Are we missing the obvious here?? Are all of the mobile radios capable of sending 1+1 or MDC type signaling?? I would think MDC especially would be more secure than either DTMF or PL type stuff. Even if you had to buy a small cheap voice recorder and play it back though the microphone manually... (Similar to the old pocket phone dialers)
I know maxtracs can be had for little money that when paged with activate the horn/light relay output on the back. I would think that could be used to help keep things more secure. I think they can also be programmed so that they must have the correct PL/DPL code along with the 1+1 to make it trip. Just an idea. YMMV Scott Scott Zimmerman Amateur Radio Call N3XCC 612 Barnett Rd Boswell, PA 15531 ----- Original Message ----- From: "Mike Morris WA6ILQ" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Saturday, May 26, 2007 7:25 PM Subject: Re: [Repeater-Builder] Re: OT: Need to find a product to develop goodwill at a tower site(s) > 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 > > > > > > > Yahoo! Groups Links > > > > > > -- > No virus found in this incoming message. > Checked by AVG Free Edition. > Version: 7.5.472 / Virus Database: 269.8.3/824 - Release Date: 5/29/2007 > 1:01 PM > >
