with
conventional PhospherBronze Antenna Wire with insulators, when it was
determined that the original installations were STONED DEAF compared to
a one transistor radio.
How do I know this you ask? I was the FCC Resident Field Agent
for Southeastern Alaska, and watched it all happen.

Bruce, I am asking why there is apparently such difference between feeding
an ungrounded dipole with coax from an ATU (my shore station) and feeding an
insulated (hence ungrounded) backstay from an ATU? I work Alaska bareback
in the summertime with that setup and I just can't understand what GTO-15
does that hardline doesn't. If you could explain or reference a document
that specifies the reasoning I would try to correct my misunderstanding.

Thanks,

Jack Painter
Virginia Beach, Va

 

[Jack Painter]

A backstay antenna is relatively short compared to the wavelength. It
therefore has a high impedance. To match it to the 50 ohm of the
transceiver, the impedance has to be transformed by an L-circuit with the
capacitance at the low impedant side to ground and the inductance from the
low impedance "hot" side to the antenna. If you would use coax at the high
impedant antenna side, you get a terrible mismatch. The capacitance of this
pice of coax adds to the L circuit at the wrong side, effectively giving you
a PI circuit which is unable to match the high impedant backstay to the 50
ohms of the transceiver.


Theoretically no. But your land dipole is probably much longer than a
backstay and therefore has a lower impedance. By the way, does your coax
connect directly to the dipole or do you have a balun (with a possible
impedance transformation wich makes the coax have less influence)?

Meindert,

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 Painter]

feeding

If I can jump in, the quick answer is that the coax is approximately the
same impedance as the center of your ungrounded dipole, at least at the
frequency for which it is resonant. Thus, from the perspective of the
transmitter and the antenna, the transmission line is "invisible." I'm
exaggerating, of course.

In the case of a backstay used as an antenna, the feedpoint impedance can be
anywhere from a small fraction of an ohm at low frequencies to thousands of
ohms where it approximates a half-wavelength. In those cases, the coax will
most certainly not be invisible and will most likely either burn up or
greatly attenuate your signal (incoming as well as outgoing, actually).

If you tried to end-feed your half-wavelength dipole with coax, you would
see a similar problem because the impedance at the ends is in the thousands
of ohms range.

Hope that helps.

Chuck, as with Meindert's answer, yes that helps, thank you.

I do end-feed a long wire as I said earlier, but it uses a 4:1 Balun, and
additionally, has one side of that Balun shorted to ground. This is a
noise-limiting design, and while the nice folks at Radio Works (Portsmouth,
Va) maintain that it cannot possibly work this way (their Baluns), the CG
aircraft I worked in Ecuador with it thought otherwise. So does it's
designer, whose name slips my mind at the moment but he was a primary
contributer to "Proceedings", and a Phd in EE with many patented antenna
designs. Anyway, it would be interesting to see some modelling done with
backstay antennas using various feedline approaches. I suspect the
difference varies greatly with wavelength, height above ground (water),
angle, and frequency.

73,
Jack Painter
Virginia Beach, Va

 

[engsol]

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

 

[Jack Painter]

<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

 

[Bruce in Alaska]

in message


Bruce, I am asking why there is apparently such difference between feeding
an ungrounded dipole with coax from an ATU (my shore station) and feeding an
insulated (hence ungrounded) backstay from an ATU? I work Alaska bareback
in the summertime with that setup and I just can't understand what GTO-15
does that hardline doesn't. If you could explain or reference a document
that specifies the reasoning I would try to correct my misunderstanding.

