[time-nuts] Re: Current-day GPS timing receivers

[Bob kb8tq]

HI

If you decide to build your ham receiver from scratch, you then head out to
buy a surplus signal generator for < $100 or so. You buy a couple other pieces
of gear, but none of them are as expensive. Back in the day, your TR4 cost way
more than the “bench gear” to do this or that. 

By far, the most likely thing to buy as part of your GPSDO design project is
an atomic clock. Not an Rb mind you , but a properly working Cs or something 
more exotic. ( liike a maser ). The bill for them is way past (>10X)  the price of the
GPSDO. 

Learning wise, you could go to any of a number of Ham Radio / QST / CQ articles
and pick up on the details of how to build you radio. You could even buy any of 
a number of. books that would lead you through the process. 

On a GPSDO, there are no books. There are no magazine articles. The folks who 
design GPSDO’s don’t talk about what’s inside. It’s not so much the individuals, 
it’s how the companies operate. IP matters and it matters a lot. Practical stuff gets
buried as a result. You are off on a “invent it from scratch” expedition (more or less).

Truth in lending: I spend decades doing this and managing folks doing this ….

Bob

> On Feb 18, 2022, at 3:19 PM, Larry Gadallah <lgadallah at gmail.com> wrote:
> 
> Hi Bob:
> 
> I had to LoL (laugh out loud) when I read your message. I definitely
> get what you are saying, but it amused me to no end; When I got my
> first ham license, one of my elmers was the regional distributor for
> Drake, so I announced my intention to take my hard earned cash and
> purchase a shiny new Drake receiver.
> 
> The local elders croaked out: "You don't want to do that. You won't
> learn anything. You should build your own radio from scratch and gain
> some valuable experience." So, here I am some 40 years later, getting
> the exact opposite suggestion. I guess it's true that amateur radio in
> many respects has become merely a tiny slice of the consumer
> electronics market.
> 
> But back to the question at hand: From a purely pragmatic point of
> view, I've been collecting parts for this project for a decade, and
> I'm just thinking that I should either do it, or dispose of the stuff
> and forget about it. You are probably right about needing some
> sophisticated equipment, and we'll see where that leads.
> 
> Seems to me that this is another reality of DIY ham radio these days:
> 75 years ago, you just needed a (wooden) bread board, some brass
> screws, and a tube. Now you need spectrum analyzers, SMT microscopes,
> fantastic eyesight and hand-eye coordination, it just isn't as easy
> anymore.
> 
> 73,
> 
> On Tue, 15 Feb 2022 at 10:25, Bob kb8tq <kb8tq at n1k.org> wrote:
>> 
>> Hi
>> 
>> First question would be “why?” ( or more properly, what are you trying
>> to accomplish? / what are the project goals? )
>> 
>> You can buy any one of a number of GPSDO’s on eBay for very little money.
>> They come in a range of “flavors” from a range of suppliers. You can
>> get OCXO based units. You can get ones based on Rb’s.
>> 
>> Setting up the instrumentation to evaluate a GPSDO design is a bit
>> complicated. Things like atomic clocks and phase noise / short term
>> stability analyzers tend to creep into the lab as a result. That’s not a
>> bad thing. One does need *something* to fill up all that empty bench
>> space :) :)
>> 
>> I would suggest that this all puts a project with a goal of “I want to save
>> money” into the “unlikely” category. If you want higher performance than
>> what you can easily buy, that will require pretty good instrumentation.
>> 
>> Basic choices these days:
>> 
>> uBlox makes a variety of modules. Some are single band, some are multi
>> band. Multi band offers some performance advantages. It also costs more.
>> 
>> The Mosaic-T from Septentrio appears to be the top of the heap right now
>> in terms of mulit band / multi GNSS timing modules.  It has the advantage
>> of being able to work directly with a 10 MHz input and eliminate some of
>> the sawtooth correction “stuff”.
>> 
>> Best guess is that going from a from scratch “idea” to something that you
>> can fully demonstrate works very well is a couple of year sort of project.
>> 
>> None of this is to say don’t do it. The only point is to recognize what you
>> are signing up for before you dive down the rabbit hole.
>> 
>> Bob
>> 
>> 
>>> On Feb 14, 2022, at 9:22 PM, Larry Gadallah <lgadallah at gmail.com> wrote:
>>> 
>>> I'm thinking of reviving a long dead project to build a GPSDO. The last
>>> time I looked, state of the art for GPS receivers was things like the
>>> Motorola Oncore UT+ or the Trimble Resolution T. It's been 10 years (at
>>> least). What better options, if any, are available today?
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> 
> 
> 
> -- 
> Larry Gadallah, lgadallah AT gmail DOT com
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