[NLRS] power measurement (getting pretty L O N G)

[John P. Toscano]

Gerald wrote:
> I guess I've not been memorizing HP catalogs lately (prices way beyond
> my willingness to spend) so I missed the 8481B.

Since I've been digging out information on the HP power meters, in case 
anyone is interested, here's what I found.  There are also some 75 ohm 
coaxial and some 50 ohm waveguide sensors, but I am omitting those in 
this discussion because I consider them either of little ham interest 
(75 ohm) or probably very hard to find (waveguide sensors)

HP 432A, has 7-position range switch (5 dB increments)
-----------------------------------------------------------
    478A sensor  0.01 GHz to 10.0 GHz  10mW FS to 0.01mW FS
   8478B sensor  0.01 GHz to 18.0 GHz  10mW FS to 0.01mW FS

Newer models of meter, which also have a built-in 1 mW calibration 
standard at 50 MHz.

HP 435A, 435B, 10-position range switch (5 dB increments)
---------------------------------------------------------
  100 kHz to 4.2 GHz sensors
     8482A sensor      3 microwatts to  0.1W FS
     8482H sensor     30 microwatts to  3  W FS
     8482B sensor   1000 microwatts to 25  W FS

  10 MHz to 18 GHz sensors
     8484A sensor    300 picowatts  to   10 microwatts FS
     8481A sensor      3 microwatts to  100 mW FS
     8481H sensor     30 microwatts to    3  W FS
     8481B sensor   1000 microwatts to   25  W FS

HP 437A (digital model)
---------------------------------------------------------
  100 kHz to 4.2 GHz sensors
     8482A sensor      1 microwatt  to  0.1W
     8482H sensor    100 microwatts to  3  W
     8482B sensor   1000 microwatts to 25  W

  10 MHz to 18 GHz sensors
     8484A sensor    100 picowatts  to   10 microwatts
     8481A sensor      1 microwatt  to  100 mW
     8481H sensor    100 microwatts to    3  W
     8481B sensor   1000 microwatts to   25  W FS

All of the above have been seen on eBay lately, and SOME are even 
guaranteed to be in working condition, many at reasonable prices.

> their power dissipation capabilities, they were toast, burnt to a crisp,
> and so "overdone."

Sorry, I guess I was a bit slow on that one.  Got it now!

> Having multiple transverters with different input levels will lead to
> the sensitive ones needing IF interface parts from overdrive in the heat
> of a contest. Conversion to that common level will be good for their
> longevity.

Agreed, that is the goal.  Right now I am "safe" because the 902 and 
1296 transverters are on a dedicated IF radio that can only output a 
signal in the "well under 100 mW range"  (too low for me to currently 
measure), and the 2304 and 3456 transverters are on a different IF radio 
that will eventually drive them all when everything is set up as I want. 
  (The low-power IF rig is a modified IC-251a that I find a bit hard to 
use, which is another reason to move everything to a higher drive level.)

> So one of the Analogue Devices log signal level chips that works to 8
> GHz takes care of much of you're needs. Adding a down converter for
> higher bands seems like it would be simple (and with a 100 MHz to 6 GHz
> IF bandwidth, the LO might not need to be crystal controlled ;<)) and a
> bandpass filter for an elementary spectrum analysis could be a more
> useful instrument than the bare broadband wattmeter.

W1GHZ has a project along those lines.  See:
   http://www.w1ghz.org/new/portable_powermeter.pdf

He uses an AD8307 logarithmic power detector chip for 0-150 MHz with 
good linearity from -70 dBm to +10 dBm, and an LT5508 chip, rated up to 
7 GHz, which he finds usable from 220 MHz up to 10 GHz, although the 
response is not very linear and with a much smaller useful power range 
of -20 dBm to +13 dBm.  In his kit, he uses a simple 10-step LED bar 
display to show approximate power, but the actual output voltage could 
be measured by another device (such as an analog or digital voltmeter), 
and with a bit of intelligence in an added controller chip, could yield 
a (reasonably) calibrated digital display.

It could make a neat project, I suppose, to add the microcontroller 
intelligence and digital display to augment the crude 10-step bar graph. 
  One would still need some external attenuators to measure more than 10 
or 20 mW, as would the older HP432/435/437 meters with most of the 
available sensor probes.

I figured a nice attenuator set would be:
   -40 dB at 100W to make 100 W into 10 mW
   -30 dB at  10W to make  10 W into 10 mW
   -20 dB at   1W to make   1 W into 10 mW
   -10 dB at   1W to make 100mW into 10 mW

I was looking around eBay for pieces to make such a collection, and did 
not find anything suitable unless I was willing to be limited to a 
maximum of 1.5 GHz, 2.2 GHz, or 4 GHz, and some of the prices were still 
high.

I found a retail dealer on the net that sells lots of microwave parts, 
including attenuators that come pretty close to what I wanted:
   www.smelectronics.usa
I never heard of them before tonight, but I was impressed with how close 
they could come to what I wanted:

   -40 dB at  50W to make 100 W into 10 mW (ok, 50 W into 5 mW)
   -30 dB at  10W to make  10 W into 10 mW
   -20 dB at   2W to make   1 W into 10 mW
   -10 dB at   2W to make 100mW into 10 mW

These are all SMA male to SMA female bidirectional attenuators rated to 
cover 0 to 18 GHz!  I found them on the "firesale" page, and they are 
special prices.  In order from top to bottom, $200, $122, $23, and $25. 
  These are brand new and guaranteed.  I can't vouch for the vendor 
(yet), but I did buy a few items from them tonight and will report back 
if I have any trouble with them.  But I have no other financial ties 
with them, just reporting what I found.

Oh yeah, just to "finish" the story...

I bought a used, working HP432A meter with good 478A sensor from a ham 
in the state of MN today, for under $160 with shipping included.  (I 
didn't feel like driving to Madison Lake and back.)

I'm watching a couple of the 8478B sensors on eBay that are rated to 18 
GHz instead of only 10 GHz, even though the 478A sensor is "probably 
good enough" at 10.368 GHz.  If the price of either (or both) stays low 
enough, I may bite.  (Besides, as Jerry and others pointed out, they ARE 
fragile and spares can't hurt.  The ones I'm looking at are guaranteed 
working.)

I'm watching a couple of directional couplers on eBay.  This would allow 
me to sample output power (at somewhere between -20 dB and -40 dB of the 
input power) with a dummy load or antenna on the output end.  Some have 
one sample port, so you'd have to manually flip the connections to 
measure forward versus reflected power, others have both ports so you 
could sample both at the same time.  And you wouldn't need a 50 watt 
attenuator, just a 50 watt load (or an antenna) if testing 50 watts...

And I'm seriously considering buying a cheap cheap HP435A or 435B just 
to get the 1mW calibration output, even if the rest of the meter is 
shot, if the price is low enough.  Who knows, maybe it could be gutted, 
keeping the calibration output and then using the W1GHZ circuit to drive 
the nice analog meter with its dB/Watt scales (with appropriate signal 
massaging).  Another future project to add to the list, as if I don't 
have enough irons in the fire already!

73 (and good night!) from W0JT