Reducing length of GPS coaxe cable

You may find that the GPS needs all that cable due to it's impedance. Altering the cable length on my log and echo sounder transducers alters the signal, so when I fitted my GPS, I coiled up the co-ax for that too.
 
You can almost certainly get rid of the excess coax on your GPS. The only problem is making a satisfactory join. The best way would be to cut it to length and put a new plug on the end to go into the back of the GPS itself. The problem is that the various makers of GPS use some obscure plugs on their cabling.

When I fitted our GPS I unsoldered the cable in the antenna end and resoldered the connection after reeving the cable through the various conduits and deck gland. It helps that I was once an electronics engineer.

What make GPS?
 
The echosounder is transmitting (the 'pings') to a tuned circuit which includes the cable, so it cannot be altered without detuning. GPS and all the rest of your instruments are just "listening" to the tranducer/aerial so you can cut the cable and join without penalty as long as it's done properly, which is not rocket science.
 
As others have said, it is perfectly do-able with a GPS and the real issue is getting the connector back on reliably. Many modern connectors are put on with special machinery and this produces a highly reliable "gas-tight" join that is superior to soldering. Not all such connectors are available in solder form. With Raymarine cables (HSB - not HSB2 and SeaTalk) I have got round this by cutting off the connector with a good tail and re-make the join in the cable. If you are careful you can solder the individual wires together, insulate with ordinary PVC, take the screen across and then finish with self amalgamating tape.

I then tuck a loop in, held in place by a cable tie to prevent any strain falling on the connection. The loop doesn't look tidy but it is very functional and I hide them in any case. I understand that HSB2 is much faster than HSB(1) but the latter is fine my way and I guess that HSB2 would be, too.
 
[ QUOTE ]
As others have said, it is perfectly do-able with a GPS and the real issue is getting the connector back on reliably. Many modern connectors are put on with special machinery and this produces a highly reliable "gas-tight" join that is superior to soldering. Not all such connectors are available in solder form. With Raymarine cables (HSB - not HSB2 and SeaTalk) I have got round this by cutting off the connector with a good tail and re-make the join in the cable. If you are careful you can solder the individual wires together, insulate with ordinary PVC, take the screen across and then finish with self amalgamating tape.


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The join will not be the correct impedance using this method.
 
[ QUOTE ]
The join will not be the correct impedance using this method.

[/ QUOTE ] You are talking about the characteristic impedance, Z0? You'd be surprised how good it is. I used this method back in the days when I was an RF engineer working on antenna design, for a while, and had all the kit in the world (courtesy of the MOD) to check VSWR, and could produce Smith charts in a few seconds (which was very high tech in the '70s!). Done with care, and being sensitive to the overall objective of trying to make the join as much like the original cable as possible, the discontinuity appears small - much less than 1.2:1 is possible.

In any case, that isn't relevant for the GPS (the OP's question) as the frequencies are very low. It might be relevant for the HSBs - indeed, I was told by a Raymarine technician that it wouldn't work - but it does work for HSB but, as I said, I haven't tried HSB2 but I bet it's OK.

Of course, this is a different problem to depth sounders where the capacitance of the line is part of the tuning of the piezzo transducer so if you shorten the line you need to pad it with some extra C.
 
Well it won't be perfect but it will work. And, interestingly, 'coiling it up in the wheel house' will alter the impedance a lot more!
 
GPS is 1.6 GHz so not low freq. There is also a DC feed to the antenna via the coax so connector needs making carefully

That said, the length isn't critical until it gets over about 10m (depending on the type of coax) when losses start to seriously attenuate the signal. Cutting off the excess won't make any difference at all
 
Yes, I may have misread the question a bit though it doesn't affect the suggested action.

If the antenna is purely an active antenna without any processing then the signal will be almost 1.6GHz but if it is a Raymarine-type head then the processing is carried out in the head and all it gives out is SeaTalk (and also NMEA?) which are low frequency. The attenuation at 1.6GHz is fairly high per meter even with pretty decent coax and the losses in the cable will quickly be greater than the loss due to the VSWR. I haven't got any cable tables to hand to quantify it.
 
The OP is talking about telly type connectors so assume it's coax. If so then it's prob an active antenna not a complete gps receiver which wouldn't use coax at all
 
Yes, you're right. He won't have any probs doing what he wants to do as it is much easier to make the connection on a coax in any case.
 
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