[App_rpt-users] Hamtronics (was Re: RTCM PTT circuit)

[Bryan Fields]

On 3/8/14, 11:57 AM, Sam Nabkey wrote:
> I totally agree...  I had a Hamtronics 220 repeater and I did exactly that...
> 
> After the audio mods it sounded really nice. 

Since asterisk generates the ctcss, and will do limiting/processing, why would
you not feed it into the modulator directly?

The newer hamtronics PLL exciter boards are quite good.  They don't do them as
a kit anymore so build issues are not a problem (dear god how they were!)
They are all SMT for the most part (less/no microphonics), and they switched
the final transistor from case-collector to a case emitter (BeO insulated) so
the final transistor does not have RF on the case anymore.  It's direct FM,
not PM.

The only thing I use the amp/limiter for is the local mic, and I'm not going
to be doing local mics on my repeaters going forward.

All this said, hamtronics needs a small (BRASS) box they can sell to mount the
boards in.  I've made one out of PCB but it's not perfect and quite ugly.  I
detest wires soldered to the boards in an enclosure so I use some header pins
and solder those to the feed-through filters between the segments.  I remove
the stupid phono connectors and put a proper SMA in place, and convert the
unit so the PLL is always powered.

Box Pics (SFW)
http://gallery.keekles.org/d/28340-2/0308140155.jpg
http://gallery.keekles.org/d/28343-2/0308140155b.jpg
http://gallery.keekles.org/d/28337-2/0307141213.jpg

The units are fairly trivial to sync to 10MHz,  Put a SMA on the board and put
a .1 uF chip cap in line where the TXCO used to be.  I rip out the uP and dip
switches and they are not needed (I'd asked hamtronics to modify their code to
change R from /2048 to /2000 and they said it was going to take weeks and cost
thousands to do it!  Sucks but for $200 bux I got it going with a PIC 16f88).
 Couple this with a thunderbolt 10MHz GPSDO, and you have a frequency
stability in the mHz (that's milihertz).

Now I don't have a simulcast system online yet (working on the prime site
now), but I expect everything should work.  I could be wrong and have already
been a few times, but it's a big experiment :)  There are few commercial 220
repeaters out there, and even fewer that can take an external 10 MHz
reference.  You can convert/buy a micor to 220, but it's a 40 pound and 50
year old radio.  By time you add in the cost of proper channel elements from
ICM it's not worth it.

The hamtronics exciter/receiver are "pure"; no extra crap, no stupid motorola
design issues, if you need to modify it it's easy to get at basic parts.  It's
the basic building blocks, and no more.

Sorry for the teal deer, but it's my thoughts on the subject as I take some
shit for being a hamtronics supporter.


-- 
Bryan Fields

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