[time-nuts] New Member + Basic Questions

Bob Camp kb8tq at n1k.org
Sun Jan 10 14:42:52 EST 2016


Hi

> On Jan 10, 2016, at 1:25 PM, Nathan Johnson <jdownj at gmail.com> wrote:
> 
> Hello All,
> I'm a ham radio operator, for just a few years, and electronics nut for many
> more. I have been reading the archives and trying to learn a bit. I am wanting
> to develop an accurate frequency standard for "lab" and radio use. I see that I
> have 3 basic options that are possible on my budget, a decent OCXO-based device,
> a rubidium standard, and a GPSDO. My current uses are to supply accurate timing
> to a signal generator(not yet purchased, HP 8640/8650-something) and a frequency
> counter(Fluke 1953), mostly used in aligning radios.
> In the near future I am hoping to expand that to a homebrew HF
> transceiver(probably clocking a DDS chip of some sort), and some higher
> frequency(possibly up to 10GHz) transverters.
> So what I have learned so far about each option:
> -OCXO is probably stable enough for what I am trying to do, but by itself
> provides no guarantee of absolute accuracy(I'm looking at the microwave
> operators "weapon of choice", the Isotemp 134-10), has an adjustment pin for a
> tuning voltage, but no idea what an appropriate value is for that voltage
> without access to a more accurate standard. I will probably build an OCXO device
> of some kind anyway as an interim measure while I earn for the money to obtain
> something better, and to validate a distribution amp within the lab etc.
> -Rubidium Standard seems like a very nice idea, but it's still not traceable in
> terms of absolute accuracy(although the adjustment range of the available
> standards appears to be several orders of magnitude better than I am likely to
> need). The available standards are being re-imported from China, with unknown
> hours or life remaining, and in some cases unknown condition. They appear to be
> power hogs. A $200 gamble.
> -GPSDOs have many options available, and are referenced to primary standards.
> Pretty sure this is where I want to go. I'm looking at Item# 231803015799 on the
> usual auction site, and this seems to be everything I need? I also looked at
> item# 111514491254, but there doesn't seem to be any documentation about what's
> inside.

The first item you reference is a Nortel GPSTM with all the “stuff” to make it work other 
than the power supply. If you dig into the archives, there is a *lot* of information on them there.

The second item is a Chinese Ham built GPSDO without the antenna. It has the nice feature
of being actively developed. If you can read Chinese, you can tune in to the lists that have
information on it. 

Of the two, I’d go for the first one from a US seller that I’ve had good luck with.

A somewhat more “do it yourself” option is:

http://www.ebay.com/itm/221852021307?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

combined with a GPS receiver board.  They also are available in a “2 for a bit less” form from the same seller. 

Each item has it’s plusses and minuses. The third item has a pretty clean 15 MHz output for microwave use.
All of the 10 MHz outputs are a bit dirty noise wise if you decide to multiply them up to > 10 GHz. The normal approach
in that case is to lock up a clean 100 to 150 MHz range VCXO to the GPSDO and then multiply the
VCXO output to microwaves. 

All of them are quite adequate to supply a reference to a signal generator or a counter. All are good enough
for normal HF radio use. 

Bob



> Am I missing key points here? Or am I headed on the right path? Appriciate any
> and all input.
> Nathan KK4REY
> 
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