At 5/7/2009 09:35, you wrote: > > > Don't panic, the TS-32 also provides a separate tone > > > generation "encoder" section for your transmitter CTCSS > > > requirement. A shielded audio quality wire is routed out > > > of the receiver box to the transmitter board at the > > > proper CTCSS connection point. > > > I assume this is done using feed-through capacitors - you > > don't want to plumb any wires straight through the case. > >In the past I've actually routed the shielded CTCSS endode >audio source wire through chassis and cabinet/box holes >and in this case I used the feed through-capacitor method. >The holes in the direct wired version was already there so >I used it. Through hole direct wiring can make servicing >by box swapping a bit more difficult. In very short wire >lengths I have not experienced a problem with stray RF or >Ground Loops bringing a gremlin on board.
Yes, but if you run a wire into a box through a hole, you might as well take the lid off too, as that wire will act just like a coupling probe between the boxes. Similar situation: I mistakenly used an isolated BNC feedthrough on a shielded box with feedthrough caps on all other I/O. Inside the box was a scanner being used as a sig. gen. The scanner's LO leaked out as if the lid was off the box because the BNC bulkhead was isolated. Replaced it with a standard BNC feedthrough & the signal went from FQ all over the room to no detectable leakage, at least a 60 dB change. > > >The Hamtronics Receiver COR/COS output is active high, which I > > >don't like one bit. > > > > When I first started building repeaters, I used active low > > CTCSS as well. Oops - that should have been "...I used active low COS as well." I also used active low CTCSS, but I still do today - that never changed because the RLC-1 controller only works with active low CTCSS. > The main reason was that it was convenient > > to use as a cheap way to key the TX when a controller wasn't > > available back in those "lean" college days. When I started > > using G.E. radios with their active high CAS & RUS outputs, > > I switched to active high as my standard. > >I like active low logic for a number of reasons and personal >preference. In a situation where the controlling device loses >power, there is a potential for the transmitter to key up. If the RX loses power, the logic outputs could pull to ground as well - depends on the design. In my case, using opposing polarities on COS & CTCSS appears to eliminate the possibility of both becoming spuriously valid. > > So what do you use for a connector? In my latest RX boxing > > project I decided to put a DB9 "doghouse" on the box. The > > doghouse is a cheap plastic box since shielding isn't necessary. > > I plan to install the feedthroughs in a manner similar to what > > you describe, but then mount a DB9 & Anderson PowerPole on the > > doghouse so all the connections are "connectorized". I may > > even add some switching circuitry inside the doghouse so this > > receiver can be grafted into a existing system using a > > single-port controller (2 RXs on one port). > >For this project... I only used the feed-through capacitors >for everything. The wires at the rear of the controller get >into the controller via a DB-9 plug but nothing on the chassis >or RF deck. I stopped using small Anderson Power Pole connectors >because of all the grief they caused me on the commercial >radio side of my life. A lot of people like and use them but >I don't trust or use them anymore after a few 10 hour days >sourced back to intermittent small power-pole connectors. Uh oh, I hope I don't run into that problem. I began to standardize on the PowerPole a few years ago & have about 80% of my equipment converted. Before that I direct-wired everything, but that just got too painful every time I needed to swap something out. For a short time I started using Molex but the current rating of the easily-obtainable versions was only 8 A - not enough even when doubled up. Up to now the only negative comments I've heard regarding the PowerPole are related to their non-locking nature. I've found their inherent retention force to be more than sufficient for all my applications, both repeater & mobile. I know that PowerPoles (& probably almost all other DC connectors) are NOT designed to be hot-mated, which could cause contact problems. Sometimes it's unavoidable, but I try to prevent it whenever I can. > > > >and while the value is not ultra critical, you don't > > >want the capacitance value large enough to impact the information > > >passing through. I found and used surplus 100pf (pico farad) > > >feed-through capacitors although I'm sure higher values will work. > > > To make sure that the shunt capacitance blocked any RF, I > > added some series resistance to form an RC. On lines like > > the RX audio, adding 470 ohms in series with a source that > > was already several k-ohms didn't affect the audio > > at all. Same for COS & CTCSS decode logic outputs if the > > controller's input impedance is much higher than the series > > resistance used. Also serves to protect those outputs if > > you accidentally short them to 12 V or ground. > >Unless I'm sure there's going to be a lot of shear RF at the >repeaters location... I take the simple and easy route. Even >with a broadcast station nearby (but not in the same value) >I didn't feel the advanced filtering techniques were required >and so far, so good. When I box a RX, it's usually because I'm having an interference problem due to insufficient shielding. So I want to be darn sure I don't have to do it again. Bob NO6B
