Another tip from the UK, is to paint the antenna(s) with Marine varnish several times, this prolongs their durability and certainly stops any rain or otherwise penetrating the fiberglass tube(s) over time. Might look ugly, but an ugly working antenna is better than a non working 'clean' one!
73 Neil G7EBY. On Apr 20, 2010, at 5:43 PM, Daniel G. Thompson wrote: > Bob is definately correct that the typical 4 can setup used > on the average FM repeater will cause you nothing but > headaches, and that includes the ultra nice TX/RX stuff. > You either have to go with a 6 can setup using pass/reject > or like Bob said, throw an DCI filter between the > duplexer and receiver. This is also true of the VHF as well. > We fought with this problem for a couple of weeks before we > went on the multiplexer with about 40' between the antennas. > The "traditional 4-can setup" often doesn't work well with Analog systems either, but the owners are too clueless to test it and see. :-) Most 4-can setups also really need a large hi-Q pass cavity on the Receive side to reject out of band and close-in crapola at multiple-transmitter sites. > Bottom line I think for this thread, is repeaters are fussy when > it comes to a good feedline and antenna system, and D-Star > is even fussier. On D-STAR it's just damn hard to test it properly. So you do the pants+suspenders thing and over-filter it a bit. The receivers are more sensitive than what most analog repeater operators are used to working with (60's vintage through 80's vintage receivers that had nice tight front-end filtering built in, vs. a badly shielded aluminum box that blocks nothing, bad quality coax internally -- which can be fixed -- and a really sensitive but not very SELECTIVE receiver... inside the "pretty" D-STAR aluminum box). I'll take the front-end helicals of a MASTR II any day of the week -- even the loss! -- over the Icom RF design that looks like it was built out of two mobiles in a box... oh wait, it was... One was ENGINEERED, the other one was ASSEMBLED. There's a big difference between those two schools of thought. One doesn't require a school at all, in fact. ;-) Again I'll rant lightly that without real numbers for when the CODEC itself falls apart (bit-error rate) and a way to test it... testing these things properly is an exercise in a whole lot of ASSUMPTIONS and trial-and-error style antenna/filter system design. Sharing real-world stories of what works and what doesn't, kinda fixes that, but it sure would have been easier if it wasn't left to the users of the repeaters to beta-test them for the manufacturer. A couple of models of "expensive as hell" Service Monitors can now record an off-air digital signal and then play it back, so you add attenuation and reverse-engineer any type of digital repeater, but expect to be in the $40K range for them, list. Probably $20-$25K real-world, pricing. Not something we're going to see too many hams doing, I suspect. -- Nate Duehr, WY0X [email protected] <mailto:nate%40natetech.com>
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