Acceptable resistance through plugs??

[TuffRR]

I have an external GPS antenna which i have put a plug in the cable. The RF cable is RG174/U and i am using a suitable male and female connector from RS Parts. With the external aerial plugged in i cannot pick up any satellites but i can with the std Garmin antenna so something is not working with the external antenna.

I have got my multimeter onto it and on both parts of the cable (it is now in two seperated by the plug) there is no resistance from one end to the other. However when i join them up the multimeter reads between 540 and 1100 when measuring resistance. I have identified this resistance to be exactly where the connector is.

I'm kinda learning all about electrickery so am not sure if this is a normal reading for using a connector as i understand some loss may be normal.

Any advice?

TIA.

[gqswb]

Did you crimp the plugs or solder, Those SMA style plugs can be a real pain sometimes. There should be no resistance at all, if you say that there is a high resistance when the cables are joined maybe they are not interfacing corectly. No one can realy fix over the net. Just get back to work and FIX IT! hehe goodluck.

[TuffRR]

I soldered the cable into the connector pins and these have a good connection because there is no resistance with these individually.
As you said, the resistance is between the male and female pins interfacing. Seems odd as they both look brass and should connect well.
Your post seemed to suggest this is a common problem?

BTW, these are the type of connectors i am using....

http://www.rsaustralia.com/cgi-bin/bv/s ... aunetscape

[gqswb]

"For security reasons your session has timed out"

Whats the part number? I'll do a search on there site. On the plug you soldered did you push the pin in until you heard a slight click? is it in as far as it will go? if there is any solder on the side of the pin they usually won't fit all the way.

[Tas_Dean]

Check the resistance between the inner core and the outer cover of the connector. This should be extremely high. If not it means that you have a wire shorting out (can be just a single strand) and this will negate the effects of the external antenna.
If this is the case you will need to pull the whole lot apart and start again, being very very careful!

Is this reading you are getting from the same part at both ends (ie sheath to sheath or centre to centre?)

If it is definately the connectors, try some fine emery cloth/wet and dry to clean the connectors up!

[TuffRR]

Check the resistance between the inner core and the outer cover of the connector. This should be extremely high. If not it means that you have a wire shorting out (can be just a single strand) and this will negate the effects of the external antenna.

You may be onto something, one of the plugs has high resitance but the other has none between the inner pin and the outer case. I will redo this plug and hopefully this will solve the problem.

[Tas_Dean]

You may be onto something, one of the plugs has high resitance but the other has none between the inner pin and the outer case. I will redo this plug and hopefully this will solve the problem.

If you are reading this at one end of the cable and not the other, this means also that there is no connection to one end of the cable on at least one of the cores.

The correct testing procedure for any cable like this (including CB or UHF bases) is to test (using the resistance scale on a meter) between the inner cores at both ends (should be a very low reading, preferably 0-2ohms, test between both outer cores of the cable (also close to 0ohms), and then test between the inner and outer cores at both ends of the cable (should be extremely high, however capacitance will create a reading that slowly gets lower!)

Hope this helps,

Dean

[TuffRR]

Good stuff Dean, it all makes sense now.

[Woop]

Some GPS Antennas are active types as well--ie powered.

Nick