Maker Pro
Maker Pro

use standoffs between SSB coax and backstay??

G

Gordon Wedman

Jan 1, 1970
0
The other day I was wandering around one of our marinas trying to steal
ideas from other boats and I came across an aluminum pilot-house sloop that
may have come over from Europe. I noticed that the SSB coax was held away
from the backstay turnbuckle and wire by ~1 inch plastic spacers. I've
never seen this before and the previous owner didn't do it on my boat. I've
been thinking of upgrading the ancient SSB system on my boat and was
wondering if these standoffs were something recommended.
Anyone know about these? Thanks
Gord
 
G

Glenn Ashmore

Jan 1, 1970
0
I think I read somewhere that the high voltage GTO wire should optimumly
approach the backstay at right angles. Something about when the lead
runs close and parallel to the grounded section some power is leached
off. Not real practical in most cases though. Stand offs about 1 1/2"
long keep the lead wire away from the stay enough to prevent significant
loss and are a pretty good way to keep things neat but probably not the
most electrically efficient.

OTOH, if you have this RF hot wire running up the stay where anyone can
grab it, why have a lower insulator in the first place? I am
considering not grounding the backstay chainplate and feeding the tuner
directly to one of the bolts. Just have to remember to yell "If you
have to pee off the stern rail Don't hold the backstay!" before sending
any e-mail. :)

Gordon said:
The other day I was wandering around one of our marinas trying to steal
ideas from other boats and I came across an aluminum pilot-house sloop that
may have come over from Europe. I noticed that the SSB coax was held away
from the backstay turnbuckle and wire by ~1 inch plastic spacers. I've
never seen this before and the previous owner didn't do it on my boat. I've
been thinking of upgrading the ancient SSB system on my boat and was
wondering if these standoffs were something recommended.
Anyone know about these? Thanks
Gord

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com
 
G

Glenn Ashmore

Jan 1, 1970
0
It was probably GTO-15. I would hope that who ever went to the trouble
of adding the standoffs would know the difference. GTO is hard to tell
from RG59 from a distance. Neon sign suppliers even have it in
decorator colors.

Larry said:
If the backstay turnbuckle were "hot" (energized with RF) this would
be prudent because there can be considerable voltages from the tuner
on certain frequencies, such as near when the backstay is a 1/2
wavelength antenna.

The question arises, why does the coax go to the backstay AT ALL? It
goes to the TUNER who's tuned RF output goes to the backstay. I has
no business going to the backstay.

The wire from the tuner's high voltage post to the backstay shouldn't
be coax, either. Coax has LOTS of capacitance to the shield and if
some idiot grounds it it will decouple the RF off to ground at the
higher impedances.... A heavy wire should hook the tuner to the
backstay as it's just part of the antenna.









Larry W4CSC

"Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com
 
G

Glenn Ashmore

Jan 1, 1970
0
GTO-15 is 15KV insulated wire and fairly standard for tuner to backstay
leads. More for safety than efficiency. The whole idea of elevated
lower insulator on the backstay is to prevent some dumb crew member from
grabbing a hot lead and getting an RF burn. The GTO limits that
possibility. The stainless strap approaching at an angle is probably
more efficient and neater looking but gives no protection. West Moron
dropped it from the Catalog this year but used to sell it for $1/ft. It
is standard material in neon shops for $.50/ft and from HVAC dealers as
spark igniter wire for $.25/ft.

Larry said:
What the hell is GTO-15, some West Marine $20/ft trick? This isn't a
neon sign with 40KV of 60 Hz on it....IT'S RF! All the insulation in
the world isn't going stop the RF from leaking out, like it's 'spozed
ta. Lionheart's tuner is hooked to its backstay with a stainless
strap in a gentle curve held on with a stainless hose clamp.

Now that we got the damned steel cable holdin' the boom up replaced
with something that DOESN'T suck off the HF signal into the mainmast,
it works much better......well, at least until the sun exploded wiping
out the ionosphere....

73 DE W4CSC

NNNN

AR

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com
 
G

Gordon Wedman

Jan 1, 1970
0
Thanks to all for the discussion. For the minimal effort and expense it
sounds like a good way to save a bit of transmit power.
Sorry about the reference to "coax". As I'm not very knowledgeable about
these things I couldn't really state what type of wire it was and just
guessed coax. Thanks for pointing out the correct wire to use. I don't
think my boat currently has this.
 
B

Bruce in Alaska

Jan 1, 1970
0
What the hell is GTO-15, some West Marine $20/ft trick? This isn't a
neon sign with 40KV of 60 Hz on it....IT'S RF! All the insulation in
the world isn't going stop the RF from leaking out, like it's 'spozed
ta. Lionheart's tuner is hooked to its backstay with a stainless
strap in a gentle curve held on with a stainless hose clamp.

Now that we got the damned steel cable holdin' the boom up replaced
with something that DOESN'T suck off the HF signal into the mainmast,
it works much better......well, at least until the sun exploded wiping
out the ionosphere....

73 DE W4CSC

NNNN

AR

It isn't the RF leaking out that GTO-15 is used for.....

Real Marine Radiomen use PhospherBronze Antenna Wire and GTO-15
as short jumpers where human contact is possible.......

