[NLRS] power measurement

[John P. Toscano]

Gerald wrote:

> And while the 432 and 8481B may cover the range, its the least
> expensive, but the heads are the most tender. All I have seen have been
> limited to +10 dBm (on the display and by the power handling of the
> head), none to +44. +44 is at least 20 dB about the point of
> destruction.

It appears that the 8481B is really an 8481A (-30 dBm to +20 dBm) with a 
removable -30dB, 25 watt attenuator.  So that makes a lot of sense.

> The few Narda power attenuators I've seen or acquired at hamfests have
> proven to have been over done and so aren't worth their weight in scrap
> metal.

What do you mean by "overdone" ?  I initially thought "overkill" or "far 
better than necessary" but then the comment "(not) worth their weight in 
scrap metal" connotes the opposite.  So, I'm confused.  Do you mean 
basically worthless, or usable but far overpriced, or something else?

> Now as a practical matter for amateur applications, you aren't likely
> above 1 GHz to be creating power approaching FCC limits so laboratory
> precision in checking that power isn't very critical so the relative
> indications of diode voltmeters (and you don't demand sensitivity below
> 1 mW) can do all you really need.

Yikes, I won't be approaching FCC limits on ANY band as far as my future 
plans go.  To be explicit about what I have and want:

I have four SWR/Wattmeters for the lower 4 bands:

  o Yaesu YS-60 (20W FS to 2KW FS, 1.8-60MHz) which I keep in
    the 50 MHz feed line, My radio is capable of 100W, have no
    external PA at this time.

  o Yaesu YS-500 (4W FS to 200W FS 140-525MHz), one inline
    on 2M and one inline on 70cm feedline.  My external PA's
    for these bands do 170W (2M) and 100W (70cm) max, and the
    drive levels needed are 10W (2M) and 30W (70cm).  The
    radios I have typically have 10, 20, or 50W max on 2M and
    50W max on 70cm, so they can easily be turned down to
    match well.

  o NCG/Comet 3000 (5W FS to 200W FS 118-530MHz) inline on
    the 222 feedline.  My external PA does 110W out for 2W in,
    the transverter is capable of 15W, so I have to watch the
    drive levels very closely.

I have a Diamond SX1000 (5W FS to 200W FS, 4 switchable bands covering 
HF through 2M, 432, 902, and 1296MHz) which I move around for testing as 
needed where needed, since it is the most versatile of the bunch.

On 902 MHz, transverter output is 10W max, and the PA's I have are 3W or 
6W in for 60 or 120W out.  Good match for the meter I have.

On 1296 MHz, transverter output is 3W max, and the PA I have is rated 
for 36W, though I've never seen it approach that.  Good match for the 
meter I have.

This means that I am well-covered for those 6 bands except if I want to 
measure less than a couple of watts on 144 MHz (to check IF drive level 
to transverters, for example) or if I ever go wild with amplifiers that 
exceed 200W on any of the lower 4 bands (doubtful I'd ever exceed the 
250-350 watt range, though).  My 902 & 1296 transverters are currently 
set up for 144 MHz drive in the less than 100 mW range, which barely 
nudges the needle off zero with my existing meters, though I am planning 
to convert them to the 1-10 watt drive level at some point, to match 
2304 through 10368.

I have nothing to cover 2304MHz, where it would be nice to be able to 
measure 3W FS (transverter output is 1.5W) or 1W FS (slightly higher 
than the drive needed by the external PA), and 100W FS (PA is rated to 
put out 60W.)  The Daiwa CN801S (2W FS and 20W FS 0.9-2.5GHz) mentioned 
by Glen (KC0IYT) and Jim (K0MHC) would do the job at both ends of the 
power scale with a 6 dB or 10 dB 100W attenuator...

I have nothing to cover 3456MHz, where it would be nice to be able to 
measure 30mW FS (transverter output is 20mW), 3mW FS (external PA wants 
no more than 2mW drive), and 100W FS (external PA rated for 50W out). 
The Daiwa CN801S was reported to me by two people to give at least a 
relative power reading on 3456, but that doesn't cut it for me, since I 
want to measure both lower power and higher power here with something 
approaching an actual quantity rather than "more" or "less".

Don't have 5760 MHz yet, so no idea what I would need there, other than 
the fact that a DEMI transverter on that band puts out about 2W.

On 10368 MHz, a meter measuring 3W FS would be nice (my transverter is 
rated at 2W out), 1W FS would be nice if checking at less than full 
power, and 10W FS would likely be more than enough for the forseeable 
future (DEMI 8 watt PA someday?).

> . . . can indicate relative power reliably at low cost
> even if bought new. You mostly need to tune for maximum output and you
> are on the air.

Well, yes, if I was just tuning for maximum output.  But I'd also like 
to be able to not only measure the output (how close am I to what the PA 
is supposed to make?), but also monitor the PA input levels, transverter 
input and output levels, etc., as needed to configure or troubleshoot. 
If I simply tune 3456 for maximum (20mW) output and feed that into the 
PA I have, it has been guaranteed go up in smoke!  Fortunately, 
attenuation is easy to come by at the 20mW level, the only question is 
how much is inserted to limit the drive to 2mW, especially if the 
available attenuators are specified to give -10dB only up to 2200 MHz or 
so...

Anyway, I hope that others are considering this to be an interesting 
discussion rather than just chaff filling their inboxes.  I am certainly 
enjoying it.

73, W0JT