Shortening the GPS antenna cable

Reach Module / M+ / M2 Hardware integration
1

So I cut my Tallysman TW4721 antenna cable short to be able to fit it on a small quad.
It’s just a simple coaxial cable so I thought it should be fine if I just re-solder the two ends and insulate.
However, I am not able to get any satellites anymore, it looks broken :frowning:

Is there a trick to shortening the antenna cable?

Thanks

2

Hi Ivan,

There is no special trick, it is truly just a coax. Normally cable is shortened by cutting it and then crimping a new connector.

1 Like
3

I suppose it depends on your method. Did you try this:

  • peel back the outer shielding on both sides,
  • solder the core wires together,
  • insulate the core wire solder joint (maybe use the same insulating material that was on it),
  • then push the outer shielding back together and solder,
  • and then insulate the outer shielding.

Even doing it this way is not ideal. The spacing between the outer shield and the core determines the impedance of the cable, so if the spacing is messed up, then you have mismatched impedance and will have poor signal. You also get poor signal when you kink or crush the cable. Pretend it is the blood vessel going to your brain, and try not to damage it :wink:

GNSS signals are also very weak and you really need a high quality connection to keep the SNR values high, so that is why the right thing to do is attach a new connector to each end of the cut cable like @igor.vereninov suggested.

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4

Thank you for the detailed explanation. Even though I did everything like you said it looks like the quality of signal may suffer unless I use a new connector and a crimp tool.

What is the name of this particular connector @igor.vereninov?

Thanks

5

It is MCX https://docs.emlid.com/reach/mechanical-specs/

6

I have a similar question, could the cable be soldered directly to the pcb (after removing both mcx connectors) or would that alter the singnal characteristics/quality?

7

Hi @tobias-dahms,

We don’t recommend soldering the cable directly to PCB as it might affect the signal quality badly.

1 Like
8

Ok, thanks, I did fear that…

9

If you have not found already, you can buy ‘decent’ MCX coax connectors on ebay or aliExpress as well.

Generally a bag of 10 for $2-5 from china. Just make sure you get the correct gender and polarity.

You can also in theory get a few more opposite-gender connectors and keep the piece you cut-off as an extension cable…

1 Like
10

Thank you, I wonder if I need the appropriate tool too and where to get that?