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Topic: I hate RF ! (Read 1 time) previous topic - next topic

Boffin1

Even when I was a radio ham in the 60s, I hated RF.  I couldnt see it, and at 10watts on top band -  I couldnt feel it.

I could work out the exact length for an antenna, but then found you have to trim it afterwards !  I much preferred logic circuits, all true false and no maybes.

Some time later I worked on the Boeing 707, which had a horizontal whip that stuck out horizontally from the top of the tail, but was found to emit vertically polarised signals  !       I hate RF.

50 odd years later, I am using 433 MHz links in many projects.  I came up by accident with a fantastic whip antenna for the remotes, with which I get good range, and they cost the price of a BNC plug, plus 160mm of curtain expander wire, with a rubber bit on the end to save peoples eyes ..  It looks cool and can't be easily damaged.

At the receive end, I usually just have a 160mm or whatever length of wire behind a plastic LED display.

Now I have made some units that have the transmitter in a box behind the display, and I am assuming that the front of the display board will be Chromadek ( metal ) so I am fitting the antenna inside the display , and want to run a 1m length of RG174 coax to the transmitter behind.

The shield of the coax will be grounded at the TX end, but for the life of me I can't remember what to do at the antenna end in the display.
I can just let the centre wire stick out for 160mm,  or I could ground the shielding on some metal at that end.

Of course I can try it and see, but if there is a preferred method I would appreciate having my memory jogged  !


kg4wsv

depends on how much metal there is at the antenna mounting point.

If it's a metal box that is a significant portion on 1/4 wave, ground the coax on the box and use the box for your ground plane.  If you have much power, this could be unpleasant for the electronics inside. :|

-j

Boffin1

Thanks Guys,

I am only receiving, so there is no power this end, so perhaps I will use the case as a groundplane then ( I line half the plastic box of the remote with foil as a groundplane and it seems to work )

Telecommando, I am going to run out of box if I go 300mm high with a dipole, but thanks for the suggestion, its all bringing it back to me now ( I still hate RF !!! )

ex  G3STX


AWOL

433MHz would be closer to 17cm than 16cm, wouldn't it?
( 299,792,458 / 433x106) / 4 = 0.173 metres.
(I hate RF too)
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

Boffin1

Quote
433MHz would be closer to 17cm than 16cm, wouldn't it?


Yes, I havnt measured it for a long time, I just chop it to the same length as a commercial one I keep handy   ( I suppose I had better measure it in case I lose it :-) )

Boffin1

Incidentaly,  I hate RF, but need to use it for my projects.

In the same way,  I hate Facebook, but have to use it to keep in touch with all the grandchildren !

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