10mhz Buffer Amplifier / Splitter
Last edited: 20 February 2018 12:17 AM
The object of this project is to take the 10mhz output of my GPS controlled Frequency standard, buffer, amplify and split the 10 MHz signal into eight 50 ohm isolated outputs to be used as a standard frequency reference by different pieces of test equipment and radios.
On the frequency standard, before the OCXO signal is ready to be used it must be isolated and split into two isolated signals. This is accomplished by a A Mini-Circuit ZSFC-2 Power Splitter. The ZSFC-2 takes the output of the HP 10811A OCXO 10 MHz signal and splits it into 2 isolated 10mhz signals. One signal for the input of the Shera board and the other signal to the input of Buffer Amplifier described below. The two way ZFSC-2 is very important as it provides isolation between the OCXO, the Shera board and the Distribution Amplifier to stop phase noise from creeping into the 10 MHz signal for distribution. A toroid 2 way splitter and 100 ohm resistor like shown in T4 in the schematic below will do the same thing as a ZFSC-2 but I had the ZSFC-2 laying around.
The circuit input utilizes a 2 pole bandpass filter to clean up the input from the OCXO, a 10volt regulated power source, a 2N5109 amplifier running in class A. The transistor output is matched by a L Network to the 50ohm input of the splitter thru a 50 ohm -5dB attenuator. This provides a constant load matching to drive a multitude of toroids in a balanced eight way splitter. The final outputs are each isolated from each other and matched to 50 ohm outputs each. The extra circuit complexity in this design was added to keep from increasing the phase noise on the reference signal. It is very important to keep your reference signal clean and isolated. By isolating each piece of equipment from each other, unintended phase noise will not be added to your reference source. This circuit was designed by Bob Larkin W7PUA.
The PCB layout uses thru hole and surface mount devices. On February 5, 2015, I released PCB Ver1.2. At the suggestion of Bob, W7PUA, I have increased surface mount pad sizes from 0805 to 1206. This will allow you to use either size part and be much easier to see and to solder. I hope this helps you as much as it helps my OLD eyes. The board is only slightly different than the one pictured below. Both work the same and the schematic has NOT changed.
Schematic, PCBoard layout and Parts List downloads are located further down the page.
Circuit was designed by Bob Larkin, W7PUA
Board layout by Jimmy Oldaker W7CQ. (ver 1.2 now available but not shown) (board is 3.8" by 2.5")
PRINTED CIRCUIT BOARD
The printed circuit board is designed by W7CQ on ExpressPCB Software for both the schematic and board layout and is available for free from https://www.expresspcb.com/.
This board is designed to fit ExpressPCB's Miniboard Service in a 3.5" by 2.8" format and as of March 2011, they cost $51.00 + shipping for three identical boards. For a few more bucks you can get the boards with white silk screening and green soldermask as pictured above. At my age, I figure after all those hours of designing the boards, the silk screening and green soldermask it is worth it. Years later and many projects later I have a hard time remembering all those little parts inside the box. The few bucks are worth it to me so I can remember exactly what I did years ago.
You might want to contact a couple of other hams to share a common order of 3 boards. This makes the cost of each board about $20.
I have no plans to produce this board but in the sharing spirit of Ham Radio, I am releasing the design to ham radio operators to use and share on a non commercial basis.
Buffer Amp Download files::
How to Wind Bifilar Coils a one page PDF write-up on how to wind Bifilar Coils with photo.
Schematic after download, can be viewed & edited using the ExpressPCB software.
Printed Circuit Board after download, can be viewed & modified using the ExpressPCB software.
Parts List after download, can be with suppliers and ordering information. Microsoft Excel Format
NOTE: The two ExpressPCB files can be linked together to use for error checking of modifications.
***************** No Warranty *****************
Jimmy Oldaker W7CQ
27640 Gibraltar Loop
Eugene, Oregon 97405
541- 686- 8396
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Copyright 2006 - Jimmy Oldaker Last edited: 20 February 2018 12:17 AM