How much can the impedance of coax vary from its characteristic impedance?
 

" wrote in
oups.com:

I use RG6 quite a bit for ham work, and the cable I buy uses a HDC
centre conductor. I would avoid CCS for lower HF.

For what it's worth, I looked up the specs on the Carol C5785 that is
locally available at Home Depot here in the States. It's quad-shield
RG-6 and they list the losses down to 1MHz

1MHz .26dB/100ft
10MHz .81dB/100ft
50MHz 1.46dB/100ft

According to your calculator for RG-6/U it should be
.19
.6
1.37


Dan, You didn't say which of the RG6 cables you used. The figures you
quote are very similar to Belden 1189A. In respect of 1189A, note that
the regression model is based on data points from 55MHz to 1000MHz. That
is either because that is what Belden supplied, or it could be that I
excised some low frequency data points that were a bad fit to the model.

Beware of results where the estimate is an extrapolation. (The frequency
range is red when the estimate is an extraplation.)

Owen

How much can the impedance of coax vary from its characteristic impedance?
 

"Roy Lewallen" wrote in message
...
Tam/WB2TT wrote:

If you are going to buy new coax, might as well get something decent. I
used RG11 FOAM for a 1/4 wave transformer at 3.8 MHz, and it worked per
theory.

I think you were lucky. I've found that the velocity factor and
characteristic impedance of foam dielectric coax, even quality coax, to
vary a lot more than solid dielectric cable. Apparently they don't have
very good control over the foam density.

Roy Lewallen, W7EL

I didn't have the exact Vp number for the SIW cable; so, I trimmed it.
Length came out reasonable, though. If I measure a 50 Ohm load through the
cable, my MFJ269 reads 102/J0 at resonance. A little on the low side, but
probably within tolerance. If it was not raining outside, I would measure
the cable to see what exact length I ended up with. Bottom line is that my
(late) 75 m loop did have an SWR of 1.1:1 at resonance.

Tam/WB2TT

How much can the impedance of coax vary from its characteristic impedance?
 

The RG-59/U I am using does in fact have a stranded center conductor.
I am using RG-59/U because I am feeding a vertical (quad) loop on the
vertical side and I am running the coax away at a 90 degree angle. The
lighter/smaller coax is more suited for this arrangement. I didn't
use RG6 (which I actually have) because the reducers for the PL259
and ferrite beads I have don't fit this size coax. I figure for 3.8Mhz
that loss wasn't such a big issue...in addition to the 1/4WL section
of 75 ohm coax is only another 25 feet of 50 Ohm coax to the shack.

-Scott, WU2X



On Aug 21, 1:15 am, Owen Duffy wrote:
" wrote groups.com:



I use RG6 quite a bit for ham work, and the cable I buy uses a HDC
centre conductor. I would avoid CCS for lower HF.

For what it's worth, I looked up the specs on the Carol C5785 that is
locally available at Home Depot here in the States. It's quad-shield
RG-6 and they list the losses down to 1MHz

1MHz .26dB/100ft
10MHz .81dB/100ft
50MHz 1.46dB/100ft

According to your calculator for RG-6/U it should be
.19
.6
1.37

Dan, You didn't say which of the RG6 cables you used. The figures you
quote are very similar to Belden 1189A. In respect of 1189A, note that
the regression model is based on data points from 55MHz to 1000MHz. That
is either because that is what Belden supplied, or it could be that I
excised some low frequency data points that were a bad fit to the model.

Beware of results where the estimate is an extrapolation. (The frequency
range is red when the estimate is an extraplation.)

Owen

How much can the impedance of coax vary from its characteristic impedance?
 

wrote in message
oups.com...
The RG-59/U I am using does in fact have a stranded center conductor.
I am using RG-59/U because I am feeding a vertical (quad) loop on the
vertical side and I am running the coax away at a 90 degree angle. The
lighter/smaller coax is more suited for this arrangement. I didn't
use RG6 (which I actually have) because the reducers for the PL259
and ferrite beads I have don't fit this size coax. I figure for 3.8Mhz
that loss wasn't such a big issue...in addition to the 1/4WL section
of 75 ohm coax is only another 25 feet of 50 Ohm coax to the shack.

-Scott, WU2X


You might also want to take a look at feeding one of the bottom corners.
This will give both vertical and horizontal polarization. I found it worked
great for DX; a dog for working locals, but probably no worse than vertical
p. I subsequently added a 1:1 current balun, but don't think it did anything
relative to the original setup, which had the center conductor connected to
the vertical wire.

Tam/WB2TT