Phoenix Rising BBS/phoenixrising.zip/phoenixrising/scanner/rv-m1.txt

Text File | 1994-07-31 | 17KB | 314 lines

Optoelectronics M1 Product Review - September 1993
Copyright (c) 93,94 Brian Mork -- "not to make money, but to keep it that
way for others."

>>> HISTORY
In June of 1993, I distributed a product review of Optoelectronics'
3000A on Packet and Internet networks.  It had bad dBm calculations.  A
July distribution fixed these errors and the text was cleaned up in other
ways.  More complete input sensitivities were reported.  I now have an M1
counter and this review reflects the new experiences.  A third version of
the 3000A review is distributed concurrently.

>>> ABSTRACT
A 10 Hz - 2.4 GHz frequency meter could be a good addition to your shack
if you don't have the functionality yet. The M1 is essentially a pared
down version of the 3000A.  At many places, this review assumes you have
experience with the 3000A or have read that review. The 3000A I owned for
a short while was returned because it was too tender and vulnerable to
real-life conditions.  Since then I've purchased an M1 and intend on
keeping it.  It is my recommendation to most people.

>>> CONSTRUCTION
The case is an extruded U-channel of aluminum with a flat top plate and
end plates.  The end plates screw into the U-channel with four screws,
one of which is a machine screw.  This one is apparently designed to pro-
vide a better "bite" into an interior copper shielding plate around the
input.  The gate LED on the M1 protrudes excessively from the LCD panel,
unlike the 3000A LED, which was mounted to the same height as the switch-
es and pushbuttons.

A single 6.5cm x 11.7cm circuit board lies under the faceplate, directly
mounting the two buttons and five slide switches, which, in turn, poke
through the front plate.  A piggyback (piggyfront?) board holds the LCD
display.  There are two main chips--the OE10 vaulted in Optoelectronics'
marketing literature and an SC87C51.  The two main chips on the board
have a white chalky substance around them as if they were hand soldered
and the flux vapors weren't cleaned off.  Hope it doesn't corrode.  Prob-
ably 200 additional components, mostly surface mounted, also occupy the
circuit board.

The M1 has four battery cells.  Literature claims a recharge lasts about
an hour less than the 3000A.  My M1 ran for 6:50 on a full charge.  The
low battery indicators, although functional during the power-on check,
never did illuminate during the battery run-down check.  The counter just
quit counting and a minute or two later the display faded.
A non-technical review of OE's products (covering more why you'd want
them and what to do with them once you own them) written by Damien Thorn
(Internet [e-mail]) appeared in the August 1993 issue of Nuts
& Volts.  He sounds like he enjoys his 3000A.  I prefer the M1.  The M1
costs $100 less.

>>> OWNER'S MANUAL
It's five sheets of photocopied 8-1/2" x 11", printed in landscape mode
and folded in half.  It's short, but operation of the M1 is easy, so
maybe a lot isn't needed.  I would propose inclusion of a few diagrams
and tables rather than all linear text description.  Included in the man-
ual are:

     Features description............... 2 pages
     Specifications..................... 1 page
     Controls........................... 2 pages
     Data Interface..................... 2 pages
     Block schematic.................... 2 blank pages
     Using the Counter.................. 4 pages
     Battery & Power.................... 1 page
     Calibration........................ 1 page
     Warrantee.......................... 1 page
     Service & Return................... 1 page

A loose sheet of paper gives an overall Block schematic.

The max input ratings match the 3000A.  The 1 Mohm inputs handle a maxi-
mum on the order of 50 volts AC+DC (specified as 100 V RMS in the product
literature flyer).

The 50 ohm switches have MUCH less range! Be sure you *unplug* large
voltage sources (such as TTL) before you slide the switch to the 50 ohm
position.  They handle a maximum of "+15dBm or 50 milliwatts". These num-
bers don't quite match by my calculation (+15dBm is 32 mW).  The range
corresponds to approximately 1.2 RMS in a 50-ohm system, corresponding to
3.4 volts Peak-to-Peak if the waveform is a sine wave.  Accurate numbers
need to be available.

I would suggest making no direct electrical connections to the 50 ohm
amps.  Only antenna type inputs should be used when the 50 ohm amps are
selected.  I've wrapped an 8" wire (snake like) around cordless phone
antennas, and that works ok, but even this would be *way* to much for a
100W HF transmitter.  Be careful and use the bargraph.  Full scale bar
graph ranges from 10-20 mV, depending on the frequency.  This covers a
large range than the 3000A and seems to cover the range of real-life sig-
nals better, but it is less sensitive.

