On Tue, 23 Aug 2005 22:47:28 +0200, "Meindert Sprang"
wrote:

"Bob" wrote in message
.. .
On Tue, 23 Aug 2005 11:33:18 -0400, Gary Schafer
wrote:
The amount of shielding of coax cable is of little importance in most
typical radio installations.

disagree. with the increasing amount of electronics on boats nowadays,
more shielding is better.

Theorethically yes. In practice, it doesn't matter that much. A shield works
because it creates loops of current, opposite of that in the inner conductor
which keeps the field in.

during transmission. in receiving it acts as a ground.

A practical mesh size on for instance parabolic
antenna's is 1/10 of the wavelength. This will yield a good field
reflection. So on VHF, where the wavelength is about 6 ft, a mesh size of 7
inches would already shield. On many older FM radiostations, "coax" was was
made by an inner conductor surrounded by a "screen" of many (say 20) outer
conductors supported by metal rings.

except many electronics systems operate at freqs far above VHF.


again, disagree. many people report GPS, electronic compass, and
computer problems when they key up their radios. of course some of
this is overload from the antenna, etc. but more shielding on the
cable reduces inteference to and from the radio.

This kind if interference is more likely caused by improper termination
(standing waves), which causes currents to flow on the outside of the
shield. Nothing to do with bad shielding.

several components are responsible for reducing interference.
shielding is one of them. again, it's a matter of selection. why use
58 when superior cables are available?

---------------------------
to see who "wf3h" is, go to "qrz.com"
and enter 'wf3h' in the field

"Bob" wrote in message
...
On Tue, 23 Aug 2005 22:47:28 +0200, "Meindert Sprang"
wrote:
Theorethically yes. In practice, it doesn't matter that much. A shield
works
because it creates loops of current, opposite of that in the inner
conductor
which keeps the field in.

during transmission. in receiving it acts as a ground.

From the cable's point of view, there is no difference between transmission
and reception. Only the power levels are different. The screening principle
works the same.

A practical mesh size on for instance parabolic
antenna's is 1/10 of the wavelength. This will yield a good field
reflection. So on VHF, where the wavelength is about 6 ft, a mesh size of
7
inches would already shield. On many older FM radiostations, "coax" was
was
made by an inner conductor surrounded by a "screen" of many (say 20)
outer
conductors supported by metal rings.

except many electronics systems operate at freqs far above VHF.

Yep. So let's assume the openings in the screen are 1mm. That will still
screen up to 10mm wavelength, aka 30GHz.

Meindert

I just can't help opionionating about PL-259's..... in general.

Hand tightening is not sufficient..... maybe in a test situation, but if you
are going to walk away from them, tightening with your choice of pliers.

Standard PL-259's are not waterproof, and anywhere that safety or
reliability is necessary, they've got to be sealed with something. My
personal favorite is a couple of coats of "Liquid Tape"... available in your
choice of colors.

Someone already mentioned that these connectors, outdoors especially, are
frequently "repaired" or at least work better if taken off and reinstalled
once in a while. It is an eye-opener how many antenna installations suddenly
work a lot better after doing just that.

There is a lot more, but the lawn needs mowing..... NOW!

Old Chief Lynn

"Lynn Coffelt" wrote in message
...
I just can't help opionionating about PL-259's..... in general.

Hand tightening is not sufficient..... maybe in a test situation, but if
you
are going to walk away from them, tightening with your choice of pliers.

Standard PL-259's are not waterproof, and anywhere that safety or
reliability is necessary, they've got to be sealed with something. My
personal favorite is a couple of coats of "Liquid Tape"... available in
your
choice of colors.

Someone already mentioned that these connectors, outdoors especially, are
frequently "repaired" or at least work better if taken off and reinstalled
once in a while. It is an eye-opener how many antenna installations
suddenly
work a lot better after doing just that.

There is a lot more, but the lawn needs mowing..... NOW!

