[Central-Electronics] question on 100V VFO project

[eugene at hertzmail.com]

Thanks Jim and everyone else who responded.  This makes my project much
easier to not have to worry about the mode.

Yes, I know the transmitter will still drift, but this was just a neat
project even if it doesn't improve the performance in any way.

BTW: I do plan to have a mode on the VFO to "adjust" the frequency to
compensate for various other things that aren't 100+ on the transmitter.
This adjustment will offset the radio by +/- 500Hz or something. So when
the display says 14.000 I can make sure its really on 14.000 (even
though the vfo might be at 5.6MHz instead of 5.5 etc).

Thanks again!
Eugene


-----Original Message-----
From: Jim Candela [mailto:jcandela at prodigy.net] 
Sent: Sunday, January 18, 2009 11:34 PM
To: eugene at hertzmail.com; central-electronics at mailman.qth.net
Subject: Re: [Central-Electronics] question on 100V VFO project

Eugene,

    I just looked for a 100v schematic, and I've misplaced mine. That
said, 
if your question applied to a 20a, I'd just put the VFO where you think
it 
should be. No need to offset it like with some of the Drake equipment
where 
the offset varied by mode.

    Another factor is that your DDS VFO even if entirely drift free,
will 
not result in a driftless transmitter. The crystal oscillators will all
move 
around some as they warm up. They will not be exactly on the correct 
frequency either. For example the 9 Mhz crystal in a 20a is seldom on 9
Mhz, 
but they are pretty close. That same oscillator drifts about 100 Hz over
the 
first hour of operation too. On today's bands with SSB, drifting 100 Hz
is 
almost as bad as drifting out of the band. Most ops don't know where
there 
the RIT knob is anymore.

Good Luck!
Jim
WD5JKO
----- Original Message ----- 
From: <eugene at hertzmail.com>
To: <central-electronics at mailman.qth.net>
Sent: Sunday, January 18, 2009 8:10 PM
Subject: [Central-Electronics] question on 100V VFO project


>I have no idea what happened to that email. I spent 15 minutes writing
> and editing that thing and when I hit send, who knows what happened.
> Looked empty in the sent box too. So let's try again.
>
> My DDS VFO project will have a frequency display using nixies. In
order
> for the frequency display to show the proper number, the user (me)
will
> have to input the selected band. So I will try to have a band switch
> like the one on the 100V. User selects, say 20M, I know the mixing
> arrangement and offset the displayed frequency accordingly. Simple
> enough.
>
> My question has to do with emission mode.  Does my VFO need to be told
> what mode in use in order to properly display the frequency?
>
> For example. I set the transmitter to 14.000 MHz CW. The VFO is now at
> 5.5MHz (or thereabouts).  The frequency display should ready 14.000.
>
> Now, if I set my emissions mode to LSB and call up a friend with a
> modern digital readout rig and tell him "meet me on 14.000 LSB" and I
> don't change the VFO frequency, will we be good to communicate?
> Likewise, if after 10 minute ragchew I say, "now meet me on 14.000
USB"
> will we again be able to communicate without me changing my VFO?
(yes,
> I know the conventions on using USB and LSB on the bands, this is just
> hypothetical).
>
> Or, should my frequency display change up/down a little based on my
> mode?
> Put another way, if I change from LSB to USB on 14.000, should I need
to
> adjust my VFO frequency such that the friend with the digital rig can
> understand me properly? Now, I don't mean tweak it, I mean change it
by
> some real, predictable number like +/- 2.8 kHz or something?
>
> Does this question make sense? (I hope so! It's the second time I've
> written it!)
>
> Thanks
> Eugene
>
>
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