At 06:41 PM 9/15/04, "Jamey Wright" <[EMAIL PROTECTED]> wrote:
>-----Original Message----- >From: Mike WA6ILQ [mailto:[EMAIL PROTECTED] >Sent: Tuesday, September 14, 2004 10:32 PM >To: [email protected] >Subject: Re: [Repeater-Builder] Voters > >At 05:13 PM 9/14/04, "Jamey Wright" <[EMAIL PROTECTED]> wrote: > > >A while back, there was some discussion on voters. I have read through all > >of that. > > >Have you read the two or three voter articles at www.repeater-builder.com > >on the Technical Info page? > >Yes I have. > > >>I am looking to install one here. > > >For what reason? > >Some repeater systems that talk further then they can hear decide to > >add a voter system to try and match the coverage. Others add a voter > >to improve hand-held coverage inside the existing TX footprint, others > >just add a two channel voter at the main RX site to gain some diversity > >reception. What is your reason? > >I want to extend portable coverage. We are in an area with lots of hills >and valleys. OK. So the handhelds can hear the repeater TX, they just can't get back into the system. > >I am planning on bringing my rx sites back on RF and having the rx > >radios at the voter site interface to a status tone (2175 Hz) circuit > >and then feed the voter. BTW Moto tends to use 2175 and GE uses 1950hz > >You are aware that the 2175 status tone is designed for a wired > >system? (where they bring the audio back on leased phone lines). > > >And that doing it that way will require you to run the link TX on a > >7x24 basis? This can get expensive in not only the power bill > >but in replacing links TXs (have you verified that you can get the > >link frequencies there - one per RX site?). Which band do you > >plan on using for the links? 420MHz, 900MHz or 1296mhz? > >What equipment do you plan on using for the main channel > >RXs and the link radios?? And do you have spares? Running > >a link TX 7x24x366 just to keep a tone decoder happy will > >quickly determine if your link system is "continuous duty"... > >What I planned to do is to have the link rx interface to the status tone >circuit and when it sees a valid signal from the far end, it will drop the >tone. That way the links don't have to run 24x7. I don't maintain it but I >know of a public safety system here that does it this way and has done it >for a number of years with no problems. I plan on using MASTR II RXs at >each site and Maxtrac 900 for the links. Generally public safety uses link systems that are up full time - either least phone lines or point-to-point microwave shots. They run the tone over the circuit whenever the squelch is closed for multiple reasons: first to indicate that the circuit is idle, but active, and the newer panels can sense the tone level and "track" a changing level (which signifies a path problem). Picture a fire dispatch system with a centralized TX and voting RXs at each fire station. As long as the RX squelch is closed the idle tone is fed to the phone line, and when the squelch is open the RX audio replaces it. Now you see why my comment that "Running a link TX 7x24x366 just to keep a tone decoder happy will quickly determine if your link system is continuous duty..." Note that voter links (microwave or point-to-point radio) have to be very very very quiet - you can't get by on a 20db quieting, most are 45-50db. > >My question is: > >Does anyone have a circuit to generate the status tones or know of a > >reasonably priced commercially available product. I just don't want to > >re-invent the wheel if someone else has already dealt w/ this. > > >The GE voter used a 1950hz status tone and there was a board that fit > >into the EP-39 aux RX chassis that did just what you want. If someone > >can post that schematic all you need to do is change the cap in the > >oscillator to pick up the Moto tone frequency. > >If it uses 1950 then that is what I'll use. I have read through the >installation/service manual for the voter and apparently misread >the status tone part. Most voting panels have an option to hook a "channel active" signal to the receiver port - when the public safety link system brings a remote RX in via a microwave system the interface is usually done with an "E and M Card" in the microwave chassis. An overly simplified explanation of E&M is that it fakes a PTT and COR while delivering audio... the M lead going active on the far end (think PTT) results in the E lead on the near end (think COR). The E lead is tied to the channel active signal on the voting panel. > >There may be a Moto Spectra-Tac card that does the same thing but > >I am not aware of the card name or part number. And there are a lot > >more GE manuals on PDF floating around that there are Motorola.... > >I have the PDF of the manual for the voter. I have also been looking for >one for the GE MASTR II Aux receivers but I haven't found one yet. So you are using a GE voter? What vintage? Grey with incandescent light bulbs or black with LEDs? > >If need be I have a simple audio oscillator design that I can email > >you that uses an 88mh toroid and a single transistor. My first voting > >panel used this tone gen feeding the normally closed contacts of > >the COR. The relay armature fed the link TX and the normally open > >contacts was the RX audio. A 10 second carrier delay relay "filled > >in the gaps" of tweak signal flutter. The link RX COR dropping out > >told the voting panel that the channel was idle. A bit of elaboration: What we were doing was running carrier-squelch links with long carrier delay timers. Our link transmitters were GE Progress line radios that used tubes and the power supplies had relays in them. All we were after was getting reliable voting while not wearing the relays out with picket-fence signals. Today we'd use all solid state stuff with no relays at all. The idle tone was keyed by the RX squelch. If you listened to the link channel you'd hear the link come up and the user talk, followed by a few seconds of idle tone then squelch closure. If the user was fluttering into the RX you'd hear bursts of voice interspersed with bursts of idle tone. The link RX COR enabled the voter port, and the idle tone detector was left active. The system used a nigh-pass audio filter between the link RXs and the voter (which removed all PL tones). Link IDs were accomplished by keying a 100hz PL encoder. You never heard the link ID on the main channel. >If you don't mind sending me the schematic, I'd appreciate it. I have >a design for one but it uses a crystal reference and the crystal is >not easy to find and it takes way more parts. Send me your voice and fax numbers via private email, and a time range (i.e. 9am-4pm) when we can talk on the phone. I can fax you my standard sine wave oscillator schematic. Do you have a source of 88mh toroids? Picture a toroidal coil maybe an inch-and-a-quarter in diameter with two enameled wire windings that when placed in series gives 88mh with a center tap. These were common in surplus in the 70-s and 80s, but I have not seen any in the local stores the last 5-10 years. This circuit is dependent on that part, or a substitute. My voter experience is over 12 years ago and a lot of details are vague - my comment above about "10 seconds" is probably way off... I know it seemed long, but it was probably not that long. There are folks on this yahoogroup that are much more current and knowledgeable than I am. Anyone want to step up to the plate? Also technology marches on... for example where I used a SPDT relay for switching the link from idle tone to RX audio and back a more modern method would be to use a analog switch IC - and I'll bet that even a CMOS 4066 or 4053 isn't considered current technology... even the later Maxim versions (which blew away the originals).... >Jamey Wright KD4SIY Note that all my comments have been relevant to signal-to-noise voters only. Mike WA6ILQ Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
