On Sep 5, 1:12 pm, Highland Ham
wrote:
Is it possible to check the quality of a coax connection to a PL259
plug without taking the plug apart - i.e. simply by using a
multimeter?

Hi Andy,

With both ends in your lap:
shells, end to end - very low Ohms;
pins, end to end - very low Ohms;
shell to pin, either end - infinite Ohms.

===========================
The above is an electrical contact/insulation (DC) check

To check the quality of the complete coax cable including the plug(s)
a 'coax loss' check especially when operating at the higher frequencies
is important.

Some antenna analysers (like the MFJ 259/269 ) have this coax loss
measuring facility. These instruments enable the user to change
frequency which shows the overall quality of coax + fitted plugs.

The best type of PL259 plug is the one with a cable entry arrangement as
in N-type plugs . This provides an excellent and simple braid connection
,without having to apply heat other than soldering the centre conductor
to the top of the pin .
These plugs are somewhat more expensive than traditional PL259 plugs
(equivalent US$ 6 in the UK) but imho it is worth the expenditure.

Frank GM0CSZ / KN6WH

All

More on the nature of the problem. I have basically fitted a 1/2 size
G5RV. Its fitted at 30 ft high between a pole at the end of the yard
and the chimney at approx 30 ft high. The ladder line falls pretty
much vertically except for the very end where i have had to divert it
away from a steel cast iron style balcony which surrounds a roof
terrace on the first floor. I figured it would not be good to brush
alongside the balcony as its metal.

Anyway, i am getting some very weird SWR readings even when i am using
my automatic ATU (LDG Z-100. These range from close to 1.1:1 on
40metres all the way up to 3.1: 1 in the middle of the 20 metre band.
I am trying to work out where the problem may lie. So far i have come
up wiith:

1) its just the way the antenna works and the ATU cant do any better?
2) the ATU is not working properly (but it seems to get a decent match
elsewhere)?
3) there is a problem with the plugs (would this appear to make a
difference only on some frequencies)?
4) somehow the stell balcony / balustrade is causing a problem even
though i am keeping the ladder line approx 12 inches away from it.
Also would this only cause a problem on 20M?
5) running the coax along the steel balustratde and into the house is
causing a problem (is this possible)?

Confounding factor is that it seems to be working ok even with the
high SWR and i have made some decent contacts on both 40 and 20
metres.

I thought i should start with the plugs but any other thoughts welcome
- all very odd!!

Regards

Andy

On Wed, 05 Sep 2007 08:04:32 -0700, Andiroo
wrote:

1) its just the way the antenna works and the ATU cant do any better?

Probably.

2) the ATU is not working properly (but it seems to get a decent match
elsewhere)?

Too complex an answer for a non-problem, no.

3) there is a problem with the plugs (would this appear to make a
difference only on some frequencies)?

Not as you describe things.

4) somehow the stell balcony / balustrade is causing a problem even
though i am keeping the ladder line approx 12 inches away from it.
Also would this only cause a problem on 20M?

Nope, 12 inches is fine.

5) running the coax along the steel balustratde and into the house is
causing a problem (is this possible)?

Only if the "problem" changes with moving the coax.

Confounding factor is that it seems to be working ok even with the
high SWR and i have made some decent contacts on both 40 and 20
metres.

Well! that certainly sucks big time.

I thought i should start with the plugs but any other thoughts welcome
- all very odd!!

Actually, given you can receive and transmit, the plugs was probably
the worst guess. All in all this is a case of losing your keys in the
road at night, and spending all your time searching under the street
light.

Are you, perhaps, under the impression that a G5RV (or any variation
thereof) "should perform better?"

73's
Richard Clark, KB7QHC

Andiroo wrote in news:1189004672.355388.8520
@k79g2000hse.googlegroups.com:

....
All

More on the nature of the problem. I have basically fitted a 1/2 size
G5RV. Its fitted at 30 ft high between a pole at the end of the yard
and the chimney at approx 30 ft high. The ladder line falls pretty
much vertically except for the very end where i have had to divert it
away from a steel cast iron style balcony which surrounds a roof
terrace on the first floor. I figured it would not be good to brush
alongside the balcony as its metal.

Anyway, i am getting some very weird SWR readings even when i am using
my automatic ATU (LDG Z-100. These range from close to 1.1:1 on
40metres all the way up to 3.1: 1 in the middle of the 20 metre band.
I am trying to work out where the problem may lie. So far i have come
up wiith:
....

You might find my article on optimising the G5RV of interest. You will
need to scale for a half size G5RV, so scale the frequency axis of the
graph times two, and when it tells you to check for an electrical half
wave of open wire line at 14Mhz, you need to do it at 28Mhz etc. The
article is at http://www.vk1od.net/G5RV/optimising.htm .

After some basic DC tests for proper and reliable connection, no short
circuits etc, next is some more serious RF evaluation of the antenna
system.

The commonest reason for a G5RV to perform worse than expected is that
the open wire line is an incorrect length, usually due to not properly
considering its velocity factor. (If you purchased a kit, as so many
people seem to do nowadays, you would hope that the supplier got this
correct... but?) Next is the length of the dipole which is often
regarded as not affected by its environment. (This applies to a
commercial kit as well as a DIY G5RV.) A tape measure is the start of
setting up a G5RV, not the end.

Owen

On Sep 5, 9:49 pm, Owen Duffy wrote:
Andiroo wrote in news:1189004672.355388.8520
@k79g2000hse.googlegroups.com:

... All

More on the nature of the problem. I have basically fitted a 1/2 size
G5RV. Its fitted at 30 ft high between a pole at the end of the yard
and the chimney at approx 30 ft high. The ladder line falls pretty
much vertically except for the very end where i have had to divert it
away from a steel cast iron style balcony which surrounds a roof
terrace on the first floor. I figured it would not be good to brush
alongside the balcony as its metal.

Anyway, i am getting some very weird SWR readings even when i am using
my automatic ATU (LDG Z-100. These range from close to 1.1:1 on
40metres all the way up to 3.1: 1 in the middle of the 20 metre band.
I am trying to work out where the problem may lie. So far i have come
up wiith:

...

You might find my article on optimising the G5RV of interest. You will
need to scale for a half size G5RV, so scale the frequency axis of the
graph times two, and when it tells you to check for an electrical half
wave of open wire line at 14Mhz, you need to do it at 28Mhz etc. The
article is athttp://www.vk1od.net/G5RV/optimising.htm.

After some basic DC tests for proper and reliable connection, no short
circuits etc, next is some more serious RF evaluation of the antenna
system.

The commonest reason for a G5RV to perform worse than expected is that
the open wire line is an incorrect length, usually due to not properly
considering its velocity factor. (If you purchased a kit, as so many
people seem to do nowadays, you would hope that the supplier got this
correct... but?) Next is the length of the dipole which is often
regarded as not affected by its environment. (This applies to a
commercial kit as well as a DIY G5RV.) A tape measure is the start of
setting up a G5RV, not the end.

Owen

Owen

Yes it was a commercial antenna and i guess the last thing on my mind
was measuring its length? mmmm.... now you got me thinking, Given this
was far from the cheapest G5RV and from W&S rather than some unknown
on ebay i would have hoped it was 51ft as described. Would i need to
source a willing local fellow to come around with an antenna analyser
or are there some simple tests. I will read the article and give this
some more thought. Thanks for the ideas.

Andy
M3ZLN