Joe, the question is whether the DDS spurs and noise on the FE-5680A are strong enough to interfere with your measurements.  I suspect that in the HF/VHF range, you'd probably be OK, at UHF maybe dicey, at microwave probably not good (assuming you're multiplying the Rb up).

I have phase noise measurements of the "narrow DDS" version of the FE-5680A along with some other low-cost Rbs at http://febo.com/pages/oscillators/rubes/

73,
John

On Oct 30, 2012, at 8:28 PM, Joseph Gray jgray@zianet.com wrote:

Hi

Simple - feed it in at the high side of the crystal.

Still easy - pop out the crystal and feed it in there.

More complex - re-wire the base of Q101 so it's detached from all the caps and crystals. It's now a comm emitter buffer. AC couple the signal in there.

Of course you still have the problem that the output of the FE is very messy at RF.

Bob

On Oct 30, 2012, at 8:28 PM, Joseph Gray jgray@zianet.com wrote:

I would question the ability to change it. Not familiar with the radio, but
fcontrol feeds back to the 12.8Mhz oscillator by a varicap. If its part of
the pll of the radio then no. If its a RIT control then as mentioned yes.
The RIT will no longer work.

Regards
Paul
WB8TSL

On Sun, Nov 4, 2012 at 7:26 AM, Bob Camp lists@rtty.us wrote:

Can anyone explain the five day delay in Mr. Gray's mail?

-----Original Message-----
From: John Ackermann N8UR
Sent: Sunday, November 04, 2012 6:23 AM

Joe, the question is whether the DDS spurs and noise on the FE-5680A are
strong enough to interfere with your measurements.  I suspect that in the
HF/VHF range, you'd probably be OK, at UHF maybe dicey, at microwave
probably not good (assuming you're multiplying the Rb up).

I have phase noise measurements of the "narrow DDS" version of the FE-5680A
along with some other low-cost Rbs at
http://febo.com/pages/oscillators/rubes/

73,
John

On Oct 30, 2012, at 8:28 PM, Joseph Gray jgray@zianet.com wrote:

Several of the large carriers have had all manner of issues due to the storm;
not only network issues but mail servers as well.

Peter

On 11/4/2012 11:02 AM, Bill Hawkins wrote:

John,

The radio is on 2M.

Joe Gray
W5JG

On Sun, Nov 4, 2012 at 5:23 AM, John Ackermann N8UR jra@febo.com wrote:

On Tue, Oct 30, 2012 at 5:28 PM, Joseph Gray jgray@zianet.com wrote:

The long term characteristics of the Rb are very good.  But short term a
crystal oscillator might be better.  You can have the best of both if you
phase lock a crystal oscillator to the Rb.

This whould give you something more like the GPSDO where the 10MHz output
is from a crystal but there is a control on the longer term drift.  You'd
have a "Rubiidium disciplined XO."

You still need access to some kind of "standard" like from GPS so you can
calibrate the Rb.  Your best bet would be to build a GPSDO that runs
directly at the desired 12.8Mhz.  Most off the shelf GPSDOs run at 10Mhz so
this is a good reason to DIY.

--

Chris Albertson
Redondo Beach, California

Hi Joe,

The reference oscillator is only part of the story.  Being a typical "FM" radio
the normal method is to observe when the carrier is in the center of the
discriminator's bandpass.  The particular center point is not a constant, per se,
because the discriminator is typically adjusted so that the swing of the
modulation is symmetrical and that is not usually at the exact center.  The
discriminator itself may not be symmetrical and often times the center is skewed
because of it.  Therefore you cannot necessarily rely on the center point as
being "on" frequency.  In addition to the so-called reference frequency, you
would also have to stabilize the oscillators that feed the mixers if there is
more than one IF frequency involved, which is usually the case.

The typical stability of these types of radios are pretty good but no where near
time-nuts type stuff.  When transmitting, the heat build up inside the radio will
alter the transmit frequency by a few hertz to as much as few 100 hertz depending
upon the particular radio.  This is normal and usually does not affect the
ability to communicate due to the wide bandwidth of both the IF's and the
discriminator.  At the receiving end you can watch such action in real time over
the length of the transmission.

If you are really trying to do something more in line with timenuts type stuff,
you will, most likely, need to do a different approach.  Perhaps you could give
more details allowing for a better run of suggestions.

As for the FE-5680 Rb, it would require some filtering and such.  Instead of
trying to modify the radio for a direct feed from the Rb it would serve you
better as a source in a PLL type arrangement.

Just my two cents.  So give us more details.

Bill....WB6BNQ

Joseph Gray wrote: