Thankyou for that Peter. I was aware of the phase locking possibilities but
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I've not attempted it. Its certainly worth a try using the SI5351 and 10mhz
reference to lock 'cleaner' oscillators.
Can you provide details, or a URL decribing the basic method?.
ps. I have a ve2zaz query off list. OK with you?
On 21 May 2019 at 13:53, Peter Mulhare wrote:
Hello Mike and Allison,
I am also a member of the QRSS fraternity, and run a Grabber Station in
Northern New Zealand. I have in the past looked for a solution to keep off
the shelf receivers (in particular) from drifting too much. My Station
receiver is an Icom IC-R75, and I wanted to be able to dial set the receive
frequency to better than 1e-9 (+1 part in 10-9), and for it to remain there
over extended periods of time.. Like you Mike, I have a home brewed VE2ZAZ
GPSDO, which outputs a 10MHz signal with an accuracy of a further 2 orders of
10 better than what I wanted. I had noted that the IC R75 (plus the IC706,
and a number of other rigs), source all their internal frequencies like,
BFO/IF Mixer LO´s/etc, from the Rig´s own onboard Reference Oscillator.
I already knew that it is possible to phase lock crystal oscillators
relatively easily, by injecting a suitable stable signal into an oscillator
appropriately, usually in series with the crystal current. I did this using
the 10.0MHz output from my `ZAZ GPSDO, injecting it in series with the
crystal current of the IC-R75´s Reference Oscillator which runs at 30.0MHz,
to my amazement the IC-R75 locked up immediately to the GPSDO! I simply
wound 5 turns of small insulated hookup wire (from ground) over an RF Choke
in the Reference Oscillator´s circuit, which was in series with the
Reference Crystal, and took this out via small diameter coax to an SMA
connector on the rear apron of the receiver, then connected it via a coax
fly-lead directly to the GPSDO output. The RF Choke looked like a small
1/8th watt resistor, and was through hole soldered to the PC board in a
This worked because the `R75 receiver´s Reference Oscillator runs at
30.0MHz (the 3rd Harmonic of the GPSDO output), so the reference oscillator
gets a kick every third cycle to keep it in phase step with the GPSDO. I
have had this arrangement working now for around 4 years with the R75
remaining locked, 24/7 over that period. This method can absolutely tame the
rogue ICOM rigs that drift too much, simply and effectively! There is no
need to do fan modifications, as in the case of the IC706 or IC756 series, or
even to go to using fancy TCXO´s. The next one I do, will be my IC756
Pro3, however I will need to use a phased locked ProgRock (already purchased)
for this, as the IC756´s Reference oscillator runs at 33.16666MHz (from
memory). What I like is that immediately from switch on the rig is exactly
on frequency (as long as the GPSDO is never switched off!) and will never
drift from its intended frequency, over time.
This will work with other manufacturers Rigs too, however the given is that
all frequencies within the rig must be derived from the set´s internal
From: QRPLabs@groups.io [mailto:QRPLabs@groups.io] On Behalf Of
Sent: Tuesday, 21 May 2019 10:43
Subject: Re: [QRPLabs] Experiments with #Progrock Follow-up
Its why I picked on Icom as I've worked people using them on 6 and 2 and they
Chasing them up and down the band is no fun. The FT817 has issues too as
but adding a TCXO helps. there are many other that wander about on 2M.
The IC706 series is notable for many things including phase noise so bad that
banning it from
any multi radio event is considered required. However the fan can be modded
to run slowly
all the time and its a good mod to help with cooling.