Visit RFCafe.com Thanks for visiting RFCafe.net Thanks for visiting the RF Cafe Archives Thank you for visiting RF Cafe Thank you for visiting the RF Cafe Archives!

Coaxial Cable Q factor. - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues - primarily having to spend time purging garbage posts from the board. At some point I might start the RF Cafe Forums again if the phpBB software gets better at filtering spam.

Below are the old forum threads, including responses to the original posts.

-- Amateur Radio
-- Anecdotes, Gripes & Humor
-- Antennas
-- CAE, CAD, & Software
-- Circuits & Components
-- Employment & Interviews
-- Miscellany
-- Swap Shop
-- Systems
-- Test & Measurement
-- Webmaster

Simpang
 Post subject: Coaxial Cable Q factor.
Posted: Fri Apr 11, 2008 2:42 am 
 
Lieutenant

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


 
   
 
nubbage
 Post subject:
Posted: Mon Apr 14, 2008 11:03 am 
 
General
User avatar

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218
Location: London UK
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


 
   
 
Simpang
 Post subject:
Posted: Tue Apr 15, 2008 2:18 am 
 
Lieutenant

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


 
   
 
nubbage
 Post subject:
Posted: Tue Apr 15, 2008 4:41 am 
 
General
User avatar

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218
Location: London UK
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


 
   
 
Simpang
 Post subject:
Posted: Wed Apr 16, 2008 12:44 am 
 
Lieutenant

Joined: Fri Apr 11, 2008 2:11 am
Posts: 3
Hi Nubbage,

Thanks. have a nice day.






Posted  11/12/2012
RF Stencils for Visio v3.1 by RF Cafe
RF Cascade Workbook 2018 (GS) - RF Cafe
About RF Cafe Archives
Kirt Blattenberger - RF Cafe Webmaster
Copyright: 1996 - 2024
Webmaster:
    Kirt Blattenberger,
    BSEE - KB3UON

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ...

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

My Hobby Website:  AirplanesAndRockets.com

spacer