EMRFD Message Archive 549
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,
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
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
skirt depth of over 65 dB is displayed. Then, changing the verticle
sensitivity to 10 mV/grid and using the adjustable slideback feature
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
be 3.2 kHz - "horizontal" is not conveniently calibrated on the
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
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
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!
551 2007-03-21 14:17:55 Bill Noyce Re: Power Meter Application Example On 3/21/07, bkopski <email@example.com> wrote:
>Very nice, Bob ...
> 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
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