asm code for AD9850 to use as 27MHz LNB clock

[Richard-g8jvm]

Hi
I'm stuck and need a bit of help please
I have a GPS locked 100MHz source, and trying to use this as the freq reference for an AD9850 DDS module to generate 27 MHz for the LNB, for QO-100 use. the TCXO I've used moves a little too much for narrow band modes.
I've tried using G4JNT's serial control assembler code changing the reference to 100MHz and the start freq as 27MHz, but zilch is passed to the AD9850
module at power up as I hoped it would, so nothing out of the DDS..
There are a few examples of PIC code on line, but using rotary encoders and displays, lots of unneeded bells and whistles.
Has anyone in the group written or has in their possession some PIC asm code for just loading the AD9850 registers for a single frequency please.

This is holding me back from getting the transmit side built, I'm using a 435MHz TX IF which should make producing some video easier in the future as will be common with anything for terrestrial use
Thanks
Richard g8jvm

[radiogareth]

***SORRY*** I misread which AD device your were using....so this may not be of any use....

Richard, the easiest way of controlling an ADF4351 (and other things) is with Colin G4EML RPri2040 controller, and also now a touch screen version.
They are so cheap and easy to work with....£1.50 from Aliexpress and 20 for a RPI2040 touch-screen version.
Initial article by me in CQ-TV 285 Autumn 2024 p 27, available to members to download from the shop.
Or browse Colins Github. Full of good stuff... https://github.com/g4eml/RP2040_Synth.
Another good fix is to use a QRP-LAbs Progrock2 - the supplied TXCO is very good after a minute. I use it (with a GPS correction option) as a signal source on 10MHz into a ADF4351 up to 24GHz. (7th harmonic used for 24GHz). The GPS correction causes a slight warble but the supplied TXCO is remarkable solid and drift-free, even at that level of multiplication.
Gareth

[Richard-g8jvm]

Thanks Gareth, I'll have a look at that
73 Richard

[g4saq]

Hi Richard,
This may be a red herring for you but I'll tell you anyway, just in case it helps.
I have never used the AD9850 nor the ADF4351 BUT I have helped G4IUG with PIC code for the ADF4351. The code was originally written in C by Alain Fort, F1CJN in 2016. It was later modified by Ron Mount, G7DOE, for use on a PIC. My only involvement was to introduce a 500ms start-up delay to allow the AD chip to initialise properly.
Now, IF the AD9850 is addressed in a similar manner to the ADF4351, then this could be a very simple solution for you as a low pin count PIC would do the job you require. Sorry I can't help with more detail. If you think the code might help, I can send it to you.
73, Russ, G4SAQ

[Richard-g8jvm]

Hi Russ
yes a copy of your code would be handy. I did see the thread about non starting and the 500msec delay you added.
I had the same problem on one of SV1AFN's boards, I fixed it with a 4u7 cap between MCLR and VCC with a pulldown.
I have a couple of 4150 boards and a club pic board.
Its a pity the 4150 doesn't go low enough for my use, unless I set it for 54MHz and divide by 2, hence using a ad9850,, good phase noise, poor spurs, but 27MHz crystals are peanuts so a ladder filter after it will clean that up .
I have been advised that at 9750MHz I will have a 8Hz freq error
Thanks
Richard

[g4saq]

Hi Richard, I've just emailed the .c file to the email address on your QRZ.com page. Hope it helps.
73,
Russ

[Richard-g8jvm]

Many thanks Russ
I'll try that for 1965 MHz ( 1965+435 =2400)
73 Richard