I am modelling a Double Bazooka constructed of RG58C/U, and am interested
in a method of estimating the effective RF resistance of the outer of the
outer conductor compared to a round copper conductor of the same diameter.

The structure loss calculated by NEC-2 is about 2%, so it is a fairly small
quantity.

The model so far is of a Double Bazooka resonant at 3.6MHz at 10m height
over average ground, constructed entirely of Belden 8262 (RG58C/U), and fed
with 25m of the same line. The model ignores the effect of the jacket on
the radiator, and assumed that it is a round copper conductor of the same
diameter as the sheild of the coax. The draft results at at
http://www.vk1od.net/DoubleBazooka/Fig01.gif .

Owen

On May 11, 4:42 pm, Owen Duffy wrote:
I am modelling a Double Bazooka constructed of RG58C/U, and am interested
in a method of estimating the effective RF resistance of the outer of the
outer conductor compared to a round copper conductor of the same diameter.

The structure loss calculated by NEC-2 is about 2%, so it is a fairly small
quantity.

The model so far is of a Double Bazooka resonant at 3.6MHz at 10m height
over average ground, constructed entirely of Belden 8262 (RG58C/U), and fed
with 25m of the same line. The model ignores the effect of the jacket on
the radiator, and assumed that it is a round copper conductor of the same
diameter as the sheild of the coax. The draft results at athttp://www.vk1od.net/DoubleBazooka/Fig01.gif.

Owen

Hi Owen,

A fellow from Times Microwave, I believe it was, wrote an article that
was published in one of the electronics/RF journals back about ten
years ago, about coax, including loss. He included comments about
braids and stranded conductors, I believe. I went looking for the
article some time after I read it, and never could find it again.
Unfortunately, I also never got a positive response from Times about
it when I asked. But if you trust my memory, you can try a value of
about 7% increase in RF resistance as compared with a smooth round
conductor, for braid. That's at best an estimate, but it probably
doesn't matter all _that_ much for what you are doing. I expect it
depends on the angle of the brading, and to some extent on the
frequency; I believe the 7% is for frequencies whose wavelength was
much longer than the "pitch" of the braid, which clearly would be the
case for your antenna.

Hope this is some help and not too much arm-waving for your purpose.

You could, of course, get an idea by comparing the loss for various
types of coax where the difference is in the outer conductor: braid
vs solid. But because the outer is typically such a small part of the
total loss, the estimate's accuracy would be limited.

Cheers,
Tom

K7ITM wrote in
oups.com:

On May 11, 4:42 pm, Owen Duffy wrote:
I am modelling a Double Bazooka constructed of RG58C/U, and am
interested in a method of estimating the effective RF resistance of
the outer of the outer conductor compared to a round copper conductor
of the same diameter.

The structure loss calculated by NEC-2 is about 2%, so it is a fairly
small quantity.

The model so far is of a Double Bazooka resonant at 3.6MHz at 10m
height over average ground, constructed entirely of Belden 8262
(RG58C/U), and fed with 25m of the same line. The model ignores the
effect of the jacket on the radiator, and assumed that it is a round
copper conductor of the same diameter as the sheild of the coax. The
draft results at athttp://www.vk1od.net/DoubleBazooka/Fig01.gif.

Owen

Hi Owen,

A fellow from Times Microwave, I believe it was, wrote an article that
was published in one of the electronics/RF journals back about ten
years ago, about coax, including loss. He included comments about
braids and stranded conductors, I believe. I went looking for the
article some time after I read it, and never could find it again.
Unfortunately, I also never got a positive response from Times about
it when I asked. But if you trust my memory, you can try a value of
about 7% increase in RF resistance as compared with a smooth round
conductor, for braid. That's at best an estimate, but it probably
doesn't matter all _that_ much for what you are doing. I expect it
depends on the angle of the brading, and to some extent on the
frequency; I believe the 7% is for frequencies whose wavelength was
much longer than the "pitch" of the braid, which clearly would be the
case for your antenna.

Ok.

I did try a sensitivity analysis by modelling aluminium (which IIRC has a
skin resistance of about double copper) and it didn't make much
difference to the outcome.


Hope this is some help and not too much arm-waving for your purpose.

Thanks.


You could, of course, get an idea by comparing the loss for various
types of coax where the difference is in the outer conductor: braid
vs solid. But because the outer is typically such a small part of the
total loss, the estimate's accuracy would be limited.

I did think of that, but my estimate is that the outer conductor of such
a cable contributes something like 20% of the R component of an RLGC
model, and I thought it getting to great a reach to try to deconstruct
the total R, deducting the inner R, and then working out a factor for the
inner of the outer R against an ideal conductor of that inner diameter.
Others have hinted at times that I may have gone too far in translation
of published cable specs into an RLGC model.

BTW, the graph has changed, I doubled an admittance instead of halving it
in the code, so the stub was having more effect that it really does.

Thanks again.

Owen

have you tried measuring the rf resistorance?

On May 11, 5:52 pm, Owen Duffy wrote:
K7ITM wrote groups.com:





On May 11, 4:42 pm, Owen Duffy wrote:
I am modelling a Double Bazooka constructed of RG58C/U, and am
interested in a method of estimating the effective RF resistance of
the outer of the outer conductor compared to a round copper conductor
of the same diameter.

The structure loss calculated by NEC-2 is about 2%, so it is a fairly
small quantity.

The model so far is of a Double Bazooka resonant at 3.6MHz at 10m
height over average ground, constructed entirely of Belden 8262
(RG58C/U), and fed with 25m of the same line. The model ignores the
effect of the jacket on the radiator, and assumed that it is a round
copper conductor of the same diameter as the sheild of the coax. The
draft results at athttp://www.vk1od.net/DoubleBazooka/Fig01.gif.

Owen

Hi Owen,

A fellow from Times Microwave, I believe it was, wrote an article that
was published in one of the electronics/RF journals back about ten
years ago, about coax, including loss. He included comments about
braids and stranded conductors, I believe. I went looking for the
article some time after I read it, and never could find it again.
Unfortunately, I also never got a positive response from Times about
it when I asked. But if you trust my memory, you can try a value of
about 7% increase in RF resistance as compared with a smooth round
conductor, for braid. That's at best an estimate, but it probably
doesn't matter all _that_ much for what you are doing. I expect it
depends on the angle of the brading, and to some extent on the
frequency; I believe the 7% is for frequencies whose wavelength was
much longer than the "pitch" of the braid, which clearly would be the
case for your antenna.

Ok.

I did try a sensitivity analysis by modelling aluminium (which IIRC has a
skin resistance of about double copper) and it didn't make much
difference to the outcome.



Hope this is some help and not too much arm-waving for your purpose.

Thanks.



You could, of course, get an idea by comparing the loss for various
types of coax where the difference is in the outer conductor: braid
vs solid. But because the outer is typically such a small part of the
total loss, the estimate's accuracy would be limited.

I did think of that, but my estimate is that the outer conductor of such
a cable contributes something like 20% of the R component of an RLGC
model, and I thought it getting to great a reach to try to deconstruct
the total R, deducting the inner R, and then working out a factor for the
inner of the outer R against an ideal conductor of that inner diameter.
Others have hinted at times that I may have gone too far in translation
of published cable specs into an RLGC model.

BTW, the graph has changed, I doubled an admittance instead of halving it
in the code, so the stub was having more effect that it really does.

Thanks again.

Owen- Hide quoted text -

- Show quoted text -