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From: [email protected] <[email protected]> on behalf of Bill Koch <bkoch@...>
Sent: Tuesday, November 12, 2019, 08:49
To: [email protected]
Subject: Re: [ft817] GPS lock the FT-817 for transverter

Whoops…error on FT8 drift in my just sent email…

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I quote from W3SZ’s paper 2/25/2019:

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For example, for FT8 with it’s 12.6 second receive cycle and its tone spacing of 6.25 Hz, the drift of a received tone must be less than 6.25/12.6 = 0.5 Hz/ second in order to maintain channel integrity and obtain satisfactory decoding performance.

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Unquote.

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Sri for confusion

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Bill ??W2RMA

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Greg:

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Your logic is fine.? Rather, the issue here is the expectation of accuracy as well as current practice on the microwave bands.? I am a 10 band rover, with rigs 50-10368 mhz.? For 902 up, I use an external xvtr as well as for 222.? (Maybe the FT817 will someday have 222.)

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From a frequency ‘accuracy’ perspective, good practice these days is such that stations can easily be within < 200 hz at 10368 and better, say, at 1296..? A digiLO or similar unit can create microwave LO signals with reasonable phase noise using a 10mhz OCXO, GPS locked oscillator or Rubidium oscillator.? I use a Morion double oven 10mhz ?OCXO and can run the bands and be on? .100 (or whatever) all the way up.

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From a ‘stability’ perspective, the FT817 is ok for FT8 on 50/144 in a controlled environment (as well as 40M, the only low band I’ve used it on) and sometimes on 432.? However, sun on the FT817 in the field can cause issues as can whether you run output power at ‘1 bar’ or ‘3 bars’.? Moving from an AC house to outside can cause drift.? Any change in ‘heat’ generated inside the FT817 can cause drift.? Recall that the ?allowed drift for FT8 is about 12hz in the 15 second over (per W3SZ’s paper) and that includes your rig’s IF’s LO + xvtr’s LO and is additive to the other guy’s drift.? I know guys who have struggled with stability at 222 with a K3.? ?

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FWIW, I wrote an article on using the digiLO to create the FT817 oscillator frequency.? I built a prototype, but the leakage and therefore cleanliness of the signal weren’t good enough.? TBC.

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73

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Bill? W2RMA? EN90xh

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From: [email protected] [mailto:[email protected]] On Behalf Of nz8r@...
Sent: Friday, November 08, 2019 7:24 PM
To: [email protected]
Subject: Re: [ft817] GPS lock the FT-817 for transverter

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Pardon the inquiry.
I am interested in learning a bit more about upper microwave transverters and their operation.? ?

Do these typically mix the radio (say at 144mhz) as an IF to a multiplied oscillator??
If this is true, the errors would be? something like below:

FT-817 error? ? ? ? ? ? ?=? Ferror
Base oscillator error = Oerror
MultError? ? ? ? ? ? ? ? ?= Oerror * N
Total Error? ? ? ? ? ? ? ? =Terr
Osc's can self start pretty reliably up to about 100mhz....
Therefore N needs to be 100 to 150,? such a large N means Oerror needs to be really small--probably as good as technology will permit.


In the end this is Terr =? Ferror + MultError

It seems the Ferror is really tiny and MultError is huge.? ?
In other words, it seems to me the FT-817 errors are not relevant.

What am I missing as to spending money on fixing the FT817 error,? when 100 times the impact is in the Oscillator errors on the Transverter?

Thanks in advance,

Greg
nz8r