Message	Date	From	Subject
549	2007-03-21 13:39:04	bkopski	Power Meter Application Example
Hi All - As a followup to the recent thread (eg my post # 531 et al) about the nifty RF power meter originally published by Wes, W7ZOI and Bob, K7PUA, in QST, June 2001, and my variation(s) in QEX, May-June 2002 and QEX, Sept-Oct 2003, I'm posting two photos illustrating one application of the latter version. The photos "Filter 10dBgrid" and "Filter 1dBgrid" are 'scope displays of frequency sweeps of a 6 crystal 10 mHz filter using a home brew limited range sweeper as the source and my Power Meter variation as the detector. The swept source outputs a sweep ramp signal to drive the 'scope horizontal display. My meter outputs "video" at 100 mV / 10dB and so with the 'scope verticle gain set for 100 mV/grid, a filter skirt depth of over 65 dB is displayed. Then, changing the verticle sensitivity to 10 mV/grid and using the adjustable slideback feature on my meter, the filter passband display is expanded for a magnified / detail look - now at a scale factor of 1db per grid. I used these display features during filter tune-up to yield this result. The HB sweeper / power meter combo made this process quite easy to do. In the end, it is clear that the passband ripple is less than 1 dB p-p, and I believe an even greater skirt depth could be displayed if I had more signal power since the meter dynamic range is greater than shown here. Incidentally, the 6dB passband for this filter is manually measured to be 3.2 kHz - "horizontal" is not conveniently calibrated on the display photos although the horizontal sweep is linear with frequency. Also, note that another variant of the original power meter was published by Roger Hayward with associated coverage in both QEX and QST at dates later than those above but which I don't have handy at this writing. I recall seeing these references in the related thread, however. Roger's version was PIC based with many operational features. Finally - as I see it - you just gotta have one of these instruments if you do any kind of HB'ing at all. It is more involved to build than the classic simpler diode detector based RF voltage probe measurement approach but VASTLY better in ALL respects! Bob, K3NHI
551	2007-03-21 14:17:55	Bill Noyce	Re: Power Meter Application Example
On 3/21/07, bkopski <kopskirl@netcarrier.com> wrote: > > ... > The photos "Filter 10dBgrid" and "Filter 1dBgrid" are 'scope displays > of frequency sweeps of a 6 crystal 10 mHz filter using a home brew > limited range sweeper as the source and my Power Meter variation as > the > detector. Very nice, Bob ... Can you tell us more about your sweeper? I'm especially intrigued by the claim that frequency is linear with the scope's horizontal sweep (or v.v.) -- are you using a DDS? -- Bill, AB1AV
558	2007-03-23 08:06:45	bkopski	Re: Power Meter Application Example

Hi All -

As a followup to the recent thread (eg my post # 531 et al) about the
nifty RF power meter originally published by Wes, W7ZOI and Bob,
K7PUA,
in QST, June 2001, and my variation(s) in QEX, May-June 2002 and QEX,
Sept-Oct 2003, I'm posting two photos illustrating one application of
the latter version.

The photos "Filter 10dBgrid" and "Filter 1dBgrid" are 'scope displays
of frequency sweeps of a 6 crystal 10 mHz filter using a home brew
limited range sweeper as the source and my Power Meter variation as
the
detector. The swept source outputs a sweep ramp signal to drive
the 'scope horizontal display. My meter outputs "video" at 100 mV /
10dB and so with the 'scope verticle gain set for 100 mV/grid, a
filter
skirt depth of over 65 dB is displayed. Then, changing the verticle
sensitivity to 10 mV/grid and using the adjustable slideback feature
on
my meter, the filter passband display is expanded for a magnified /
detail look - now at a scale factor of 1db per grid.

I used these display features during filter tune-up to yield this
result. The HB sweeper / power meter combo made this process quite
easy to do. In the end, it is clear that the passband ripple is less
than 1 dB p-p, and I believe an even greater skirt depth could be
displayed if I had more signal power since the meter dynamic range is
greater than shown here.

Incidentally, the 6dB passband for this filter is manually measured
to
be 3.2 kHz - "horizontal" is not conveniently calibrated on the
display
photos although the horizontal sweep is linear with frequency.

Also, note that another variant of the original power meter was
published by Roger Hayward with associated coverage in both QEX and
QST
at dates later than those above but which I don't have handy at this
writing. I recall seeing these references in the related thread,
however. Roger's version was PIC based with many operational
features.

Finally - as I see it - you just gotta have one of these instruments
if you do any kind of HB'ing at all. It is more involved to build
than the classic simpler diode detector based RF voltage probe
measurement approach but VASTLY better in ALL respects!

Bob,
K3NHI