Steve Kavanagh wrote:
"Ian White, G3SEK" wrote in message
...
Instead, I would use the base-emitter junction of a
small-signal UHF/microwave transistor. It seems that just about any
junction that goes into avalanche breakdown at a reverse voltage of 5-7V
will give an Excess Noise Ratio of about 35dB. With a modern SMD
package, the device parasitics will be lower than the wire-ended diodes
that NC were offering, so the ENR will be flatter with frequency into
the microwave region.
That's an interesting suggestion...but presumably the 35 dB ENR can't
be counted upon to the level needed for measurements without
calibration.
That's correct; it is only a design guide to the amount of attenuation
that will be needed to give an ENR that's in the right ballpark. But
then you need to know what the actual value *is* - and for that, you
still need a calibration.
The DJ9BV articles (in both English and German) are on the DUBUS
website, at:
http://www.marsport.demon.co.uk/archive.htm
Look around 1990, and there are a few follow-ups in later years.
(Unfortunately both archive sites are down right now, but do keep trying
- these articles are *exactly* what you've been looking for!)
Thanks, Ian. I found the DUBUS articles...though I haven't read them
through yet. They look very interesting. Though perhaps not *exactly*
what I was after, as they use a real microwave noise diode, whereas my
thrust is more in the direction of what can be done with more common
parts and without any need for calibration of individual noise
standards.
My point was that you don't need a real microwave noise diode - any
small, cheap UHF/microwave bipolar transistor will give almost the same
performance up to several GHz.
I recognize that this probably won't be possible in the
microwave range but it seems likely (to me, anyway) that reasonable
accuracy (not good enough for EME preamps !) can probably be attained
up to VHF, even with these constraints.
You can optimize NF using an uncalibrated source, but with this kind of
source you cannot can make worthwhile quantitative measurements without
an external calibration.
--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek