At 05:28 AM 1/19/05, you wrote:
>While we are on the subject of midland/clegg 13-509 radios/repeaters
>has anyone had luck PL'ing the exciter. It wasn't setup originally for PL
>encoders. Initial attempt exciter+PL audio wasn't very promising with a
>TS-32. Looks like you'd have to FM the varicap directly. Was going to use
>some I have as link radios and wanted to PL the link.
>
>tnx,
>Ralph W4XE
Twenty years ago when the Midland was popular the locals
went round and round and discovered that you could get
usable PL by injecting tone through a series resistor (the
TS-32 had a series cap) into the base of the transistor
following the dev pot (i.e. a standard resistive audio
mixer design).
On the other tentacle back then I did a proof-of-concept
exercise and resolved an argument by taking a Moto
station TX channel element (normal elements had power,
ground and output, true FM elements added a mod pin)
and picked one that was on a frequency that multiplied
up to somewhere in the 220 band... maybe 147.81 or
87.... maybe a MARS element on 148.something or
149.something, I forget.
I do remember that the Moto element produced a tripled
output....
I wired the element output into the Midland exciter and
matched levels with a couple of resistors. I then injected
the PL into the element mod pin and had a very clean PL
tone - cleaner than the stock phase modulator...
I won the bet and it got me a steak dinner...
My notes have vanished over the years, but it would not be
difficult to do over again.
These days you could use a much more common Mitrek
TX element instead of using a rather rare Micor station TX
elements and it would work just as well... The Midland mic
audio would need a pre-emphasis network added before it
drove the element mod pin, but you could look at the Mitrek
exciter schematic and start there....
Or better yet just take a high band Mitrek with a blown up PA
deck ($5 on ebay) and take the final 75-to-150mhz doubler stage
and triple there. That would give you 200-300mw on channel.
Or take a UHF Mitrek and change the multiplier chain from
75mhz-doubler-then-tripler-to-450mhz to 75mhz-tripler-225mhz.
As an experimental item I'd look for something around
148 to 149MHz or 446 to 447MHz as a starting place to
play... if it works out you can then order a 220 rock ...
Mitreks are a helluva more common than Midlands....
Better built too.
And the manuals are a helluva lot more common.
My Midland 13-509 and 13-513 service manuals
evaporated a looooong time ago.
Finally, remember that the Midland 13-500 2m radio
and the 13-509 220 radio are twenty-year-old radios.
They were built as cheap as CBs of the era, and
on the same production lines. But we hams built
repeaters out of them because that's all there was.
I really, really suggest that you look at Mitreks and similar
newer radios as 220 candidates. Kevin and Scott Z. have
spent untold hours perfecting the 220 Micor and Mastr-II
conversions and are GIVING AWAY their technology here.
If you need something the size of a Midland 13-509 then
take a GE MVP with a blown up PA deck and do the
Mastr-II mod on it.
Mike WA6ILQ
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