Hi

The missing element in your evaluation is phase noise. If you directly multiply any 10 MHz source up to
10 GHz, you have created a noise monster. The only rational way to do it is with a cleanup oscillator (or two)
somewhere between 10 MHz and 10 GHz. There are a variety of reasons why you get the noise increase and
multiple noise floors involved.

If you pick something like 100 MHz as your (first?) cleanup, a bandwidth in the 10 Hz region is not at all impractical
with a narrowband OCXO as the 100 MHz source. For many decades microwave sources have been built this way.
There are lots of designs out there to look at. The power and complexity impact is minimal.

Once you do that,  the only thing that matters on your 10 MHz is it’s long term stability. If you have the power budget,
a Rb is the obvious choice. If not, a DOCXO would be the right way to go. In either case, calibrate them before you
take off on your “adventure”.

Bob

Why to people always build 10MHz GPSDOs?  If the use of the GPSDO is to
drive a microwave, why not build a MUCH higher frequency GPSDO.    Is the
reason that 10MHz crystals just happen to be very good and there are not
good 100MHz ovenized crystals?  Or for portable use could you not use the
1PPS signal to discipline a microwave oscillator.

Scaling up 10MHz is going to make noise, so why not start way higher and do
less scaling

On Wed, Dec 21, 2016 at 11:06 AM, Eric Haskell eric_haskell@hotmail.com
wrote:

--

Chris Albertson
Redondo Beach, California

Chris Albertson albertson.chris@gmail.com (and Bob Camp kb8tq@n1k.org):

Because "a lot" (...) of amateur radio microwave equipment is designed
off the shelf to accept an external 10 MHz input. [And other kinds of
equipment, too.] If you're not designing from the ground-up, then it makes
a lot of sense.

--jhawk@mit.edu
John Hawkinson

I used one of the Jupiter GPS receivers that has a 10 KHz output to control my 10 GHz LO to discipline one of the common "brick" type of microwave oscillators.  These oscillators have an internal crystal oscillator (106.6 MHz  for a 10.224 GHz LO) that is multiplied up to the needed microwave frequency.  I divided the 106.5 MHz oscillator frequency down to 10 KHz that was then compared to the 10 KHz output from the Jupiter.  The control loop is very simple: a single op amp, a resistor, and a large capacitor.  The response time is extremely slow - 5 to 10 seconds or more.  All I wanted was to nudge the crystal oscillator onto frequency. 

The hardest part was designing the divider circuit to get 10 KHz from the 106.6 MHz oscillator.

Tom

WB6UZZ

  From: Eric Haskell <eric_haskell@hotmail.com>

To: Time Nuts time-nuts@febo.com
Sent: Wednesday, December 21, 2016 11:06 AM
Subject: [time-nuts] Using GPSDO as a Refrence for Protable Amateur Radio Microwave Operations

Hello Time Nuts,  I have been on the group and have promoted it to other folks for a while but this may be my first post here.

I am microwave amateur radio operator and I have question to pose relating to the use of GPSDO's with amateur radio for microwave communication.

First, the more generic question.  A friend was discussing using a eBay purchased Trimble 57963-D for providing a 10 MHz refrence for his portable microwave station  (primarly at 10GHz).  He wants a clean high stability 10 MHz refrence mainly to lock the station LO. First I think a GPSDO is overkill for this application and I am thinking that a good surplus ovenized crystal oscillator should get him to within a few Hz after warm up and a Rb could do better but may have short term stability that may degrade phase noise of the LO.  I am concerned that a GPSDO is not designed for portable operations.  Moving it should probably force a new site  survey which may take a day or more  to complete before it goes into disciplining mode so you would loose any potential benefit of a GPSDO by moving around frequently.  If he wants to do this I think he should leave it connected at his home location for an extended time (several days at least), then when he want to go portable (roving), he should
  disconnect the GPS antenna entirely to force the unit into holdover mode maintain continuous power with battery backup which should maintain the internal OCXO very close to the target frequence and allow the holdover algorithm to compensate for OCXO for aging and best it can.  I would guess that if he chooses to used the GPSDO with the antenna connected it would probably never exit the site survey mode and you would have the output default to the last known good DAC value when it was been disciplined so it would be operating as a OCXO only (although potentially starting from a very accurate starting point, if it had been in use at a fixed location for a good while) before going portable.  Is this a correct view of the situation?  Any recommendations?

I also know of a fellow who has developed some excellent open source Linux software to drive an Ettus Research USRP microwave SDR transceiver for amateur radio microwave applications.  His code also has features to calculate antenna baring and with other available code compensates for satellite Doppler shift and/or synchronize digital communication modes using the GPS coordinates and timing data.  He has a built in interface for a Trimble Thunderbolt for this purpose.  I think it also might be a better solution to use a OCXO for 10 MHz and a cheap USB GPS sensor for location?  Is there a cheep USB GPS that provides PPS?  Any recommendations?

I have seen simpler GPS controlled 10 MHz sources like the Miller design that divides down a 10 MHz ref and compares it to a 10 KHz output from a Jupiter T GPS to tweak the ref freq that may or may not be better suited to this application as it may add phase noise to the LO but would be more real time in it's GPS correction to the reference frequency.

