"Gordon Wedman" wrote:

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

Standoffs are highly recommended to eliminate coupling/signal loss between the
leadin and the backstay below the insulators. I made mine by running plastic
wire ties through shrink wrap tubing-a loop around the backstay, through the
tubing, a loop around the wire. About 2" long is good. Not coax at this point,
but High Voltage wire, BTW. Easy to do, and does help performance.

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 ¼ 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.





sded wrote in message . ..
"Gordon Wedman" wrote:

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

Standoffs are highly recommended to eliminate coupling/signal loss between the
leadin and the backstay below the insulators. I made mine by running plastic
wire ties through shrink wrap tubing-a loop around the backstay, through the
tubing, a loop around the wire. About 2" long is good. Not coax at this point,
but High Voltage wire, BTW. Easy to do, and does help performance.

In article ,
says...
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.





sded wrote in message . ..
"Gordon Wedman" wrote:

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

Standoffs are highly recommended to eliminate coupling/signal loss between the
leadin and the backstay below the insulators. I made mine by running plastic
wire ties through shrink wrap tubing-a loop around the backstay, through the
tubing, a loop around the wire. About 2" long is good. Not coax at this point,
but High Voltage wire, BTW. Easy to do, and does help performance.


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

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.
----
Kris
VK4CPG s/v Marin Hedon

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.

"Woody" wrote in message
tt.net...
In article ,
says...
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.





sded wrote in message
. ..
"Gordon Wedman" wrote:

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

Standoffs are highly recommended to eliminate coupling/signal loss
between the
leadin and the backstay below the insulators. I made mine by
running plastic
wire ties through shrink wrap tubing-a loop around the backstay,
through the
tubing, a loop around the wire. About 2" long is good. Not coax at
this point,
but High Voltage wire, BTW. Easy to do, and does help performance.


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