[NLRS] power measurement

[Gerald]

On Fri, 2006-02-10 at 14:10 -0600, John P. Toscano wrote:
> 
> 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.

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

> 
> > 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?

They once were good, but by the time they got to the hamfest they had
been fried, the smoke had been let out, they have been driven beyond
their power dissipation capabilities, they were toast, burnt to a crisp,
and so "overdone."
> 
> > 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 PAs 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.

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.
> 
> 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 foreseeable 
> 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...

Think about tuning for maximum out or for just enough to drive that
overly sensitive PA. Tuning for maximum out (if tuned through a bandpass
filter that passes only the desired output) works well and can minimize
the spurs from the LO injection and the other sideband. Its conceivable
that tuning for maximum output gets maximum spurs since the LO output of
some mixers is as much as 20 dB above the desired mixing product. Its
also possible that tuning for just the level of output needed maximizes
the breadth of the output spectrum instead of minimizes it.

Even with only relative level devices you can protect that PA by adding
variable attenuation after tuning the exciter for maximum out on the
proper output frequency and them raising the exciter output and watching
the PA output. When the PA output stops rising (or probably the gain
drops by 1 dB) you are at linear saturation and should quit adding more
drive. Even  with a good power meter you may have to do that for
maximizing output without excessive band filling splatter.
> 
> 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

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.

I just added to my microwaves, bought a 1296 module for my FT-736 on
epay from Bob Bonner at Sioux City. So that rig will become the 222/1296
special with other bands maybe covered with transverters to it or to my
brace of FT-857D that hear so much better on 2m and 6m.

-- 
73, Jerry, K0CQ
Dr. Gerald N. Johnson, electrical engineer
All content copyright, Dr. Gerald N. Johnson