[time-nuts] Using GPSDO as a Refrence for Protable Amateur Radio Microwave Operations

[Dave Brown]

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 at gmail.com>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at 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


> 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 at hotmail.com>
> wrote:
>
>> 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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>
>
>
> -- 
>
> Chris Albertson
> Redondo Beach, California
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