At 04:19 PM 05/26/07, you wrote: >One other thought... > >If they don't already have dtmf mics on their radio gear then I >would not consider adding them for cost and reliability reasons. > >I'd probably buy some of the low cost key-chain remote control >units and the master decoder receiver. > >It's probably easier to buy a $10 to $25 key-chain remote vs. having >to place new dtmf mics on radios. > >skipp
And one more bonus - if someone loses the key-chain remote or if someone gets fired and keeps theirs it can be "dropped" from the master a lot easier than reprogramming a DTMF decoder and informing everyone of the new code. There's always someone that doesn't get the message... And one comment on using a garage door opener... as I remember the starting message to this thread, it's a tower site company. This means high altitude... and the garage door opener receiver will be able to "see" a lot of residential area... what;s to say that some consumer down in the valley won't have the same RF frequency and digital code on their opener? There are openers that have a "rolling code" feature, but I don't know if those units can handle multiple remotes controlling a receiver at each of multiple sites. And all of the above assumes that the garage door opener receiver even survives at a tower site that has lots of RF in the air... (and I'm not kidding - I've seen a Genie brand receiver in a metal box with SuperFlex going to a pass cavity with 3db loops... with a 6db pad on the cavity output... and a RG-8-sized feedline to a coathanger-style ground plane. I was not able to get close enough to the feedline to read the cable type). If you do go with DTMF mics on all the mobiles (are they in place now?) and an appropriate decoder on a commercial receiver on the talkaround channel I'd suggest a deliberately poor antenna. Maybe a 6 or 10db pad between the RF connector and a stubby duck. Just to keep the riff-raff out of the system. No sense in allowing someone thirty miles away who has a beam antenna and a DC-to-Daylight programmable radio be able to open the gate. But I still question broadcasting a DTMF sequence over an open radio channel. Anybody can listen, anybody can decode, anybody can duplicate the signal. If I remember the original message there are power gate openers... a good quality key switch accessible from the vehicle door would seem to scratch their itch. Sometimes low tech is more secure. Use a Medeco or Abloy if you need key blank control. If not, just pin the key switch to an existing key on the company vehicle keyring. I know of one site where the padlock on the gate is a Schlage, and the keycode is the same as the shop vehicle driveway gate. Another trick... pick a community repeater frequency at the site... put the insensitive commercial radio on that input. Program the receiver for a DPL code that no existing user currently has. Have the DPL decoder drive a relay to open the gate. Or if the DTMF mics already exist have the DPL decoder enable the DTMF decoder. Mike WA6ILQ
