At 5/24/2009 21:57, you wrote: > > >A Home Brew 224 MHz Repeater Project. > > >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 > > > n...@... wrote: > > Why? To maintain proper shielding. > >No, to eliminate the extra loss of two additional jacks >and plugs. Since the exciter output is down near the >trailing amplifier's practical minimum drive level (value), >it's nice to where possible reduce unwanted signal loss.
OK. But if you really wanted to minimize the loss between the exciter & PA, you could use an N bulkhead (virtually lossless @ 220 MHz) so you could use some larger diameter coax between the box & PA, or even Superflex. > > 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. > >I tried and measured at least three different construction >techniques... all had the same results. The first was >just holes in the box, no bonding to the metal box. Keep >in mind the actual length of coax (inside the box) routed >to the exciter RCA Jack you assume is an RF probe is >really short. OK, that's probably why you don't get much coupling to the outside of the coax. At 440 (where I normally work) & higher frequencies, it's much harder to keep those distances short enough to avoid problems. >I did a lot of "RF looking around" the exciter, at pc board >level, near the board, in the box with the board running, >box cover off and box cover on. Credit to the latest version >of the Hamtronics T-301-6 Exciter for being well thought >out in regards to RF shielding and having very minimal unwanted >RF products both near-field (radiated) and out the coax port. Is the synthesized output the fundamental signal, or is there multiplication after the oscillator? If it's the former & they're using a clean oscillator, there may be little harmonic content generated on the board. Bob NO6B