Thanks,

Jack Painter
Virginia Beach, Va

The fellow that followed your post did a good job in his reply.
The thing that get most of the rookie marine installers in trouble
is that they think of an antenna and tuner as if it only worked
at one frequency. They design the system for that frequency and think
they have a good system. Well it does work for one frequency but when
they try another band, things go very wrong and things just don't work
anymore. This is exactly why tuned counterpoises are an absolute JOKE
in the Marine Radio Service, but we still see them touted as the
greatest thing since canned beans. A good antenna system for a Marine
Radio Installation needs to be as efficent as possible across the whole
MF/HF Spectrum. Given a Wood or Plastic hull, this is a very daunting
challenge for the worlds best RF Engineer, let alone the SuperHam turned
Instant Expert Marine Radio Installer in a day. What is required is:
1. The Best RF Coupled Ground system one can afford to install onboard.
2. No compromise on the RF Ground System.
3. It is the RF Ground that makes the Radio work.
4. An antenna that is long enough to have a reasonable antenna
effeicency at the lowest frequency that the radio will operate at.
(this means about 75 Ft or more for 2182 Khz)
5. No compromise on the installation because of the wifes astetic
senseabilities. (build it to work, not just look good)
There are more but I think you get the idea. Just because you can
get a signal report on 12 Mhz during the day from the other coast
doesn't mean squat, about how good your Radio system is really doing.
If the band is open a 10watt TX on a dummyload can be heard on the other
coast. What makes a good system is carefully planning the installation
of the RF Ground System and then not compromising the antenna length
because you can't figure out how to install what is needed to make the
system work. All autotuners did for the industry is allow any fool to
install something that looks good, but radiates about as well as a wet
noddle. Back when all the tuners were setup by the installing Tech, he
had to actually make the system work, or he didn't get paid. Now there
is a novel thought.

Ok now I'll get off my soapbox......

Bruce in alaska

 

[Dave Morschhauser]

All --

Please comment on the following:

What about using copper tubing as an RF ground connection? Since the
current flows on the surface, a tube seems to be the most space efficient
way to get a large surface area. PI*R seems to say that a 1" copper tube
would be as effective as a 3" or so copper foil.

Any thoughts?

Thanks,
Dave.

 

[Kelton]

Did you ever try to route copper tube through all the nooks and almost
inaccessible places that you have to run the foil in a boat in order to
connect the radio, antenna tuner, and dyna-plate? I can form a coat
hanger to stick through a small crack, tape it to the foil and pull the
foil through the crack. Can you do that with copper tube. Copper tube
may give the same surface area, but installation on most boats would be
a nightmare.
Kelton
s/v Isle Escape

 

[Gordon Wedman]

The question was whether it was necessary to provide an RF ground for the

transmitter in addition to the RF ground provided at the ATU. I believe the
answer is generally no.

Well as I mentioned previously, Icom's printed literature on
antenna/transciever installation recommends grounding the transmitter to the
same ground ("boat ground") as the tuner using foil. Of course the Icom
tech that I contacted about this said not to ground the radio so everyone is
confused about this..................

 

[Bruce in Alaska]

All --

Please comment on the following:

What about using copper tubing as an RF ground connection? Since the
current flows on the surface, a tube seems to be the most space efficient
way to get a large surface area. PI*R seems to say that a 1" copper tube
would be as effective as a 3" or so copper foil.

Any thoughts?

Thanks,
Dave.

I don't know who taught you your math but 1" cooper tubing doesn't even
come close to the surface area per length of 3" copper foil. It isn't
the DC amps that you need to worry about it is the Impedance of the
connection between the RF Ground System and the Ground stud on the
Antenna Tuner. Lower impedance better Rf Ground. It is the Ground
that makes the Antenna work.

Bruce in alaska

 

[Bruce in Alaska]

Well as I mentioned previously, Icom's printed literature on
antenna/transciever installation recommends grounding the transmitter to the
same ground ("boat ground") as the tuner using foil. Of course the Icom
tech that I contacted about this said not to ground the radio so everyone is
confused about this..................

The only people who seem to be confused are those folks who don't have
much experience in MF/HF Marine Radio Antenna System installation and
design. those of us who have been doing this work for more than 30
years have had this figured out for 28 of them. I know one of the Lead
Engineers @ Icom America in Seattle, and he is a great engineer, but has
very little Field Experience in Antenna System Design. When he used to
work for SEA, he was really good at the design of the CPU's that control
the radio's, but it was the SEA Chief Engineer that had 40 years in the
design of antennas for Maritime Radio uses. Marine Antenna design is
fast becoming a Lost Art.

Bruce in alaska