[TMC] VOX/PMO?

W2HX w2hx at w2hx.com
Fri Oct 9 07:59:06 EDT 2009


Thanks very much, Roy. Yes, I did a little research at jptronics archive and
read up on the SBT-series. They all seem to reference the VOX not the PMO.
One thing I am trying to figure out... K4OZY explained it to me but I am
still having trouble getting my arms around it...

Looking at the SBT-1K manual, it seems that there are some configurations,
(N) and (M) are examples, where no VOX is provided. Would this only be used
in crystal controlled situations?

Yet the SBE-2/3 have some kind of tuning dial that seems to cover all the
bands. Is that disabled for crystal control?

So what is the tuning dial doing on the SBE? I can understand if the VOX was
used as a frequency reference and that the SBE had an internal oscillator
that was phase locked to that high stability reference. Then the tuning dial
on the SBE would be adjusting a VFO. But it seems that the VOX has its own
4-64MHz oscillator.

So how does this work in practice? I want to transmit on (say) 3885.  Do I
tune the VOX to 3885 and then tune the SBE to 3885? 

I dun get it!

As for having a PAL, not yet, but I have a line on one (are you going to
Deerfield by any chance?)

73 Eugene W2HX

-----Original Message-----
From: Roy Morgan [mailto:k1lky at earthlink.net] 
Sent: Thursday, October 08, 2009 11:59 PM
To: Eugene Hertz
Cc: tmc at mailman.qth.net
Subject: Re: [TMC] VOX/PMO?


On Oct 8, 2009, at 10:13 PM, W2HX wrote:

> Hi there. I am looking to put together a TMC station using a GPR-90  
> and
> SBE-2 or -3 and PAL-350.

Do you HAVE a PAL-350?  I do, but no power supply.. BIG PROBLEM!   
Building a replacement for the missing PAL supply is a complicated  
job:  change of voltages for different modes (CW - SSB) are done in  
the supply.  All protection, overcurrent cutouts are in the supply.   
(Metering is in the PAL).

> I understand that the SBE requires a frequency source.

The SBE has place for (about) 10 crystals, so if you are doing fixed  
frequency things, like AM on 3885, or TTY on commonly used  
frequencies, no problem.. IF you have the right crystal.

> Can either a VOX or
> PMO satisfy this requirement?

Here I depart from being sure: I think either one would work, however,  
the PMO is meant for "portable" use and (I THINK) does not have the  
frequency multiplier stages that the VOX has, see below (I looked at  
the manuals).

The VOX has:
- A BFO oscillator with two selectable crystal sockets (455 kc typical)
- A master oscillator operating from 2 to 4  mc
- Provision for three selectable crystals (operating 2 - 4 mc four  
output to 64 mc)
- mulitplier stages for output from 2 to 64 mc.
- a 100 kc crystal calibration oscillator
- is rack mounted

THE PMO has
- no BFO oscillator
- oscillator operating from 2 - 4 mc and unit output from 2 to 8 mc
- 100 kc calibration oscillator
- is "portable" but could be rack mounted.

> Or is one preferable over the other?

Yes, for use with transmitter, get a  VOX.

If I remember correctly, the PAL 350 must be fed the frequency you  
want to get out of it.. it does not multiply up from the 2 - 4 mc  
range (as does the GPT-750)

Roy

Roy Morgan
k1lky at earthlink.net
529 Cobb St.
Groton NY, 13073
Home: 607-898-3607
Cell: 301-928-7794







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