Peter Hendra wrote in
:

Oh, and what is an optimum length and diameter - covered in plastic or
bare? - I know, only a project manager would want precision such as
this.

Thanks for all of this Larry. I shall follow your advice.



Optimum length would be 5% longer than 1/4 wavelength of the frequency
you are operating on. 1/4 wavelength in meters is 75.7/frequency in Mhz.

So, if we are on 6 Mhz, for instance, we get 75.7/6 x 1.05 = 13.2 meters.

But, because the radiating element ISN'T a proper length and we are using
a tuner, just make it LONG and the tuner will tune out the reactance and
match it up...

--------------------------------------------------

On another issue you have brought up, you said you had two backstays in
parallel, one with insulators that is the antenna and one that is not and
is solidly connected to the mast, right??

If this is so, in close proximity to the radiating element, that second
backstay is simply absorbing a major part of your radiation from the real
antenna, greatly reducing your actual field strength at some remote
receiver. We can't stop induced, out of phase, RF currents in any of the
rigging, but you can reduce it, greatly, giving you a nicely stronger
signal.

If these backstays are as I think, please consider putting insulators at
equal distance in BOTH backstays,not just one. Then, run a jumper
between upper end of the bottom insulators, effectively paralleling them.
Feed the tuner into the CENTER of this jumper, which can also be two
equal-length wires from the HV output of the tuner to the two insulator
feedpoints. The effect of doing this is a radiator that is MUCH greater
in "virtual diameter", both radiating IN PHASE, which aids their field
strength. Instead of the second backstay absorbing the signal, it will
create more signal, in phase. If your tuner is below them, you can
either make a T to feed the two backstays or just Y them out of the
tuner, itself, with EQUAL LENGTH conductors to preserve their phase
relationship.

Larry
--
Antennas R Us
If it doesn't glow blue after dark, power output is down.....(c;

Thanks Larry,
You are making my simple mind spin.

Seriously though, I am truly appreciative of your advice in this and
all matters. What you say about backstay aerials makes sense and I
shall do as you suggest. What I would really like, as do most others,
is long range voice comms. If anything reasonable helps in any way, I
will do it. There is nothing quite so annoying as to not be able to
receive an interpretable weather fax because of poor reception.

I'll add the ground from my stays. By the way, I neglected to tell
that I have a painted box section wooden mast, deck stepped. Forestay,
backstays and capshrouds are electrically connected due to their
attachment at the head of the mast. There is an aluminium sailtrack
which has no connection. Should this be a factor for consideration?

My specific area of small expertise over the past few years has been
packet data and such as better compression algorithms, up and down
linking to comms satellites, and the problem of latency or delay in
resending packets - solved by a really neat way of transmitting two
packet streams, with a slight delay on the second. If one packet
address is missing or denatured in some way, "it" merely grabs its
copy from the second incoming stream without having to ask the
originator for a resend and the consequent latency or time delays
whilst waiting - speeds it up no end. Probably been invented before
somewhere else but that sort of thing happens all the time. The
tracking system can track all of our active patrol boats as well as
Indonesia's ( and give postion, direction, speed and a lot of other
data in sub minute real time as well as sending and receiving text
messages and orders. If we needed to, we could add engine revs,
temperature and a lot of other really uinnecessary stuff.

Even though mobile phones are just glorified two channel radios, So
far as radio propagation (and most of the rest of it) has failed to
lodge in my brain successfully.

Thanks again for being so helpful and for freely disseminating your
experienced advice to those such as me whom you will probably never
meet.

cheers
Peter

On Fri, 27 Apr 2007 16:33:31 +0000, Larry wrote:

Peter Hendra wrote in
:

Oh, and what is an optimum length and diameter - covered in plastic or
bare? - I know, only a project manager would want precision such as
this.

Thanks for all of this Larry. I shall follow your advice.



Optimum length would be 5% longer than 1/4 wavelength of the frequency
you are operating on. 1/4 wavelength in meters is 75.7/frequency in Mhz.

So, if we are on 6 Mhz, for instance, we get 75.7/6 x 1.05 = 13.2 meters.

But, because the radiating element ISN'T a proper length and we are using
a tuner, just make it LONG and the tuner will tune out the reactance and
match it up...

--------------------------------------------------

On another issue you have brought up, you said you had two backstays in
parallel, one with insulators that is the antenna and one that is not and
is solidly connected to the mast, right??

