[TheList] T500 TX issue

Sun Mar 21 08:25:57 AEDT 2010

Good report Neill, I appreciate the effort taken to write it, and 
enjoyed reading it. Shane, I am not an electrical minded person, so it's 
good to at least see you attempt to answer someones post. This is the 
way us oldies learn.

Neill Ellis wrote:
> 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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>>
>>   
>
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