Gary:
I believe your assessment is correct, especially in the later firmware versions
that set up the 'cancellation' routine. This also fixed the slight difference
in frequency between the main and sub RX's, or at least radically improved it.
The bottom line is that the only thing that needs to be adjusted is the Master
Oscillator.
I also have an 8640B, a lucky e-bay purchase that works great, but I still
wouldn't trust it for the kind of accuracy I want in my Orion II. Only WWV is
good for that and once calibrated, I use the Orion II to calibrate the 8640B.
Ron Castro
N6IE
www.N6IE.com
Member:
ARRL
Redwood Empire DX Assn.
Northern California Contest Club
Northern California DX Foundation
Society of Broadcast Engineers
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Gary J
FollettDukes HiFi
Sent: November 12, 2015 8:51 PM
To: ronc@sonic.net; Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] TT Synthesizer Accuracy (Orion 2)
I am first suspicious regarding the use of either an Icom 775 or an HP 8640B as
a calibrated reference down to 100 Hz.
I have an 8640B myself and recognize that, despite its excellent design, it
DOES need calibration in order to be “dead on”. I am also not convinced that
the 775 is any better than an Orion as a reference.
That said, he’s look at what TenTec says on the manual:
“The first local oscillator (A PLL) operates 9 MHz above the received signal.
It tracks the 1 ppm stability of the TCXO so its maximum operating error is
10.8 Hz at 1.8 MHz and 39 Hz at 30 MHz.
The second local oscillator is tuned to 8.545 MHz, locked to the same
reference TCXO. Thus, drift in the TCXO cancels when the two drifts are taken
together a the 455 KHz IF (almost).
In other words, there are TWO oscillators with which one must be concerned. If
the TCXO is correct at one frequency, then the first local oscillator must be
correct to the same ppm accuracy since that frequency only depends upon the
reference frequency and the divider number for the VCO (set by the CPU). It
CANNOT be wrong by any other error than the reference oscillator frequency and
that would be related to frequency. You should be able to plot the error and
get a straight line vs. frequency, though the plot line could pass through zero
if the reference is off.
Error in the reference would affect the two local oscillators in opposite
directions, but not necessarily by the same amount. Thus, if the reference is
off, one might be able to calibrate on one band to be correct by the offsetting
errors, the system could be off on other bands due to the fact that the error
in the 8.545 MHz oscillator is always the same but the error in the first local
oscillator is frequency dependent.
It would seem sensible to me to set the reference oscillator directly to its
proper frequency with a calibrated counter reading the actual oscillator output
(as I suspect Ten Tec did originally). Then the system would be forced by the
digital divider to be correct at all frequencies, to 1 ppm (30 Hz at 30 MHz).
Gary
On Nov 12, 2015, at 10:21 PM, Ron Castro <ronc@sonic.net> wrote:
>
> Jim:
>
> I can tell you for certain that it's not in the Orion product line
> since mine generally stays within +- 5 Hz from the broadcast band to 10
> meters.
> In the old days when there were two separate oscillators that
> determined the frequency, tracking errors you described can occur, but
> unless my memory is getting foggy, the entire frequency routine of the
> Orion is determined from a single oscillator module. In that case, if
> you're off 5 Hz on 5 MHz WWV, you would be off 10 Hz at 10 MHz, 15 Hz
> at 15. On ten meters, you would be
> 30 Hz off, all in the same direction, either plus or minus. IOW a
> linear deviation.
>
> If you calibrate the radio exactly on at 15 MHz WWV, how far off is 10
> MHz and 5 MHz WWV? Also check 2.5 MHz WWV if you can hear it, and in
> the day if propagation is good, check 20 MHz WWV. If you continue to
> get the same result, there may be something else wrong that the factory needs
> to look at.
>
>
> Ron Castro
> N6IE
> www.N6IE.com
>
> Member:
> ARRL
> Redwood Empire DX Assn.
> Northern California Contest Club
> Northern California DX Foundation
> Society of Broadcast Engineers
>
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