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
>
>
>
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of N4BE_Jim---
> via TenTec
> Sent: November 12, 2015 7:42 PM
> To: ronc@sonic.net
> Cc: N4BE_Jim@yahoo.com; Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] TT Synthesizer Accuracy (Orion 2)
>
> Hi Ron,
>
> I thought I was following your procedure but it's still off at each end of
> the HF spectrum. I know it's probably within the advertised specs but it
> just seems excessive. Below are the O2 frequency readouts and the actual
> tuned frequencies across the bands. I used a known frequency source at each
> of 9 frequencies, rather than rely on WWV at one frequency. The WWV
> reference alignment assumes that once you calibrate at one frequency, the
> synthesizer will track linearly at all other frequencies. In my case, it
> doesn't. I haven't tried a reset yet, that's tomorrow. I have listed the
> O2 readout frequencies along side the actual tuned frequency below. In this
> case, I calibrated the TCXO at 20 meter frequencies and it tracks dead on
> within that band, but error creeps in on bands above and below. I used an
> Icom IC775 aligned to WWV as a reference, in addition to an HP8640 sig gen.
>
>
> If this same synthesizer design is used in other TT radios, which I suspect,
> then this may be a problem throughout the product line. I'm hoping it is an
> operator error. Here are the numbers:
>
> O2 Freq Readout. True tuned freq. Error
> 4.000.000. 4.000.074. +74 Hz
> 7.000.000. 7.000.052. +52 Hz
> 10.090.000. 10.090.032. +32 Hz
> 14.050.000. 14.050.000. 0 Hz
> 14.300.000. 14.300.000. 0 Hz
> 18.120.000. 18.119.973. -27 Hz
> 21.100.000. 21.099.950. -50 Hz
> 25.000.000. 24.999.919. -81 Hz
> 28.100.000. 28.099.900. -100 Hz
>
> jim N4BE
>
> Sent from my iPad
>
>> On Nov 12, 2015, at 9:55 PM, Ron Castro <ronc@sonic.net> wrote:
>>
>> Jim:
>>
>> The only accurate way to calibrate is to use the main VFO and WWV,
> preferably 15 or 20 MHz. Follow the directions for tuning the master
> oscillator found on my website:
>>
>> http://n6ie.com/TXCO%20Calibration.htm
>>
>> The fan mod helps too, but it's not 100% necessary.
>>
>> 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 Jim M.
> via TenTec
>> Sent: November 12, 2015 1:51 PM
>> To: tentec@contesting.com
>> Cc: Jim M.
>> Subject: [TenTec] TT Synthesizer Accuracy (Orion 2)
>>
>> I suspect this has already been hashed over in the past, but I need some
> guidance. I use the TCXO calbration procedure found on the wiki, i.e. use
> SubRx, tune to WWV, adjust TCXO for same tone on USB and LSB. But
> afterwards, the Main RX seems to be off by 30-50 Hz depending on the
> frequency/band. I also use a known calibrated signal source (an Icom TCVR)
> at various freqs to confirm. Conversely, if I modify the procedure and
> instead listen to the known signal source on the Main Rx set for say 14Mhz,
> all is well for that band but then the Sub RX is off. Then lets say I use
> the known source to set the Tcxo when receiving 28Mhz on the O2, then tune
> the O2 down to a lower band, it will be off by 30-70 Hz depending on how far
> from 28Mhz I go. Seems like the O2 synth tracking is amiss. Is this normal
> behavior? My conslusion, unless something is malfunctioning, is DON'T
> adjust the Tcxo using the Sub RX, but rather using the Main Rx with a
> calibrated source. Then maybe cali
> brate it close to the middle of the HF frequency range, like 14.4 Mhz.
>>
>> Thanks, Jim N4BE
>> _______________________________________________
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>> TenTec@contesting.com
>> http://lists.contesting.com/mailman/listinfo/tentec
>>
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