At 5/8/2009 21:26, you wrote: >A Home Brew 224 MHz Repeater Project. >May 2009 >Part 3 The exciter (transmitter) >First Post May 2, 2009, Second Post May 6, 2009 - This Post May 8, 2009 > >Moving right along...
(snip) >Let's talk about the coax connector being an RCA jack on the >exciter PC Board. Why bother with a box chassis mount connector >added to the path Why? To maintain proper shielding. Again, passing a wire/shield/any conductor through a hole in the box without bonding at that point will make the conductor act like a coupling probe. Sure, it may work but I claim so would doing away with the box altogether, so you could simply bolt the exciter board to a plate. Of course the harmonics generated by the exciter will radiate. If there are any RXs at the site that are harmonically related to your 220 TX you'll probably find out about it. I once had a similar problem in reverse (440 MVP hitting a co-located 220 RX exactly 1/2 the MVP TX freq.). This is where I learned about effective shielding techniques, & why you can't do what you outline below. > when in many cases it's more loss than it's >worth. So... I soldered an RCA connector on the end of a section >of quality small size (brown tan) Teflon coax and routed it >through a hole made just large enough (to pass the RCA plug) with >a Unibit Step Drill (bit). A low cost clone set (three in one >package) of Unibit type step drill bits are almost a must have >expense of less than $15 at Harbor Freight. > (snip) >The disadvantage of leaving the oscillator on all the time is a >constant "local" low level signal that is sometimes a lot stronger >than you would expect. One of my 224 MHz Spectrum transmitter >oscillators can be heard almost a half mile from the repeater >site (which is not really very professional or something to be >proud of). > >In the case of this model exciter, one can key the entire module each >transmission knowing the synthesizer requires about 350 mS (Milli >seconds) to come on the air. Yuk! Wonder if there's some way of leaving the synth. powered up while disabling the rest of the exciter so you don't have to deal with this delay yet still not have the TX signal heard near the site. Bob NO6B