GTO-15 is, highly insulated stranded copper wire, used to connect
antenna tuners to antennas in the marine enviorment. It has 15000V
insulation to prevent flashovers and arc's to ground, from the high
voltage companents of the voltage feed longwire antennas. The 1"
insulators are designed to move the RF antenna away from the Grounded
Backstay and reduce the RF coupling between these two components.
1" isn't enough to really do the job. 6" would be much better considering
the length of the two components, and their parallel coupling.

GTO-15 is fancy sparkplug wire....

Bruce in alaska
 
H

Harry Krause

Jan 1, 1970
0
Larry said:
Wasn't me. I never heard of GTO-15 before.....??????





Larry W4CSC

"Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"

You'll find a lot of GTO-15 at neon sign shops. It's heavy voltage cable.
 
W

Woody

Jan 1, 1970
0
I see this all the time on cruising boats not most, not many but a
few. I always try to argue with the person that installed it on the
pros and cons but never get anyone that can talk rf to me. best I had
was an extra class ham that just said it works better because I can
hear the difference.

Distributed capacitance should be taken care of by the antenna tuner
(all random length end fed vertical wire antennas on boats have tuners
I think) So I guess the reason is to keep stray rf from coupling and
reflecting back from the backstay. I would think that a ? wavelength
distance from the backstay to the gto-15 should be good. But since you
will be using it on many bands I would guess that at least 1/8
wavelength at the lowest frequency would be someplace to start from.
Maybe about 10 meters separation between backstay and gto-15 may make
a measurable difference. 2 inches of separation, less then 1
electrical degree ROTFLMAO at anyone who says it makes a difference.

If you are talking coax, and it is properly impedance "matched" at both
ends, proximity to objects (metal or not) will have no effect. There is
(should be...) no RF on the outside of the shield.

OTOH...
Most comments reference a single feed wire to the stay. In that case
isolating the wire from nearby objects is very important for proper
function.

Woody
 
K

Kris VK4CPG

Jan 1, 1970
0
It is practically impossible to match coax cable to an end-fed antenna for
various bands, without traps or impedance matching tricks at the end of the
coax. The outer insulation and even the core insulation of coax is normally
not high voltage proof, so don't rely on it, certainly not near an "earthed"
wire.
Special marine antenna cable can be bought but is expensive. I used
multicore green earthing wire and spacers. These can be made of 5cm pieces
of white conduit pipe (UV stabilised) with two holes on each side to fix a
tag to the feeder wire and the backstay. Wrapping around both, fixes it
well. Perhaps shrink tubing would even make it more "professional". The wire
has been there for more than 5 years and the plastic has not deteriorated.
The inside wires were getting black, so soldering on both ends is necessary.
I am now going to replace it by special multicore UV stable HV cable, neatly
tied to the backstay.
It is still the question if spacers are electrically better than tying a
cable close to the backstay. The coupling between the feeder and the rest of
the backstay makes the antenna anyway into an a-symmetrical off-centre fed
thingie that may radiate well on one frequency but miserable on another. The
tuner will make the whole system resonant but that does not guarantee good
radiation or prevent RFI. Sometimes a dummy load would perform the same way.
With spacers, a 600 ohm feeder could be created (at least for some length)
to keep stray radiation at lower levels but it must be symmetrically fed and
commercial tuners don't do that.
Probably the best is trying it out, as there is not much calculation that
can be done. Thick marine antenna cable tied to the backstay makes the
system at least wind and foolproof. And pray for no RFI into the GPS and
mobile phone antennas.
 
G

Gordon Wedman

Jan 1, 1970
0
I doubt the boat in question was using coax. I just didn't know the
correct term to use for this type of wire and used "coax". Subsequent to all
the original discussion I had a closer look at the wire used on my boat
(installed in 1983) and I see that it is, in fact, GTO-15. Says so right on
the insulation.
Now I just need to buy a decent SSB to hook up to the backstay after
selling the old Motorola 11 channel unit.
 

Yachtfunk

Jul 14, 2009
1
Joined
Jul 14, 2009
Messages
1
Standoffs and GTO-15

When installing equipment capable of
transmitting HF frequencies, one needs to
carefully think about where HF is radiated, thus
one needs to decide where certain distances
need to be kept short in order to avoid loss
of power or interference. Connecting the tuner
to the antenna, it is necessary to emphasize
that the feeder is already part of the antenna
– system. Therefore, the tuner will try
electrically to adjust the length of the antenna
- including the length of the feeder - to the
used frequency. At last year’s ARC, we were
surprised to see that many so called “experts”
working for shipyards had installed coax
cable between the tuner and the antenna.
That is one of the major problems that keeps
the tuner from adjusting the antenna system.
A lot of the power emitted on the way to the
insulated backstay will be reflected inside
the coax, back to the tuner and will finally
be diverted to ground. The tuner will never
be able to properly adjust the system unless
appropriate cable is installed. Yachtfunk.com
recommends GTO-15, a high-voltage cable to
connect tuner and antenna. The GTO-15 will
then have to be kept at a distance to the uninsulated
part of the backstay with the help of
standoffs. A feeder directly connected to the
un-insulated backstay would lead to a loss
of power and can cause interferences with
other electrical systems onboard. Basically
we can say that whatever kind of antenna is
used onboard, it should be mounted as far
away from any metal objects on the vessel as
possible for the best performance possible.
Distance also plays an important role with
regard to the installation of the tuner – it should be placed as close as possible to the
ground-plane.

More Info´s by yachtfunk.com

sea u
Joerg
 
Top