[TheList] T500 TX issue

Sun Mar 21 07:29:50 AEDT 2010

You are obviously lucky enough to not be familiar with them. There is a 
multichannel kit that can scan, but there weren't many made and it's a 
painfully slow scan as the PLL doesn't lock very quickly. I don't know 
of any voting on T500's except perhaps the control channel antics on the 
T555TR.

The ESA receivers I did with the external box containing a PIC micro and 
LCD that had the voting used to sense the PLL locking and would wait 80 
milliseconds after that for the mute to open before stepping on. The 
control electronics/display were in the centre console of the car and 
the radios under my seat. It uted the stereo and used those speakers and 
could even be routed to the PA speaker in the front of the car if I 
wanted it to.

They were great units. Ironic thing is, I haven't programmed a single 
PIC in about 4 years now and would need to start again from scratch as I 
no longer have the ASM file I used. In fact I doubt my programmer would 
be workable anymore (Warp

There is no harm in offering to help or provide insight Shane, I'd 
rather see something we can steer in the right direction than nothing at 
all.

As for the transition to digital, I'll miss having the chance to listen 
if I choose, but I must admit I'm not listening that much these days.

Down in my patch, having a voting receiver is quite necessary. My 
personal one had two modified T515's under micro control. One would be 
comparing RSSI of the relevant channels while the other provided the 
recovered audio. Only a single front end and band filter, it splitting 
and being fed to the two receivers just prior to the first mixer. It 
used to swap between receivers regularly, but it was essentially silent, 
frequently changing while there was still loads of signal, a huge 
advantage over the normal T700 receivers which waiting until there was 
practically no signal before doing a comparison.

Good to see some activity on the list for a change :-)

Neill.

Shane V wrote:
> Oops...dam screwed up there...and I was thinking I was doing so well with my
> answer...
>
> -----Original Message-----
> From: thelist-bounces at radiowiki.org.nz
> [mailto:thelist-bounces at radiowiki.org.nz] On Behalf Of Neill Ellis
> Sent: Saturday, 20 March 2010 5:00 p.m.
> To: thelist at radiowiki.org.nz
> Subject: Re: [TheList] T500 TX issue
>
> LOL, Vote or scan mode in a T500 :o)
>
> A brand new T500? That's sad, that unit is 20+ year old technology now 
> and the stopped production well over 10 years ago.
>
> the T550 or T555 UHF versions can only do 12.5 kHz steps, so they can't 
> receive new narrow simplex channels and can't transmit on new narrow 
> repeater input frequencies.
>
> You not only need to clip the diodes, it will also need alignment. There 
> are three vertical pins between the die cast VCO can on the PCB and the 
> diode matrix PCB. Measure the voltage on the center pin relative to 
> ground. You need to adjust the VCO for 4 volts on a single channel. On 
> Multi channels try to keep the voltage close to 4 volts but not outside 
> the 1 and 7.5V range if it varies a lot. Of course you'll then need to 
> peak the receiver too.
>
> Regards,
>
> Neill.
>
>
> Shane V wrote:
>   
>> You may be seeing one of the LO's ramping if the unit is in vote or scan
>> mode...
>>     
>
>
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