Old Chief Lynn


The PL-259, and all the similar "UHF" connectors were pre-WWII attempts for
a field installable coaxial fitting and they even called them "UHF"
fittings. It is well known they aren't even a constant impedance at RF. I
don't like to see them used above 30 MHZ but realize it is commercial
practice to use them to 200 MHz or so. If you have a Time Domain
Reflectometer handy and a good commercial grade 50 ohm dummy load (Bird,
General Radio, etc), take a look at the impedance bumps as the TDR sweeps
through the PL259. It makes you a believer in type N in a hurry. I recall
Collins radio used the N connector even at HF, e.g., the old KWS-1 SSB
transmitter.
Marine antenna manufacturers such as Shakespeare include a PL-259 and the
appropriate RG-58 or RG-8X (RG-59 size) adapters with their antenna package.
I throw the PL-259s away and use a silver plated PL259 instead. The center
insulation is better, and it takes solder easily. The factory connector is
very difficult to solder and is the cause of many owner installed
intermittent in a marine environment.
3M makes a black paint to coat coax fittings for weather proofing, and I
have worked for various employers who had their favorite technique for
sealing PL-259s, such as 3M paint, RTV with Scotch 88 electrical tape, etc.
My current favorites are Coax Seal putty in tape form or "Tommy Tape"
elastic self adhering tape.
73
Doug K7ABX

I throw the PL-259s away and use a silver plated PL259 instead. The center
insulation is better, and it takes solder easily. The factory connector is
very difficult to solder and is the cause of many owner installed
intermittent in a marine environment.

I second that! I've thrown literally hundreds of Shakespeare PL-259's
away. I felt bad, but a silver plated one with Teflon dielectric were so
much easier to solder!

The Shakespeares could be soldered on a windy day if a small, three
cornered file was used to take off the crummy plating at the bottom of the
groove where the solder holes were. Strictly an emergency procedure, of
course. Grin.

May be "uban legend" but a "tech" friend said when patch cable problems
cropped up (he spoke of BNC and TNC's) an experienced guy with a TDR could
tell which of their techs installed each connector.

Old Chief Lynn

In article t,
"Doug" wrote:

"Lynn Coffelt" wrote in message
...
I just can't help opionionating about PL-259's..... in general.

Hand tightening is not sufficient..... maybe in a test situation, but if
you
are going to walk away from them, tightening with your choice of pliers.

Standard PL-259's are not waterproof, and anywhere that safety or
reliability is necessary, they've got to be sealed with something. My
personal favorite is a couple of coats of "Liquid Tape"... available in
your
choice of colors.

Someone already mentioned that these connectors, outdoors especially, are
frequently "repaired" or at least work better if taken off and reinstalled
once in a while. It is an eye-opener how many antenna installations
suddenly
work a lot better after doing just that.

There is a lot more, but the lawn needs mowing..... NOW!

Old Chief Lynn


The PL-259, and all the similar "UHF" connectors were pre-WWII attempts for
a field installable coaxial fitting and they even called them "UHF"
fittings. It is well known they aren't even a constant impedance at RF. I
don't like to see them used above 30 MHZ but realize it is commercial
practice to use them to 200 MHz or so. If you have a Time Domain
Reflectometer handy and a good commercial grade 50 ohm dummy load (Bird,
General Radio, etc), take a look at the impedance bumps as the TDR sweeps
through the PL259. It makes you a believer in type N in a hurry. I recall
Collins radio used the N connector even at HF, e.g., the old KWS-1 SSB
transmitter.
Marine antenna manufacturers such as Shakespeare include a PL-259 and the
appropriate RG-58 or RG-8X (RG-59 size) adapters with their antenna package.
I throw the PL-259s away and use a silver plated PL259 instead. The center
insulation is better, and it takes solder easily. The factory connector is
very difficult to solder and is the cause of many owner installed
intermittent in a marine environment.
3M makes a black paint to coat coax fittings for weather proofing, and I
have worked for various employers who had their favorite technique for
sealing PL-259s, such as 3M paint, RTV with Scotch 88 electrical tape, etc.
My current favorites are Coax Seal putty in tape form or "Tommy Tape"
elastic self adhering tape.
73
Doug K7ABX



Hey Doug, Are you guys using the AMP Teflon Insulation PL-259s, these
days? Thank the Maker, that some smart guy invented Putty Tape.....


Bruce in alaska
--
add a 2 before @

(Bob) wrote in
:

communications is one area where bigger is better, in this case.



Next thing you know, we'll be running 3 1/2" rigid hardline sections up the
mast behind the jib.....trying to get those numbers down.....

Bull****. RG-58A/U works just fine from the top of a 55' mainmast to the
Icom M602 at the nav station.

From Charleston, I can hear JAX USCG broadcasts and talk to Savannah....(c;

Rigid hardline won't go any further than the radio horizon....

For you hams.....

