[GPS_Standard] -5 to +5 Voltage Source

[Mark Fancher]

I guess I should have planned better before I bought the 10811 oscillator.
I thought these were very popular for these GPSDO projects, but didn't know
there'd be so much difficulty in providing the adjustment voltage to it.

What oscillator is best for the VE2ZAZ board that hopefully won't require
the complex external negative voltage scheme?

Mark

-----Original Message-----
From: GPS_Standard [mailto:gps_standard-bounces at mailman.qth.net] On Behalf
Of Dave Platt
Sent: Saturday, December 13, 2014 10:11 PM
To: gps_standard at mailman.qth.net
Subject: Re: [GPS_Standard] -5 to +5 Voltage Source


> I'm having difficulty understanding how to create the proper voltage 
> source for the VE2ZAZ control board, -5 to +5 volts.  Any suggestions?

There are several approaches.

If you start with a single-voltage supply (say, a +12 or +24 - whatever your
oscillator requires) you can add an additional regulator to get a clean +5
supply for the board's oscillator-control output.  Since you only need a
small current, a simple 78L05 regulator and a couple of filter caps would be
all you need.

The -5 is more difficult.  The most straightforward way is to use a
commercially-made or home-made power supply with both positive and negative
outputs... say, a +/- 15 (these are relatively common) and then use a
negative voltage regulator such as a 7905 to regulate the -15 down to -5.

You could buy a kit such as the Chaney C6895 from Electronics Goldmine...
this has three variable output voltages (positive and negative up to 15
volts, at 400 mA, and positive up to 21 volts at 1 ampere).  This might be
your best bet, if 1 amp is enough to run the oscillator with its heater and
the main VE2ZAZ input - the two low-current outputs could be set to +5 and
-5 and provided to the VE2ZAZ output circuit.

It *is* possible to start with a single-voltage DC supply, and generate
positive and negative voltages from it.  It's a bit tricky.  One approach is
to use a switching-type "inverting regulator" to create the negative
voltage.  Alltronics has a +12 in, -5 out (Astec AA7600), $8 for two.  These
switching inverters might not be a great solution for a GPSDO where you want
really low noise, though.

Another approach is to start with something like a 24-volt DC supply, and
use a 7805 linear regulator to create an "artificial ground" (which then
becomes the "GND" power input to your VE2ZAZ board).

If I were you I'd probably look for a multiple-output DC power supply...
Electronics Goldmine, Alltronics, All Electronics, Marlin P Jones are all
good on-line vendors to check.

And... as an out-of-the-box possibility - although your HP oscillator has a
-5 to +5 tuning range, there's no law that says you have to actually *use*
the whole tuning range.  You could have the VE2ZAZ board put out a tuning
voltage between 0 and 5 (so no negative supply
required) and use the HP oscillator's "FREQ ADJUST" trimmer to rough-tune
the oscillator so that it's right about on-frequency when the VE2ZAZ is
feeding a mid-scale output (2.5 volts) to the oscillator's EFC input.

This would let you get away with just positive power supply voltages to the
oscillator oven, oscillator input, and VE2ZAZ.



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