Re: Stretching the topic slightly for ADF4351 boards


Colin Ranson
 

Hi John -  as you said  “Its quite likely that the stability of the on pcb 25 MHz ref can be improved by insulating the crystal with some polystyrene.”   Mine is in a cardboard box and has been running for two days now on 3400.200MHz, its about 55KHz low and just about stays within the SSB passband of my IC-706MK2g and SG Labs transverter unless subjected to a draft ! – like blowing into the box – then its gone !

 

A die cast box with insulation and plastic push rods (through a thick ally guide plate) for the micro switches is called for.

 

It will only still be a useful play thing not to be incorporated into anything.

 

Regards,    Colin de G8LBS.

 

PS, still looking to buy for a multipole 3.4GHz interdigital filter. Anybody ?

 



 

Sent from Mail for Windows

 

From: Andy G4JNT
Sent: 07 September 2021 09:49
To: UK Microwaves groups.io
Subject: Re: [UKMicrowaves] Stretching the topic slightly for ADF4351 boards

 

The same problem reared its head when the RDDS locking system was developed.   A 10MHz PIC clock interfered with the 10MHz reference and it's sensitive locking circuitry.   The solution was to change the PIC clock to 11.2896MHz

 

Andy

 

 

 

On Tue, 7 Sept 2021 at 09:22, G8ACE <hazellje@...> wrote:

Thanks to all for the additional info on the ADF board with PIC and LCD that I had not seen previously.

A couple of points.  Its quite likely that the stability of the on pcb 25 MHz ref can be improved by insulating the crystal with some polystyrene.
In effect using the pcb as an oven for the crystal.  The actual frequency accuracy may not be improved but improved stability is worthwhile.

I see in the circuit provided by Roberto, thanks, that a 10 MHz clock crystal is shown for the PIC.  If  another 10 MHz crystal is also used for the ADF ref input its pretty certain that these two crystals will talk to each other even when physically a few centimetres apart.  The difference frequency may well produce unwanted spurs.  This was a trap the 122 GHz project fell into when a 10 MHz external ref was added for extra 122 GHz stability.  Using the ADF ref also as an external PIC clock should cure any problem.

73s John G8ACE

 

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