If this is so, in close proximity to the radiating element, that second
backstay is simply absorbing a major part of your radiation from the real
antenna, greatly reducing your actual field strength at some remote
receiver. We can't stop induced, out of phase, RF currents in any of the
rigging, but you can reduce it, greatly, giving you a nicely stronger
signal.

If these backstays are as I think, please consider putting insulators at
equal distance in BOTH backstays,not just one. Then, run a jumper
between upper end of the bottom insulators, effectively paralleling them.
Feed the tuner into the CENTER of this jumper, which can also be two
equal-length wires from the HV output of the tuner to the two insulator
feedpoints. The effect of doing this is a radiator that is MUCH greater
in "virtual diameter", both radiating IN PHASE, which aids their field
strength. Instead of the second backstay absorbing the signal, it will
create more signal, in phase. If your tuner is below them, you can
either make a T to feed the two backstays or just Y them out of the
tuner, itself, with EQUAL LENGTH conductors to preserve their phase
relationship.

Larry

Peter Hendra wrote in
:

Seriously though, I am truly appreciative of your advice in this and
all matters. What you say about backstay aerials makes sense and I
shall do as you suggest. What I would really like, as do most others,
is long range voice comms. If anything reasonable helps in any way, I
will do it. There is nothing quite so annoying as to not be able to
receive an interpretable weather fax because of poor reception.


Whatever else you can do to move as much of the suspended metal away from
the radiating antenna element is of most importance in creating more
field strength at the remote receiver.

When Geoffrey first got Lionheart, the mainmast backstay on the ketch
goes from the rear of the center cockpit right up in parallel with the
boom lift, which WAS a stainless steel cable attached to the mast. If
the boat were close hauled, that cable was only a couple of feet from the
radiating backstay and just sucked the signal the transmitter was putting
out right out of the air. We replaced it with a proper, non-conductive,
line and got rid of the mainsail problem. It matters not where the main
is sheeted to the transmission, now.

I also made the backstay antenna BIGGER, longer, with a capacitor hat
top, because I find we use the lower HF frequencies more often. The
triattic between the masts was insulated fore and aft making a flat top
insulated wire. I insisted on the highest voltage insulators because at
the top end of every HF antenna, no matter what frequency you are on,
there is no current, only very high voltage at the top. I then added a
small cable from the upper end of the insulated backstay antenna (below
the upper insulator, of course) to the center of the triattic right above
it, creating a longer antenna with a capacitor hat top.

http://www.cebik.com/gp/cp-th.html
Notice the radiation pattern graph on this webpage of a vertical dipole,
a 1/4 wave vertical against a ground plane (that ocean ground we want)
and how the radiation pattern is much more HORIZONTAL, out towards that
remote station we are trying to contact, with the addition of the
triattic capacitor hat. Anything we can do to lower the vertical's too-
high radiation angle will make our signal much stronger out over the
horizon as it will lower the angle of attack on the ionosphere.

I've been playing with antennas since I was 10. I've been burned playing
with antennas since I was 11....the day the first ham transmitter was
operated...(c; That was 1957...a great year for ham radio at the peak of
the sunspot cycle maximum.

Larry W4CSC - proof positive RF ISN'T hazardous to your health.
I'm still being burned playing with antennas...(c;
--

Peter Hendra wrote in
:

I'll add the ground from my stays. By the way, I neglected to tell
that I have a painted box section wooden mast, deck stepped. Forestay,
backstays and capshrouds are electrically connected due to their
attachment at the head of the mast. There is an aluminium sailtrack
which has no connection. Should this be a factor for consideration?


I'd feel better if you'd add a smooth metal cap at the top of the mast to
bleed off static buildup before it causes a strike.

We've learned a lot since the "lightning rod" days, one of the worst
things ever done to protect buildings from lightning. Remember those
sharp-pointed lightning rods that sprayed electrons into the air to
ionize it and GIVE the clouds a path to ground....right at the top of the
flammable barn roof? This was NOT the way to protect buildings!

Today, lightning systems use a grounded, smooth copper flashing that
distributes the electrons along a smooth, long surface to release them
over as wide an area as possible. A pointy grounded thingy ATTRACTS
lightning because there is a concentrated stream of electrons spraying
off the point, ionizing the air above the point...exactly what the cloud
is looking for.