A young ham was trying to figure out how to get his 75 meter dipole to hold
up RG-8 over the back yard. It kept breaking the antenna wire when the
wind blew. So, I put up a 75 meter dipole and used RG-174A/U to feed its
center about 60' long. Way too funny to see the look on his face when he
saw the coax plugged into my station antenna switch. Of course, at 4 Mhz,
about any coax is just fine. This tiny coax survived our tests up to about
200 watts when it melted....(c;

--
Larry

I have some old friends, even friends who operated CW on subs in WW2,
who've just become enthralled with PSK31 digital mode. If your
transceiver
has VOX, you don't even need any interface box expense. A 10K pot to
control drive from the soundcard to the mic jack is plenty. Hookup is
almost too easy.

I use Winwarbler, which can copy three simultaneous stations on slightly
different frequencies. PSK is SUPERIOR to the finest CW station. It will
copy a DX PSK station so far into the noise you can't even tell there are
tones in the noise, much less copy Morse from it if he were sending in
Morse. PSK stations, to reduce interference in the 3Khz bandwidth the
gentlemen's agreement puts them on at 14.070, usually use only 10 or 20
watts of power, even on the other side of the planet. It's uncanny that a
cheap little soundcard can pull those tones out of the noise with such
accuracy.

Ham radio hasn't done much "inventing" in the past 30 years, but PSK is a
ham radio invention that should be enjoyed by all. Tune your HF to 14.070
SSB and listen for tiny warbling tones. Plug the headphone jack into the
LINE IN on your computer and run the Winwarbler software you get from:
http://www.qsl.net/winwarbler/
Point your mouse at any little trace in the waterfall display and click on
it. Winwarbler starts decoding instantly in the current window. Click
the
next window and pick another signal trace. It's that easy...(c;
Instructions for use and installation are on the webpage. Simply amazing
mode of RTTY comms between stations, with the simplest of equipment. Pick
a trace you can hardly make out in the display and click on it...watch it
type...(c;

--
Larry

Larry! For gosh sakes, it really works. Maybe not exactly error free
down in the noise, but there is decoding that my CW skills will never match!
I spent two evenings finding the line out volume control for my sound
card!....... had no snow on the waterfall, but the instant the noise
appeared, there were several signals quite apparent!
I have no transceiver, so the magic will have to wait, but "reading the
mail" with my FRG-100 is pretty exciting.
Thanks for the tip!

Old Chief Lynn..... RG-213 Forever! (cable guy's underground hardline ain't
too bad either...... but not around salt water)

"Lynn Coffelt" wrote in
Glad you got it going. PSK is the finest mode that's happened to ham radio
since SSB. It's simply amazing to realize those stations you are printing
are only running 10-20 watts on the other side of the planet in these awful
HF propagation conditions....

They're working on improving this with changes!

:

Larry! For gosh sakes, it really works. Maybe not exactly error
free
down in the noise, but there is decoding that my CW skills will never
match!
I spent two evenings finding the line out volume control for my
sound
card!....... had no snow on the waterfall, but the instant the noise
appeared, there were several signals quite apparent!
I have no transceiver, so the magic will have to wait, but
"reading the
mail" with my FRG-100 is pretty exciting.
Thanks for the tip!

Old Chief Lynn..... RG-213 Forever! (cable guy's underground hardline
ain't too bad either...... but not around salt water)





--
Larry

"Bob" wrote in message
...
On Tue, 16 Aug 2005 13:47:27 -0400, Larry wrote:

( Mika) wrote in :

Need to install a new VHF antenna to a sailboat.

Put a 1/2 wave antenna as high as you can get it. 2000 meters is great!
but the top of the tallest mast will do just fine.

When you're screaming for help in a sinking boat, you can never have an
antenna that's too high! The altitude of the mast antenna more than makes
up for the length of the cabling losses. With a 25W Icom and 1/2
wavelength Metz whip at 55 ft on the other end of 30 meters of RG-58/U
coax, Lionheart can call the US Coast Guard station way out of sight of
land.


but never, never, never ever use rg 58 cable. it's not shielded
properly. it has high loss.

Many Marine VHF antennas have the cable moulded in and it's RG-58 so the
argument between RG-58 and RG-8 is purley acedemic.
Unlike the radio Ham, where every last inch of tx distance is a feather in
the cap and one up on the next person, on a boat it's just a tool, boating
is the hobby.