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From: "Alan Melia" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
References: <001501c68a76$9c02c8c0$0200a8c0@AUG2004><4487EB8A.27171.B415B8@localhost> <7.0.1.0.1.20060608082442.019be388@magma.ca>
Date: Thu, 8 Jun 2006 15:10:00 +0100
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Subject: Re: LF: BBC 198kHz
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Hi Bill fascinating info......would it be correct to say that with the
magnitude of Mike's error, it is the result of a slightly high reference
oscillator ?? The step size is determined by the reference (divided down)
and Mike's steps which accumualate across the 500khz band seem a little too
big. This would of course depend on whether or not there was a sideband
reversal. Of course if you reduced the step size you could finish up with a
constant offset across the sweep.  Maybe there is no way to compensate for
this and it is regarded as "near enough"
I wonder if Alberto has read this as I think he might have an 850.

Cheers de Alan G3NYK


----- Original Message -----
From: Bill de Carle <ve2iq@magma.ca>
To: <rsgb_lf_group@blacksheep.org>
Sent: 08 June 2006 14:01
Subject: Re: LF: BBC 198kHz


> At 04:19 AM 6/8/2006, Mike, G3XDV wrote:
>
> [..]
>
> >I am now convinced my problem is caused by frequency error in my TS-
> >850. Looking at several standards, the errors are as follows
> >(relative to an arbitrary zero):
> >60.0kHz:        -1.0Hz
> >75.0kHz:        -0.8Hz
> >77.5kHz:        -0.7Hz
> >162kHz: -0.1Hz
> >198kHz: +0.1Hz
> >490kHz (using my LF Tx DDS) +3.0Hz
> >Plotting this on a graph shows approximately a straight line. This
> >indicates a progressive error as frequency increases.
>
> The error isn't strictly linear over all frequencies but it is repeatable
> so once you know the error for any given frequency it can be allowed for.
>
> The TS850 uses a combination of PLL's and DDS chips to generate all the
> internal signals it needs - everything is derived from a single 20 Mhz
> reference.  One interesting thing is that the error can be completely
> characterised by measuring it at a particular frequency within any 500 Khz
> block (e.g. 0 - 500 Khz, 500Khz - 1 Mhz, 1.5 Mhz - 2.0 Mhz etc).  Once
> you've measured that error in any block you know it for the same frequency
> modulo 500 Khz (ie the offset for say 1.290123 Mhz is the same as the
offset
> for 290.123 Khz, 790.123 Khz etc).
>
> Another interesting thing is that in many cases the hardware is capable
> of tuning closer to the optimum value than the rig's firmware actually
> allows!  In other words, the algorithm Kenwood uses to figure out the best
> possible values to load into their four (yes four!) 28-bit DDS chips is
> not optimized to always tune to the nearest frequency to the one shown
> on the display.
>
> Based on Kenwood's block diagram of their synthesizer, I wrote a program
> to calculate the actual frequency the rig tunes for any given displayed
> frequency - but I had to offer several choices near the *best* frequency
> because I never did figure out Kenwood's algorithm.  To find the *actual*
> freq the rig's firmware tunes to, I still have to measure the audio output
> with a known frequency input.  Fortunately the steps between possible
freqs
> are big enough that it is is obvious which one they're using given that
the
> error in my measurements (due to sound card sampling uncertainty) is
around
> 1 mHz.  The worst mis-tune I've ever seen on the TS850 was around 58 mHz,
> which would not normally be noticed by HF operators.
>
> Assuming CW mode and 800-Hz tone out, here are the actual offsets (rounded
> to 3 decimal places) for your freqs:
>
> Frequency     Best possible tune          Actual tune
> -----------------------------------------------------------
>   60.000 Khz        799.983            799.960  (40 mHz low)
>   75.000 Khz        799.997            799.967  (33 mHz low)
>   77.500 Khz        799.999            799.962  (38 mHz low)
> 162.000 Khz        799.984            799.984  (16 mHz low)
> 198.000 Khz        800.008            799.972  (28 mHz low)
> 490.000 Khz        799.983            799.983  (17 mHz low)
>
> I'd love to hear from anyone who may have access to the Kenwood firmware
> code so I can make my little program show the "right" frequency every time
> instead of saying "it must be one of these possibilities..."  I wrote
Kenwood
> asking for details of their algorithm but they did not reply to my email.
>
> Bill VE2IQ
>
>