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What RF test cable should I use for network analyzer with SMA connector?

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jayleung

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Hi, everyone. I have a question about the RF test cable. I am going to make a prototype of an antenna. The test device is the network analyzer with SMA connector.

I am wondering what type (model) of the RF test cable I can use.

The prefer cable should have one end with SMA connector, and the other end with bald end, which means that the inner conductor of cable can be extended out to be soldered on the antenna feed, and the outer conductor can be soldered to the PCB ground.

Any reference will be appreciated. Thanks.
 

FANT

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Re: RF test cable

It depends on many things, but mainly on the frequency.
If the frequency is lower than 1 GHz you can use a RG142 cable, after 1 GHz use a semirigid cable as UT141.
Anyway to make this for frequencies higher than 1 GHz depends on many other parameters, as the exposed lenght, soldering, flux, etc.

Mandi
 

    jayleung

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jayleung

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RF test cable

Hi, Mandi. My project is working under 3GHz. And the cable should be easy to bend. The inner conductor exposed length is not quite long. I just want to solder the inner conductor to the feed of the antenna. So do you have any recommendation of the cables? Thanks very much for your help.
 

sergio mariotti

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Re: RF test cable

common RG, double braided coax cables may be used up to 5 GHz.
Phase and level stability are not excellent, but often good enough.
For istance, RG142 (PTFE) or RG223 (PE) are easy to connect, cheap, and lightweight solution.
Also their velocity is well kown so You can extend the VNA port along the cable.
 

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Samurai_Neophite

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RF test cable

I'm pretty sure a TRL calibration could be done here out to the end of your feed cable. You could use both methods. You can add in delay directly to the network analyzer to rotate the impedance into the proper place, which would negate the affects of your feed cable.

I'm a little rusty and haven't done this for 15 years, so I may have made a mistake.
 

    jayleung

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SagSag

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Re: RF test cable

you can use any cable you have as long as you calibrate you VNA with it.
I think the best cable is RG142, but you can use also RG55, if the cable needed is short use a semi-rigid.
 

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jayleung

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RF test cable

Thanks for all your guys reply. Here are some of my questions about the cable:

1. So where can I make an order for the RG 142 cable? I only need several pieces of 1' cables, and my budget is tight...

2. Are they already connected to the SMA connector?

3. If not, what type of the SMA connector should I used?

4. What kind of tool should I use to attach the SMA connector to the cables?

Thanks in advance
 

Samurai_Neophite

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RF test cable

Jayleung, I don't know if you're a student or a business or where you live, but as a student you could likely get a vendor/company to donate your cable requirements and get connectors. They may even possibly install them too. Installation can be a very strong learning experience as well!
 

    jayleung

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jayleung

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RF test cable

Hi, Samurai. Yes, I am a student in US. Actually I have installed SMA connectors to the cable before following my fellows in our lab.

However, since right now that guy have graduated, I don't know where he ordered that kind of cable.

Actually the cable I used before has no copper braid but solid as outside surrounding conductor. And I just need to use a small knife to cut a portion of outer shield copper and isolator out and solder the SMA connector on it.

And since all the RG type cable are braid type, I really don't know what kind of cable it is.

If someone is doing the antenna prototype before, please help.
 

Samurai_Neophite

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RF test cable

Well, now your an engineer. A big part of it is hunting parts. It takes a lot of time...... Google cables. If you want semi rigid, then there are companies out there. The rep will help you get what you want. I bet if you called the local Agilent representative, they'd tell you who to call or give you cable. Ask a professor for a local rep! Go to rfglobalnet or rfcafe.
 

    jayleung

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Samurai_Neophite

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RF test cable

Jayleung, thank you for the "helped" button pushes, I can't seem to be able to find that button when I want to push it for people. Can you tell me where it is located? Is it the donations button?

Thanks

Added after 3 hours 9 minutes:

found it. I didn't create the posts, so I couldn't see the button.

If someone helped you, use this button for send automatic thanks message and add 3 points (from edaboard.com bank) for selected helpful member.

This button is viewable only for person who created topic and can be used only one per helpful message. This is a great way for thanks - only one click. Special rank with the most helpful members will be created soon.
 

jayleung

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RF test cable

Hi, Samurai_Neophite. Right, I just press the "helped me" bottom for your information.

Finally, I find that I should not just use "coaxial cable" to search, but "semi-rigid cable" with your reminds~
 

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