>>> OPERATION
Turn it on, holding down a Button 2 if you want the optional backlight to
come on.  When the backlight is on, I can hear a switching circuit bring-
ing up a high voltage for the luminescent display.  It turns off after 10
seconds of inactivity and comes on again when some button is pressed or
frequency is acquired.

Button 2 selects the gate time (resolution).  With a slide switch, you
select either 1 Mohm (Hi-Z) or 50 ohm (Lo-Z) amplifiers.  The M1 has only
one input, and is incapable of period, ratio, and interval measurements.

If you select Hi-Z input, you can count 10Hz - 50MHz, with a claimed sen-
sitivity of a few tens of millivolts, identical to the 3000A Input A.

If you select Lo-Z inputs, a signal strength bar-graph indication auto-
matically appears and you must select one of two input ranges:

    10MHz - 200MHz (3 stage amp)
    10MHz - 2400MHz (2 stage amp, divide by 64 prescaler)

The M1's 50 ohm input covers the entire range 10-2400 MHz, whereas the
3000A allows selection of 10-220 MHz or 10-800 MHz on the A input and
provides 500-3000 MHz on the B input.  The M1 has slightly less adver-
tised sensitivity (blank entries imply no published specification):

           MHz                 M1                   3000A
          ----                ----                 -------
            10                  5 mV                 5 mV
           150                0.3 mV               0.3 mV
           200                                    0.45 mV
           400                                     0.6 mV
           800                  3 mV                 3 mV
          1000                 10 mV                 1 mV
          2000                                       5 mV
          2400                 50 mV
          3000                                      60 mV

The M1 bargraph has a full scale reading of 10-20 mV, whereas the 3000A
has a full scale reading of 2-4 mV (dependent on frequency in both
cases). It has ten RF bandwidth/display resolution combinations (same as
the 3000A), but because it has only two RF ranges, each range has more
gate time selections.  I *still* don't understand what the sense is pro-
viding more than 6 digits of resolution with a 1ppm time base.  This mis-
leading "resolution" continues to be an Optoelectronics selling point and
is inappropriately echoed by others.

In parallel with all the above input selections, two switches let you
operate in either of four modes.  I'll call them modes 00, 01, 10, and
11, representing whether FILTER and CAPTURE, respectively, are off (0) or
on (1).

   00 (FILTER off, CAPTURE off)  Operates as described above.  This is
      the single mode of the original Model 3000.  Meter shows updated
      values even if it's counting noise.  Gate light blinks continuous-
      ly.

   10 (FILTER on, CAPTURE off)  Computer logic looks for meaningful os-
      cillations, providing a new frequency value only if a legitimate
      count is acquired.  A higher level of filtering can be selected by
      holding down Button 1 during power up.

   11 (FILTER on, CAPTURE on)  Same as mode 10 except nothing happens
      until you arm the system by pressing Button 2.  Once you do this,
      the word "frequency" flashes on the display until a legitimate
      count is snagged.  A three-memory buffer (the display plus two
      more) keeps previous values.  They are referred to as X, A, and B.
      X contains the most recent, A the second most recent, and B the
      third most recent. When a fourth value is snagged, the value in B
      is lost.

   01 (FILTER off, CAPTURE on)  In this mode, no measurements are taken.
      Button 2 rotates between the three memories recorded in mode 11.

>>> PRODUCT SUPPORT
Optoelectronics employees are professional and are helpful on the busi-
ness end of things.  Raw technical knowledge and, thus, the ability to
help diagnose problems or give application suggestions is, in my experi-
ence, limited to only one person.  See the 3000A product review for de-
tails of my experiences.

>>> REAL LIFE
I have two regimes of interest for which I want this counter.  The first
is modem and ultrasonic work in the KHz to 100KHz range.  The second is
radio VFO work, requiring MHz up to GHz.  I characterized the M1 with a
20 Hz - 1 MHz Heath EUW-27 function generator, my Yaesu 757GX/Vectronics
VC300DLP combo, an ADD8000 analog/digital prototype station, a Fluke
8000A DVM, and a Solaritron CD1400 oscilloscope.

