On 3/25/13 8:27 AM, David Kirkby wrote:
On 25 March 2013 14:36, Jim Lux <[email protected]> wrote:
On 3/25/13 7:17 AM, David Kirkby wrote:
The TCXO oscillator is off the board and a separate item, but costs
£40 and then one ideally wants to lock that to a more precise source.
The oscillator will lock to an external 10 MHz source, but then one
needs to buy both a 10 MHz rubidium as well as this 40 MHz TCXO. Hence
I was wondering if there was a cheaper more compact solution, which
just used a rubidium, and dispensed with a TCXO.
The "two box" solution (10MHz ref + 40 MHz synth,e.g. the SRF040R0L) might
be best. A 10 MHz source is more generally useful.
What you really want is a x4 from 10 MHz, *if* your Rb is clean. Some sort
of pair of doublers or quadrupler might be the ticket. (If the Xband
converter has a moderately narrow filter on the 40 MHz input, that might be
pretty easy.. make harmonics, just pick the right one)
Some Rb sources aren't particularly clean, and the external device serves
as a "clean up loop" for things outside the loop bandwidth.
Have you asked the mfr if they can work at 10 MHz input? It might have some
sort of programmable device inside, and he chose 40 because it's what he
had. What's inside the box, in other words?
I think 40 MHz was deliberately chosen. The manual
http://www.chris-bartram.co.uk/SRF040R0L.pdf
(all manuals at http://www.chris-bartram.co.uk/manuals.html )
state "Modern synthesisers work best with a relatively high frequency
reference source."
so I think the choice of 40 MHz was deliberate rather than the case of
he had the bits around for that.
I've been looking at the possibility of my local amateur radio club
getting on 10 GHz. That is the cheapest solution I'm aware of sold
commercially. Though I'm beginning to think that by the time you add a
pre-amp and power amp, a more expensive transverter is actually better
value. The noise figure of the cheaper unit is 13 dB and the output
level -10 dBm. There are other units for about twice the price
http://www.kuhne-electronic.de/en/products/transverter/mku-10-g3.html
which have a noise figure of 1.3 dB and a power output of +23 dBm.
They too can lock to 10 MHz external references.
We were discussing this at work the other day.. There is a weird gap in
stuff available to hams. You have a lot of older designs, with lots of
discrete devices, lots of touch labor, pretty good NF, etc. Then you
have some really crummy stuff (10dB NF or worse). But not much in between.
But given that there are lots of inexpensive MMICs out that cover 10.5
GHz with NF in the 1-2 dB range, it's odd that you can't buy a cheap
LNA/DownConverter using parts from Hittite or TriQuint.
There's plenty of parts to make a reasonably low noise LO albeit with
fairly high DC power (those GaAs PLLs from Hittite draw *watts*)
Our thought was that you have folks who worked out designs in the 80s
and 90s, and basically just replicate those when the orders come in.
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