Regards,

Norman Eric Haskell

KC4YOE

Keller, TX USA

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It has been done. One I recall is Louis Cupido's Reflock system. TAPR did a
kit for it some years back. Fairly sure there are others.
But there are a number of readily available 'systems'  these days that take
a 10 MHz reference input and generate a 'clean' low microwave reference
frequency output that minimises the required multiplication. The ZLPLL and
the VK3XDK Agile PLL V2 are just two I am aware of.
DaveB, NZ
ZL3FJ

----- Original Message -----
From: "Chris Albertson" albertson.chris@gmail.com
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Thursday, December 22, 2016 3:59 PM
Subject: Re: [time-nuts] Using GPSDO as a Refrence for Protable Amateur
Radio Microwave Operations

On 12/21/2016 2:06 PM, Eric Haskell wrote:

eBay purchased Trimble 57963-D for providing a 10 MHz reference.

As you stated, the time needed for position hold is significant. For my
microwave gear that needs 10 MHz in the field, I use a Jackson Labs
LTE-Lite.

http://www.jackson-labs.com/index.php/products/lte_lite

It can be run in "mobile" mode. I have used it to discipline gear I run
up to 241 GHz. Most of the disciplined LO's are Axtal in the 100 MHz
range. It also supports 'position/hold' mode for use in a fixed position
such as at home in my shop.

There was a group buy a while back.

Frankly, absolute frequency accuracy is a bit less of an issue than it
used to be because so many of us now use SDR's for panadapters on
receive. We can "see" 48/96/192 kHz of bandwidth at once so if a signal
is off a few kHz and moves a bit, no big deal.

If you are trying to do weak signal digital modes, that's another story.

Mike

--

73,
Mike, N1JEZ
"A closed mouth gathers no feet"

On 12/21/16 9:08 PM, John Hawkinson wrote:

In most cases, folks want good close in phase noise - 5 and 10 MHz are
in the sweet spot of having good close in phase noise even after the
20log(N) bump from multiplying it up.  A 100 MHz oscillator takes less
multiplication, but because the crystal is physically smaller, it
probably doesn't have phase noise that is lower than a 10 MHz multiplied up.

if you're multiplying up to 8 or 10 or 32 GHz, whether you start at 10
or 100, it's still a lot of multiplying.  If you're using a PLL, the
frequency gets divided down into the phase/frequency comparator, and
dividing down from 10 is no different than dividing down from 100.
If you're doing chains of multipliers up, then starting a 10 gives you a
bit more flexibility to design the multiplier chain in terms of where
the various frequencies wind up, so as to avoid "inband" spurs later on.

Most ham radio designs tend to be mixes and matches of previous widgets.
The whole transverter model, starting with 10 meters or 2 meters, and
then mixing, converting, multiplying, etc. is great if you're trying to
re-use stuff you already have, gradually adding bands, or trying to use
30-40 year old surplus microwave gear.  It's not necessarily a good
approach if you were starting from scratch and using modern components.

On Wed, 21 Dec 2016 18:59:20 -0800
Chris Albertson albertson.chris@gmail.com wrote:

Short answer:
GPSDOs are mostly about high stability, not about low phase noise.
The 10MHz just happend to be a good compromise on stability, phase noise
and usefulnes.

Long answer:
A GPSDO has to exhibit good stability up to several 100 s to a few 1000 s.
This dictates that the OCXO used has to have as high long term stability
as possible. To get there you need an as thick crystal lab as possible.
The lower the frequency and the higher the overtone, the better.
Quartz resonators exhibit a nearly constant Qf, so in first order
approximation, there is no point in choosing a higher frequency
crystal, as the Q will then decrease and thus increase the phase noise
would have been the same as the increased phase noise of a frequency
multiplier. Of course, frequency multiplication is not exactly perfect and
the Qf is not 100% flat. There is a sweet spot where Q*f is maximal between
5MHz and 10MHz. For historical reasons, 10MHz has been deemed the more useful
value and that's the reason we have a lot of 10MHz OCXO. If you go for high
stability oscillators, you will see a lot 5MHz OCXOs being used (for the
increased stability). Of course nobody says that these are the only
frequencies that can be used. For example, for specialized use cases you
will find GPSDOs with "odd" frequencies (like the 30.72MHz/61.44MHz used
for LTE).

As others have already commented, when using GPSDOs as a frequency reference
for an GHz link, one would use some high frequency oscillator in the lower
100MHz range (using a BAW quartz) or somewhere between 500MHz and 1000MHz
(using an SAW quartz) as a low phase noise reference and upconvert this.
Yes, it is possible to discipline such an oscillator directly using GPS,
but for the sake of stability (see above), design reuse and ease of
building/testing, using an 10MHz input is generally the better solution.
This allows to use any device that can produce an 10MHz signal, like
e.g. an Rb vapor cell standard.

		Attila Kinali

--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson

Well for the same Q a competing oscillator will still take a 20 dB phase
noise increase for every frequency decade you scale up to. If Q*f is
approximately constant, you take another 20 dB hit in phase noise from
degraded Q, totaling 40 dB/decade. Compared to 20 dB/decade plus the noise
introduced by the phase detector and loop-filter of the PLL.
https://en.wikipedia.org/wiki/Leeson's_equation

On Thu, Dec 22, 2016 at 10:53 AM, Attila Kinali attila@kinali.ch wrote: