[Lowfer] R75 Frequency Accuracy

[John Andrews]

Pat,

Like Dex, I keep the R75 on all the time, so the warm-up period is not a 
factor. I don't use an upconverter, so I am receiving directly through 
the R75. The R75's shortcomings have been overstated, but I really don't 
want to get into an argument over it. It has worked out very well for me 
in all applications.

Regarding calibration, it would be worth the time to take the top cover 
off, and adjust L2 in the PLL unit. I would recommend doing that up at 
10 MHz, since you now have a good source. You can do this with Argo, 
assuming that you have done the sound card calibration first so that the 
only error would be in receiver.

At LF, my R75s are both within a couple of tenths of a Hz of being on 
frequency.

John, W1TAG

On 1/23/2013 6:37 PM, pbunn at patbunn.com wrote:
>
> I have an older R75 that I bought 15 years ago and rarely used until
> recently.
>
> I use it for LF work with a home brew RX up-converter and it has worked
> well but frequency accuracy has been quite a bit off. I attributed this
> to my up converter being a bit off and combined with the R75 error
> combining to cause the problem.
>
> Recently I have added a Trimble Thunderbolt and have begun to find out
> where the error is. My up-converter is now phase locked to the GPS 10
> Mhz output and yet my receiver is still 8 Hz off .
>
> Is this more than might be expected from a typical R75 or normal. It
> seems somewhat excessive to me. I plan to add W1VDs circuit to add GPS
> control to the R75 but want to make sure that the R75 is not excessively
> out of spec.
>
> The sound card was calibrated with a GPS disiplined 1KHz signal and
> found to be within .1Hz using ARGO before calibration so the error is
> not there.
>
> Any comments would be appreciated.
>
> Pat
> N4LTA
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