GM Eddy:
Even the 100Kc calibrator is going to suffer from start-up drift. At
the very least--and surely acceptable for a tens-of-Hz startup
measurement, just leaving the 751A on for some period of time before
doing the start-up test on the Drake should suffice.
I settled my 751 down an amazing amount by simply surrounding the
primary crystal with an improvised styrofoam "box" and some cotton.
Its all as stable as a crystal can be without some PLL or temp
compensation done on it. I guess the main thing is to use a standard
that is already settled in and warmed up when making the turn-on drift
measurement.
If you haven't been involved in an FMT, (Frequency Measurement Test) the
level of effort will shock you!. But we're talking a few hundredths
(yes, .01) Hz. Small enough so the variations seen in the over-the-air
WWV broadcasts become non-useable when multi-path is present.
What you find out real fast is that if you can control the temperature,
the frequency of most equipment follows along.
Current state of the art is GPS-disciplined rubidium reference
oscillators. It makes my military oven-ized HP reference osc seem flaky!
Any way, thanks for sharing your results. I will be interested to see
how much different they are with a pre-stabilized 751A as the reference.
BTW, if you use a PC in the shack, a program like FlDigi, or Spectran,
(or Spectrum Lab if you are really into it) can help you plot very good
reference information using WWV at 2.5, 5, or the CHU frequency infor.
They plot using an audio reference from your rig. pretty simple really
and easy millihertz accuracy right out of the gate.
Have fun.
Curt
KU8L
On 11/26/2011 7:37 AM, Eddy Swynar wrote:
Hi Curt,
When I get the chance this weekend I'm gonna run some stability tests on the 751A here,
using a 100-KHz crystal calibrator / oscillator as its "umpire"...
You've got me thinking: maybe there really WAS a reason that ICOM offered for sale an
optional "high-standard / ultra-stable" crystal oscillator as option for the
751A back-in-the-day...!
~73~ de Eddy VE3CUI - VE3XZ
***************************************************************************************
On 2011-11-25, at 9:05 PM, Curt Nixon wrote:
Not sure anyone asked this, and I didn't see it in your initial post, but was
the 751A already warmed up when you tested the drake?
What is the frequency reference in the 751A?
I recently used a 751 which is essentially the same frequency determining
set-up for a freq measurement test and I can tell you, it isn't all that stable
either...and, it goes up and down with small temperature differences over a
span of only several minutes. Even when it had been running in Rx only for
over 24 hours.
So..keep in mind that the data you recorded is the net difference from a moving
reference.
After warm-up, I'm not so sure that the 751A is any better than the Drake.
They are a lot better if they have the TCXO module added, but I didn't see that
mentioned.
Anyway, just curious what the reference conditions were.
Thanks
Curt
KU8L
On 11/25/2011 5:57 PM, Garey Barrell wrote:
Steve -
I think 30 minutes is a reasonable 'warm-up' time. IF the radio is in a
controlled environment.!! Take one out of the garage in winter and plug it in,
it's gonna take considerably longer before everything reaches equilibrium. You
have some sizable chunks of iron and steel in there that can absorb quite a bit
of heat. From 60 degrees to a 'nominal' 75 degree ambient on top of normal
internal heating would take a while, perhaps an hour?!? :-)
Plus as Evan said there will be a delta from transmitting as well. A fan makes
a BIG difference in this if you are into long transmissions or TTY, etc. This
is one reason why the TR-7 fan is used to exhaust hot air from the PA right out
the back rather than blow it in all over the radio, including the PTO, with
each transmission.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Steve Wedge wrote:
I always assumed it was a 30 minute warmup, because I seem to remember the
alignment procedures spec 30 minutes warmup before doing an alignment.
Steve Wedge, W1ES/4
"I can't complain, but sometimes I still do."
- Joe Walsh
If the above message appears, it came from Steve's Son of Laptop!
----- Original Message ----- From: "Eddy Swynar"<[email protected]>
To:<[email protected]>
Sent: Friday, November 25, 2011 2:32 PM
Subject: [Drakelist] T-4X Stability
Hi All,
The manual for my T-4X states that stability is "LESS THAN 100 CYCLES AFTER WARM-UP". My
question is simply this: how long, exactly, is an accepted period of "....warm-up"...?
After all of the hoops that I've jumped through in stabilizing the PTO in my rig
(re-buiding it almost, actually!), I decided this morning to actually measure its drift.
I used my ICOM 751A transceiver (in general coverage mode) as the frequency
"umpire", and tuned it directly to the Drake PTO's output frequency of
5454.0-KHz. Both rigs were in the basement overnight, where the ambient room temperature
was 59F. I measured the frequency a total of SIX times, i.e. (1) immediately at the start
of the test, (2) 3 minutes into the test, (3) 15 minutes into the test, (4) 30 minutes
into the test, (5) 1 hour into the test, and finally (6) two hours into the test...
Here are my results:
(1) 5454.0-KHz (cold start);
(2) 5454.0-KHz (unchanged from cold start);
(3) 5453.5-KHz (downward drift of 500-Hz from cold start);
(4) 5453.0 KHz (downward drift of 1-KHz from cold start);
(5) 5452.8-KHz (downward drift of 1.2-KHz from cold start), and,
(6) 5452.8-KHz (unchanged).
So---it looks like the rascal that I have here stabilizes after a good hour of steady
warm-up, which leads me to suspect that maybe "warm-up" to the writer of the
manual was, in fact, just that, i.e. one hour...?
No matter, it was a most interesting exercise---and I sure would be curious if
my rig's performance might match that of some of the other T-4Xs that are out
there...although I dare say, probably not everyone has as thick a hide as I do
in being able to withstand a 59F ambient room temperature...! Hi Hi.
~73~ de Eddy VE3CUI - VE3XZ
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