[time-nuts] 5 MHz from 10 MHz

Robert Atkinson robert.atkinson at genetix.com
Thu Jul 26 04:10:16 EDT 2007

Hi Blair, 
A lot depends on your expectations. If you are not worried about
extracting the ultimate phase noise and jitter performance you should
not have much of a problem.
1. A logic divider (74AC74 or similar) will divide your 10MHz signal.
Bias the input to 1/2 Vdd and capacitor couple the 10MHz signal. The
8640 will take 0.5V to 5V Peak to Peak on its external reference so 5V
logic is OK, I'd put a 47R resistor in series with the output of the IC
and the coax connector. 
2. Square wave is not a problem for the 8640.
3. I don't Know, a multi-coupler seems a bit of overkill unless you have
a couple lying around ;-). They typically have more sensitivity and less
noise than you need. What's the spec of the coupler? Does it provide
overall gain? If you have a 'scope stick a signal into it and see what
level it starts to compress at. If it's a military design for use near
transmitters it should be fine. An output level of 1V Peak to Peak (.7V
RMS) is a good compromise output level.
You may find that a simple transformer coupled 4 way divider will meet
your basic requirement without any amplification. Most commercial
dividers are just a "block" amplifier followed by a string of dividers. 
A possible "off the shelf" solution is a video distribution amplifier,
the type used to feed multiple monitors from one source. You need a
composite type (or an RGB and split your 10MHz into two (or three)
inputs for double (or treble) the number of outputs and use the third
channel for your 5MHz). These are cheap (new on eBay for CCTV etc), you
just want a basic one, no corrections or adjustments.  The input signal
should be attenuated to about 1V peak. 
4. Yes, if you want the best performance and are going to make precision
measurements (HP5370 /2, Wavecrest or SRL TIC's). 

Robert G8RPI.

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Rasputin Novgorod
Sent: 25 July 2007 16:23
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] 5 MHz from 10 MHz

); SAEximRunCond expanded to false
m at febo.com

Hi Guys:

I have a HP Z3801A GPS Receiver Timebase. I was going
to feed it into a HF antenna multicoupler, to discipline
my Harris RF-1310 exciter, Harris RF-590 receiver, HP-8640
generator, and a bunch of other HP test gear.

1) The HP-Z3801 outputs 10Mhz but the HP-8640 wants 5 mHz.
How do it divide it?

2) I presume the HP-Z3801 outputs a sine wave; divider
chips will provide a square wave, is this a problem?

3) The HP-Z3801 outputs quite a strong signal; will it
overload my HF antenna multicoupler? Will the multi-
coupler have enough drive for the other gear?

4) Or should I just quit fooling around and buy a TAPR
Distribution Amplifier?

Guidance greatly appreciated,
/blair VE3CZY

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