Jim Lux wrote:
Heck, if you MUST use all analog designs and you're at less than 3GHz,
don't fool with diodes, use the less expensive, more sensitive, and
more accurate power measuring chips from Analog Devices.

Example: AD8310, DC-440MHz, 90+dB dynamic range (-91 to +4dBm) linear
to 0.4dB, stable over temp(-40 to +85) +/-1 dB

or the 8319, 1MHz to 10GHz, 40dB range, similar accuracy


N2PK has published a nice reflectometer design using two AD log chips as
detectors for forward and reflected power. The output voltage of each
detector is accurately proportional to log(power) over a very wide range
of applied power levels. Subtract the output voltages of the two
detectors in an op-amp, and you have a direct indication of return loss
in dB.

Details are at www.n2pk.com (better known as the home of the N2PK Vector
Network Analyser).

By the way, the Analog Devices samples service is also open to amateur
experimenters (by company policy) so by all means let's make use of it.
Many devices are only available in SMD - and many advanced RF devices
simply wouldn't function in a larger package - so as amateur
experimenters we have to bite the bullet and learn to handle SMD.

As Tom says, SMD can be the key to accurate measurements at VHF and UHF,
because the smaller packages have much lower parasitic inductance.

I wouldn't presume to tell Suzy (or anyone else) what they can or cannot
see and handle; but for many people, converting to SMD is mostly about
having the right equipment - a small soldering-iron tip, small-gauge
solder, a good pair of tweezers, and above all, some kind of optical
aid.

If they work for you, one of the best bargains would be a pair of very
strong half-moon reading glasses, worn as a "preamp" on top of whatever
eyeglasses you already wear. It's certainly worth wandering into the
drugstore to try some (pick the strongest they have). Otherwise, there
are many other sources of hands-free magnifying visors. Whoever you are,
see what will work for you.

For people who are acutely short-sighted, ignore most of the above and
simply take off your eyeglasses. At last, your day has come.

Under the magnifier, it's amazing how most people's hands become steady
and tremor-free. (That's in the absence of any medical condition that
can interrupt the eye-hand feedback loop - and also in the absence of a
much more common problem: too much caffeine!) We can't all be
neurosurgeons, but we can become good enough to handle SMD.

And then, as with most manual skills, it takes practice to become really
good at it. For occasional SMD work, it also takes practice to get back
into it after a long break.

The bottom line is that most of us CAN handle SMD... and if we don't
want to become stuck in the late 20th century, we're going to need to
develop that skill.


they also come in dual versions and versions with phase comparators..

The last time I looked, the device with the integrated phase comparator
had fallen off the regular samples service ("contact AD")... does anyone
know more?


--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek