[time-nuts] A small piece on HP's hydrogen maser in 1968

Jim Lux jimlux at earthlink.net
Wed Feb 26 09:01:20 EST 2014


On 2/26/14 12:44 AM, Hal Murray wrote:
>
> richard at karlquist.com said:
>> Solid dielectric cable and connectors of 3.5 mm size are mode limited to 18
>> GHz.  That is why there is so much stuff rated at 18 GHz as opposed to 16 or
>> 20 GHz.
>
> Thanks.  That's what I was looking for.
>
> Wiki says that SMA works to 18 GHz and the 3.5 mm is good for 34 GHz.
>    http://en.wikipedia.org/wiki/SMA_connector#Variations
>
>

And, as pointed out earlier, the market is smaller, so volumes are 
smaller, and driving the price down from being able to change to truly 
mass production is harder.

There's also a manufacturing tolerance issue.  The higher you go, the 
tighter the mechanical tolerances get.  I suspect there is a huge amount 
of tooling out there for SMA connectors and other things of that size 
where the machining tolerances are "good enough" for SMA and 18GHz, but 
not "good enough" for higher.

That drives all sorts of things.

THere's also semiconductor parts.  Lots and lots of stuff in the under 
12-13 GHz range that are inexpensive.  A fair amount up to 18-ish, and 
then it sort of falls off.

There, it's driven by market, which in turn is driven by international 
allocations.  DBS satellites at 12-13 GHz is a high volume market, so 
there's lots of things like MMIC low noise amplifiers.  Likewise 
anything around 2.45 or 5.1-5.8 GHz.  You see a big break in RF 
equipment model capability at 3GHz and 6GHz, and I suspect that's driven 
by the desire to test cellphones and wifi and BT (<3 GHz) and 
802.11a/802.11n, WiMax, etc at <6GHz.

Parts that are cheap and easy to use lead to interesting products like 
the SignalHound spectrum analyzer, but I don't expect to see a 50GHz 
SignalHound any time soon. ($900 for 4.4 GHz, $2k for 12.4GHz).  You 
could probably *build* a front end converter for a signal hound fairly 
inexpensively, but the parts for, say, 32 GHz would cost as much as the 
Signal Hound backend.


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