Or all my builds, i have used SMA extension leads between the VtX, not only so i can put the antenna where i want, but also for "strain relief" purposes.
My last build was A WOT4 where i used a 12" cable, but due to the "spars" in the fuselage, could only get the antenna 6" back but as it was hollow was able to "bundle" the slack inside. But it was also a night,are trying to thread a connector through.
My new build has a solid body which means hiding the slack will be difficult but also getting a connector through 12" of foam might be tricky..
But i wondered if i was missing the obvious. Could i just cut the end of my extension cable off.. Thread the thin coax through and then solder a panel mount connector on such as this?
http://www.ebay.co.uk/itm/290549180595?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649 (http://www.ebay.co.uk/itm/290549180595?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649)
I am sure it will be ok as the connector and cables are the correct impedance. But i have to be honest, even though i am an electronics (now software) engineer by trade, the RF and "impedance" was never really my strong point..
So are there any radio people here who could confirm that this will be OK?
Jon
Jon,
You'll be 'almost' fine with that however there looks to be one problem with it.
When you connect the coax to it the centre pin will be fine, the outer braided screen on the coax is another matter though as ideally it needs to be continuous all the way to the connector body (especially if on 5.8) which in turn gets continued on to the aerial SMA connector.
The fitting you've linked to is reliant on being bolted to a metal panel or ground plane, the pictures don't show any crimping ferrule (tube) coming with it, so you need to do a bit of work to get the outer coax braided screen to run onto the back of the fitting then solder it to it, all a bit fussy.
Much better would be to do it with an SMA straight crimp connector, crimp that on and connect your antenna as usual..... only thing it doesn't give you that nice bulkhead type fitting to fix to the fuselage nice and neat :)
If It was me and I needed the bulkhead type fixing I'd do it with the fitting you've shown and try making a small metal plate to use on the back drilled out to match the fittings bolt holes, drill the centre hole big enough to let the thickness of the screen braid through, spread it out and then clamp it all up..... if you see what I mean :)
Also a couple of lengths of heatshrink and some epoxy around (or a short length of suitable dia tube) to give it some strength as just the coax to the white nylon part of the fitting isn't giving much mechanical strength.
Hope that helps
PK :)
Quote from: pk-surfing on August 23, 2014, 03:18:56 PM
Jon,
You'll be 'almost' fine with that however there looks to be one problem with it.
When you connect the coax to it the centre pin will be fine, the outer braided screen on the coax is another matter though as ideally it needs to be continuous all the way to the connector body (especially if on 5.8) which in turn gets continued on to the aerial SMA connector.
The fitting you've linked to is reliant on being bolted to a metal panel or ground plane, the pictures don't show any crimping ferrule (tube) coming with it, so you need to do a bit of work to get the outer coax braided screen to run onto the back of the fitting then solder it to it, all a bit
PK :)
That part of the question, i am ok with as thats "electrical". I was more concerned about the RF/Impedance aspect.
In the case of the bulkhead connector i linked, my assumption is that there would be a way to solder the braid to the "chassis". If not, i would simply find a way to do just that. With a decent iron, it should be possible to solder the braid to the bulkhead at the back of the connector..
A crimp connector would obviously be better..but its getting hold of the specific tool i might struggle with which is why i figured solder would be better.
For peace of mind you could do an SWR test of it once completed, using the extension cable/antenna combination together for the test, if it gives a decent SWR then no problem.
Crimping is the usual method for coax onto connectors but the bulkhead fitting looks to have a white nylon collar so that's no good to crimp onto, go with your solder option and it will work fine.
PK :)
Quote from: pk-surfing on August 24, 2014, 07:56:48 AM
For peace of mind you could do an SWR test of it once completed, using the extension cable/antenna combination together for the test, if it gives a decent SWR then no problem.
Crimping is the usual method for coax onto connectors but the bulkhead fitting looks to have a white nylon collar so that's no good to crimp onto, go with your solder option and it will work fine.
PK :)
Exactly.. I would typcially crimp any RF connector, but since this is sold as a "solder" connector i assumed it was just that.
To be honest, i could easily get cables made up (or get hold of a tool). Not only do i work in telecom, but i have a contact in work who is a HAM. And also a friend who makes antennas for the MOD. But i dont like being dependant on them and would much rather be able to make up a bulkhead connector at the exact length i want.
But to be honest, its possible that the fuselage on my new plane is hollow after all and i may be able to "loose" some of the cable and leave my extension cable intact. I wont know until i start cutting....
Cheers