LF: Re: [rsgb-lf-group] [600MRG] Bad news / help request

[N1BUG <paul@n1bug.com>]

Hi David,

Comments in line...

> Oh dear.   That's not good.  It also seems to be out of
> spec....0.5ppm  for a fairly large temp range.

My manual says 0.5 ppm at a fixed temp of 25C, +/- 1 ppm over a wide
range.

Mine may be out of spec but this kind of drift seems to be common
with the FT-2000. Other owners of the rig have commented on it since
I posted looking for help with this, and more in other forums in the
past.

> Isn't it the case
> that if you use the radio on 2 MHz the stability will be 5 times
> better?

Yes, that is right but still looking at significant drift.

> Perhaps you can divide down the OCXO and take advantage of
> the better stability at lower frequencies.

Perhaps but it won't be that simple. My station is quite complex.
The way I get drive for converters is integrated into automated
station band switching which in itself is complex almost to the
point of disbelief. :-) The level of complexity keeps me from
inadvertently destroying things when switching bands but it comes at
a price when trying to add or change capabilities.

The rig is set to 10W output into a custom attenuator. This was
originally designed for +10 dBm for VHF/UHF transverters. The
adjustable series element of the attenuator is a trimmer capacitor
(it's what I had) so the output level is frequency dependent. At 10
MHz it gives about 0 dBm, which after mixing provides the -6 to -7
dBm I mentioned to you in an earlier conversation. This is then
amplified (by one of your amplifiers) to the correct level to drive
everything following. I haven't yet measured, but I would guess -10
dBm or less out of the attenuator at 2 MHz, which will then require
amplification in order not to mess up everything downstream from there.

I would also need to replace the mixer. The present one doesn't do
well below its rated 5 MHz minimum on the RF and LO ports.

I would need to find a design for the divide-by-5.

All this can be done of course, but it would not be a quick fix.

> Also, if it's internal
> heating, can you avoid that by using the transverter output?

The transverter output on this rig only works in the vicinity of 28
MHz. The only way to enable it is to select a "custom" band which
sets the radio to that frequency.

...

Failing new ideas I am leaning toward investing 150+ USD in a low
end GPSDO / synthesizer to replace the FT-2000 TCXO. I view this as
a somewhat costly emergency patch but everything else seems less
likely to succeed in the time allotted. I am only considering this
because it's solar minimum and I've run out of time for study.

I've come to view the last two years as a costly learning
experience. Nearly everything I've built, except PAs, fails to serve
my LF operating interests well. I still feel under-educated and at
risk of more mistakes, but am thinking in the long run a direct
audio to LF converter (and vice versa for receive) might be the
better solution for my station. I don't believe I can build and
implement that in time to catch any part of this winter season. Time
is a luxury I don't have much of!

73,
Paul