ROVERBOX - xlock

simple, cheap and traditional microwave VCO locking

ON4IY and ON4CDU -- January 2007

prototype Xlock PCB

0. Xlock?

The Xlock is thought to be a versatile PLL based frequency stabilisation scheme based up the LMX2306 family of chips (2326 up to 2.8GHz). It uses a PIC16F628(A) microcontroller to load the LMX, and to provide some additional functionality. Why another "reference lock" solution? After having tried all available systems, we felt that price and flexibility still were to be improved. Also the LMX has a nice digital lock detect, to be read and processed by the PIC. Possible applications include microwave LO frequency stabilisation. Also works for ADF4106/4107.

FINAL

LMX2306
PIC16F628A
"thru" LO connection
thru/LOin/reference-in are MMIC (MAR or MGA) isolated
External lock LED driven by PIC also displays QRG selection by # blinks at startup
cost estimate: LMX2306 8€, PIC 4€, 3*MMIC 10€, rest 4€, PCB 8€, total say 30-35€

We decided to leave the VCO/RS232 part out - Expanded Spectrum Systems has boards with this setup that work well.
See my Linrad setup.

Latest schematic and PCB and BOM and code

schematic xlock

1. Project status

Breadboard prototype and assembler LMX register loader done
Schematic and PCB done, 10 PCBs available
4 PCB have been populated and build
C LMX register loader and some mgmt functions finished and boards programmed
the setup has been field tested for a year in ON4SHF/P
nov 2006 doing the FINAL board layout
jan 2007 ready to take PCB orders, readying docs
feb 2007 public, most of docs on website

2. Prototype testing and measurement

All prototypes functional, careful soldering of LMX required
"Quick loop filters"

XLOCK 1st run		13/02/06 on4iy

Pin Ref	10	dBm
Pin LO	6	dBm

	1	2	3	4
Pout thru	8	10.8	10.2	8.5	dBm
Vref LMX	4.5	4.5	4.6	4.5	Vpp
Vlo LMX	1.5	0.9	1.35	1.8	Vpp
Loop filter	No – 470K	CDU/no 680R	CDU/no 680R	No – 470K


PIC reads lock, drives external LED to GND
External LED jumper select at startup

Test setup consits of voltage controlled G8ACE OCXO driving DB6BT style 24GHz setup @123MHz LO, whilst receiving a local 24.048.050 kHz beacon based on Neskom OCXO. Reference either G3RUH/N1JEZ /P 10Mhz or HP3801A as indicated.
SpectrumLab (click image for detail, vertical bars are 200Hz apart)

2 xlock samples driven by the simple G3RUH reference listening for the beacon

xlock sample driven bu the HP3801 / open and close feedback loop

xlock first with HP, then with G3RUH/N1JEZ (on same frequency!) / listening while the beacon heats up using HP reference

From the above we can conclude that the xlock contains the frequency in a 100 Hz BW using the simple GPS based reference - about half of that for the HP commercial reference.

But the proof of the pudding is in the eating, audio proto1 proto2 proto2-withhp proto3

3. Todo

Loop filter optimization: done 2/2006
In-depth testing (noise immumity, RF aso): done 2/2006
Systems integration into ON4SHF contest station for field testing: done 3/2006

Revise artwork: 11/2006
Finish host and PIC code to send and process arbitrary N/R values: cancelled
Write-up/publish: target CJ2007

Author: on4iy@qsl.net. Version: Tue Jan 31 14:32:42 MET 2007