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Service Providers >> Satellite Internet - Middle East >> Coax connector 50ohm v. 75ohm C band https://www.satsig.net/cgi-bin/yabb/YaBB.pl?num=1275193479 Message started by satnew on May 30th, 2010 at 5:24am |
Title: Coax connector 50ohm v. 75ohm C band Post by satnew on May 30th, 2010 at 5:24am
Please help..
what would be the effect on RF measurements when using a cable assembly with 50ohm connector and a 75ohm connector on the other end using a 75ohm coax cable. Further to this, can I just use a 50ohm cable assembly for all RF measurements? note: RF is C-band.. tnx |
Title: Re: connector Post by Eric Johnston on May 30th, 2010 at 11:27am
Ideally you need the same source and load impedences as well as connectors and cable type.
If you have a mixture, the effect is partially reflected signals which results in amplitude ripple due to partial signal cancellations/additions across the frequency band. This will add errors to measurement accuracy - but it depends what you are trying to measure or observe - if you are simply looking to see a particular small carrier on a spectrum analyser then maybe the ripple errors and absolute levels don't matter. The partial reflections also cause mulitpath delay effects, like shadow images on analogue TV and inter-symbol interference in digital systems. Similarly don't crush coax cables at regular intervals (e.g. using wall clips, clamps or cable ties). If you are connecting a C band BUC with a coax output via coax to the feed OMT you should must use 50 ohm Andrew Heliax cable (or similar) and Andrew 50 ohm N type connectors at both ends. Be aware that 50 ohm N type and 75 ohm N type plugs exist. Never put a 75 ohm N type plug to a 50 ohm N type socket - the centre pin won't connect properly as the 75 ohm centre pin is very slightly smaller diameter. I agree with the desirability of using 50 ohm for all C band RF measurements. Best regards, Eric. |
Title: Re: Coax connector 50ohm v. 75ohm C band Post by Oasis Networks on May 31st, 2010 at 2:04pm
Just another small note -
Impedence mismatch might lead (it depends on the signal frequency and cable length) to a specific phenomenom of standing waves, that might lead after several years to cable break. This is as a result of hitting at certain points along the cable that after some time will lead to cable break. I think I still have this article somewhere if more detailed explanation is required. |
Title: Re: Coax connector 50ohm v. 75ohm C band Post by satnew on Jun 2nd, 2010 at 5:12am
Thanks Eric..
Hi Oasis, will appreciate if you could send me the link of the article you mentioned. Thnkx and regards |
Title: Re: Coax connector 50ohm v. 75ohm C band Post by Oasis Networks on Jun 2nd, 2010 at 8:48am
Hello,
I have it printed and I can scan and send by email. Please contact me privatly and provide me with you email address and I will mail it to you. Kind Regards, Nimrod |
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