[TenTec] TT Synthesizer Accuracy (Orion 2)

[N4BE_Jim@yahoo.com]

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 at 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 at contesting.com] On Behalf Of Jim M. via TenTec
> Sent: November 12, 2015 1:51 PM
> To: tentec at 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 calibrate it close to the middle of the HF frequency range, like 14.4 Mhz.
> 
> Thanks, Jim N4BE
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