tuning RFI CD50/51 antenna

[shmick82 Junior Member Find all posts View Profile Close shmick82]

Hi,

Anyone know how to tune the antenna? Ie cut it for desired frequency?
I've linked the instructions here:
http://www.rfiwireless.com.au/media/...cd51_68_70.pdf
but im not sure if they say to take the whip out of mount and cut from the bottom, or cut it from the top.
If cutting it from top, does the little cap just screw off?
Confused.

Mick

[shmick82 Junior Member Find all posts View Profile Close shmick82]

I think I solved it (im an amateur at this FYI)
Correct me if I'm wrong:
The RG58 cable is what goes from the unit (CB) into the antenna base, so the first part of the instruction is just terminating that (which installer already done).
So to "tune" the antenna, ie get it to UHF frequency, I cut it at 237 mm, from bottom, which will give me around 476-477 mhz.
Correct?

[Ian Reid Advanced Member Find all posts View Profile Close Ian Reid]

Yes you are correct


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[LeighW Avid PP Poster! Find all posts View Profile Close LeighW]

Would be better to use a SWR meter and tune antenna to the center of the band.

[shmick82 Junior Member Find all posts View Profile Close shmick82]

Thank guys.
What trade person would I look for to tune it? Auto elec?
Would it be fine without a tune?
Mick

[Ian Reid Advanced Member Find all posts View Profile Close Ian Reid]

Thank guys.
What trade person would I look for to tune it? Auto elec?
Would it be fine without a tune?
Mick

If you want it tuned take it to a radio communications place, Most auto elecs know SFA about RF comms.
If you cut it off the chart it will normally work ok, tuning with an SWR meter might gain you another percent or two but you probably wont notice the difference


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[LeighW Avid PP Poster! Find all posts View Profile Close LeighW]

There is two reasons you tune the antenna, one is to get the most power from it the
other is to keep the voltage on the output transistors within safe limits, hence why
they say don't transmit without an antenna connected. The radio should have some
form of output protection but judging by the high number of failures of the output
modules in some CB radios it would appear its not very effective.

If the antenna manufacture provides detailed info on the exact length to cut it to
then it should suffice, if they recommend tuning with an SWR meter then as Ian
wrote seek out a communications company or you could try one of the car radio
mobs or even a car spare parts mob such as Supercheap or Autobarn who install
CB's etc. Ask nicely if they have an SWR meter and know how to use it.

[shmick82 Junior Member Find all posts View Profile Close shmick82]

Thank you all very much for the info.