Phase Noise at 24 GHz

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G8GKQ
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Phase Noise at 24 GHz

Post by G8GKQ » Thu Dec 21, 2017 8:37 pm

I have spent the last few days optimising my 24 GHz system, built in the main from DMC modules, for DATV. The challenge has been to reduce the phase noise of the ADF5355 local oscillator source to acceptable levels. The ADF5355 runs at 11.805 GHz, is amplified in an old Sat LNB preamp to +10 dBm and then doubled in a "Franco" doubler.

Initial tests gave good results on narrow band (with a fairly pure tone from the Bell Hill 24 GHz beacon) but MiniTioune would not achieve a lock on DATV signals. I then applied the modifications detailed in this month's ScatterPoint to reduce the on-board power supply noise, and also enabled the clock doubler and increased the charge pump current as suggested by G4JNT. Both these modifications were needed to reduce the phase noise to an acceptable level. The effect of the noise can be seen on the received constellation plot below, with the elongated quadrant responses. The effect of the noise seemed relatively independent of SR; it has similar effects at 333KS and 4MS, but I suppose that depends to some extent on the noise spectrum.

I do plan to publish the ADF5355 parameters that I used, and make a PIC program available for the "ADF4351" PCB sold by the BATC shop that will work with the ADF5355, but I think that there may be scope for more optimisation, so I'll try this first.

Today's 2-way contact was 29 km, and confirmed that the ADF5355 is usable at 24 GHz. After equipment modifications, Noel and I hope to start increasing the distances.

Dave
G8GKQ
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F1CJN_alain
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Joined: Thu Jul 21, 2011 9:50 am

Re: Phase Noise at 24 GHz

Post by F1CJN_alain » Mon Dec 25, 2017 8:22 pm

The green chineese ADF5355 boards are from two types. The new one is with a correction for noise (see image)
The missing C21 and C37 were connected, before, between the BYP pins and ground . It is not the right place!
Near the LT1763 regulator C21 and C37 are missing and place in the better place between pin 2 (REF)and pin 4 (BYP).It is a better place.
Normally they must be connected between BYP (4) and OUT (pin1).It is the right place in the LT1763 doc.
Note : they are using LT1763 with an internal 1.22V reference and voltage divider R3/R4 for 5V and R6/R7 for 3.3V.
Image

Unfortunately my board is with C21 and C37 soldered in the wrong place. So I did the GM8BJF mod with à 470uF connected between J1 and GND to reduce the noise. Thanks.
Are you using a "new corrected" or "old" chineese card" ?
Best 73's
Alain F1CJN

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