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Coaxial Cable Q factor. - RF Cafe Forums
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Simpang
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Post subject: Coaxial Cable Q factor.
Posted: Fri Apr 11, 2008 2:42 am
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Joined: Fri Apr 11, 2008
2:11 am Posts: 3 |
Can anybody recommand which type of coaxial cable
to use to meet the following specification.
The length of cable : 2.85 meter. OD of
cable : 5.0mm +/- 0.3mm Capacitance : 150pF
+/-10pF Q factor : More than 200 @ 1Mhz
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nubbage |
Post subject:
Posted: Mon Apr 14, 2008 11:03 am
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General |
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Joined: Fri Feb 17, 2006
12:07 pm Posts: 218 Location: London UK
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Hi Simpang There are RF coaxial cables that
meet some of the parameters, but not others.
I feel the capacitance per m figure is too high
for a cable with 5mm OD. If you look at RG83
or RG88 they are bigger OD but have this high value
of capacitance you specify. I have used a mineral
insulated fire-rated instrument cable as an antenna
feeder in high temperature fire/safety applications.
This met the 5mm OD constraint and came close to
the capacitance per m figure of 150pF. However
this is not intended for RF use, but because you
only need a short length this might be OK. It
was a Pyotenax single core inner (approx 0.8mm diameter)
solid soft copper outer but I do not know the part
number. The filling permittivity was around 5, the
outer diameter was 5mm and the capacitance about
146pF/m
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Simpang |
Post subject:
Posted: Tue Apr 15, 2008 2:18 am
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Joined: Fri Apr 11, 2008
2:11 am Posts: 3 |
Hi Nubbage
Thanks for the advice.
The capacitance of 150pF is the total capacitance
of 2.85 meter length og cable. This work out to
be 52.6pF per meter length of cable.
The
q-factor of more than 200 is also refer to the 2.85
meter length of cable.
Will appreciate very
much if you can recommand again.
Thanks
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nubbage |
Post subject:
Posted: Tue Apr 15, 2008 4:41 am
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General |
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Joined: Fri Feb 17, 2006
12:07 pm Posts: 218 Location: London UK
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Hi Simpang It seems it would need to be a 75
ohm characteristic impedance cable. The nearest
to the spec you give is RG6, Belden 46462, Taylor
H109 or Volex-Raydex CT100. This has a diameter
over the braid outer of 5.15mm, and a capacitance
of 56pF/m which would give a total capacitance of
160pF. The Q is easy to meet for all of those
cables at VHF/UHF
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Simpang |
Post subject:
Posted: Wed Apr 16, 2008 12:44 am
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Joined: Fri Apr 11, 2008
2:11 am Posts: 3 |
Hi Nubbage,
Thanks. have a nice day.
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Posted 11/12/2012
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