If there's some kind of metal ring at the top of the mast that's grounded
by the various shrouds and stays, that's great. A metal cap that can
take a pretty good strike, might also keep a hit from boiling the sap in
the mast, creating a steam explosion and putting you out of the sailing
business. This alone makes a mast top bypass cap a good thing.

Larry
--

If there's some kind of metal ring at the top of the mast that's grounded
by the various shrouds and stays, that's great. A metal cap that can
take a pretty good strike, might also keep a hit from boiling the sap in
the mast, creating a steam explosion and putting you out of the sailing
business. This alone makes a mast top bypass cap a good thing.

Larry

yes, it is just as you describe, but this generates another question
(sorry). I had often thought of putting a pointed copper rod on top
grounded to the stays as per many books and articles on the matter. I
have never done so because I believed that it would act as an
attractant, rather like Benjamin Franklin's key on the kite string.

Also what got hit first during the lightning strike in Malaysia - the
day we went back into the water before setting out across the Indian
Ocean mind you - was the VHF aerial. the question is - does the damned
thing act as a lightning attractor as it is the highest thing there?

cheers
Peter

Peter Hendra wrote in
:

Ocean mind you - was the VHF aerial. the question is - does the damned
thing act as a lightning attractor as it is the highest thing there?



Yes, it will. But, that's the best place for the best VHF coverage,
unfortunately. Our main antenna got hit, so I moved both of the VHF
antennas to an L bracket in the shadow of the shrouds down the side of the
mast a ways. The VHF antennas are about 4' down the mast, out away from it
about 24 inches between the mast and the shroud, sorta centered. It's
always a compromise, but it seems to work as well there as it did on top,
exposed to the blast. VHF only has to reach to the horizon, you know, as
it's incapable of going further than that radio horizon just over the
visual one. If it meets that requirement, it's fine.



Larry
--

On Sun, 29 Apr 2007 17:53:07 +0000, Larry wrote:


Again, Thanks for this Larry.
I shall do this also, tomorrow morning. It is only a matter of moving
it down.

The one that got hit just vapourised. The replacement I took off here
to paint the mast - it was one of those clamp in wire ones. Spent two
hours hunting for it and decided that it was cheaper to buy a new one.

cheers
Peter
Peter Hendra wrote in
:

Ocean mind you - was the VHF aerial. the question is - does the damned
thing act as a lightning attractor as it is the highest thing there?



Yes, it will. But, that's the best place for the best VHF coverage,
unfortunately. Our main antenna got hit, so I moved both of the VHF
antennas to an L bracket in the shadow of the shrouds down the side of the
mast a ways. The VHF antennas are about 4' down the mast, out away from it
about 24 inches between the mast and the shroud, sorta centered. It's
always a compromise, but it seems to work as well there as it did on top,
exposed to the blast. VHF only has to reach to the horizon, you know, as
it's incapable of going further than that radio horizon just over the
visual one. If it meets that requirement, it's fine.



Larry

On Fri, 27 Apr 2007 16:33:31 +0000, Larry wrote:

Hi Larry,

On another issue you have brought up, you said you had two backstays in
parallel, one with insulators that is the antenna and one that is not and
is solidly connected to the mast, right??

Correct. as advised by a rigger who was using a rule of thumb, the top
insulator is 3 feet down from the seperation point.

If this is so, in close proximity to the radiating element, that second
backstay is simply absorbing a major part of your radiation from the real
antenna, greatly reducing your actual field strength at some remote
receiver. We can't stop induced, out of phase, RF currents in any of the
rigging, but you can reduce it, greatly, giving you a nicely stronger
signal.

If these backstays are as I think, please consider putting insulators at
equal distance in BOTH backstays,not just one. Then, run a jumper
between upper end of the bottom insulators, effectively paralleling them.
Feed the tuner into the CENTER of this jumper, which can also be two
equal-length wires from the HV output of the tuner to the two insulator
feedpoints. The effect of doing this is a radiator that is MUCH greater
in "virtual diameter", both radiating IN PHASE, which aids their field
strength. Instead of the second backstay absorbing the signal, it will
create more signal, in phase. If your tuner is below them, you can
either make a T to feed the two backstays or just Y them out of the
tuner, itself, with EQUAL LENGTH conductors to preserve their phase
relationship.

Larry