--- low frequency ---
For the less than 10MHz work, the Hi-Z inputs must be used.  I have a 2
MHz TXCO standard in my shack that has an output floating on the back
side of a little toroid transformer.  It gives out approximately +-0.8v
with an output resistance of 100 ohms.  The 2 MHz output shows up as a
stable 1.999947 MHz on the M1.  The waveform was not symmetric, but it
was very stable and clean from other high frequency hash.  It looked sort
of like this:

      -.   .---.         The waveform stayed the same regardless of
       |   |   |         whether the M1 was hooked up.  The M1
       | --.   | --      counted the same regardless of whether the
       ./      ./        o'scope was hooked up. P-P voltage was 1.7v.

The 1 MHz TTL tap from the TXCO was a square wave ranging between 0 and
3.8 volts.  Regardless of the M1 filter selection, it showed a stable
frequency of 0.999974 MHz.  These tests came out MUCH better using the M1
than the 3000A.

I next fired up the Heath variable frequency / variable amplitude func-
tion generator.  I needed large amplitudes--WAY above the specified 10-20
mV.  The procedure used was to start at about 1 V and decrease the volt-
age.  If a stable count held, I reduced the PP voltage until spuratic
readings were obtained.  The resultant measured PP voltages (asterisks
indicate I never was able to get a good count):

     Frequency        sine               square
     ---------      --------            --------
      20 Hz             *                 35 mV
     200 Hz           2.7 V               12 mV
      60 KHz          1.8 V               15 mV
     500 KHz          70 mV               20 mV

In all cases, the scope showed clean signals with no high frequency hash.
For the two lowest frequency square wave measurements, hand placement
while adjusting the voltage level significantly affected the required
amplitude.  Best (lowest) voltages are reported above.

The results for the sine wave signals are about 2x worse than the 3000A
Input A response, but incalculably better than the 3000A Input B re-
sponse.  The M1 responded well to square waves whereas the 3000A did not.

I own a PK232 radio modem and decided to see if the meter was good enough
to tune the audio tones.  With nominal output from the PK232 (130mV RMS
on the Fluke, good to 10KHz), I measured the tones with the default digi-
tal filtering of the M1 engaged.  The 2200Hz tone showed as 2272+-1, the
1200 Hz tone showed as 1278+-9 (14 samples each, standard deviation re-
ported).

--- high frequency ---
My RF test goal was simple.  How reliable is measurement of my 757GX VFO?
Working at 15 MHz, the Lo-Z input (only one suitable for this measure-
ment) has an advertised sensitivity of 5 mV.  I used a scanner antenna,
supported about and inch away from a resistor I used as a load.  The
counter's bargraph was about 3/4 scale deflection from the ambient noise.
The transmitter's VFO was allowed to stabilize or about half and hour and
then brought to within 5 Hz of WWV's 15 MHz carrier.  Transmitting 25
watts into the dummy load resistor, the counter hit full scale bargraph
and displayed a frequency of 15.012 MHz.  At 100 watts, the M1 displayed
15.001 MHz.  Accuracy doesn't look so good under reasonable ham shack
conditions, but the M1's 50 ohm input is at least usable whereas the
3000A's was not under similar circumstances.

>>> OPTIONS
You can buy a precision (0.2ppm vs 1.0ppm) timebase for an extra $100.
Again, I stayed away from the 0.2 ppm precision timebase because speci-
fied aging would quickly degrade me back to the standard 1.0 ppm time-
base.  Additionally, I don't often need to know the last 2 Hz on a
10000000 Hz signal.  As with the 3000A, the electroluminescent backlight
is no longer an option-- the standard price is just higher.

>>> GOTCHAS
The serial interface is unidirectional.  You send it a CR and it sends
back 10 digits and a decimal point, in ASCII, 4800bps, 8 bits, no parity,
1 stop bit.  It provides only the most recent number, with no indication
of whether this is another sample or the same number it just sent you
after your last request.  The interface can sink 1.6mA and source 0.06
mA.

Excellent amplifier sensitivity isn't everything.  For decent counting,
the signal you're monitoring must exceed the noise (combination of *all*
other RF signals in the bandpass of the selected amp) floor by a claimed
10-15 dB.  Specified sensitivity ranges from -57dBm to -13dBm.  The input
amp is limited to +15dBm.  Ambient noise, including FM stations hovers
about 3/4 scale on the bargraph when using an AR100XLT scanner antenna.
Since the scale goes from -56 to -26 dBm, that's roughly a -33 dBm noise
floor.  Adding in the 15 dB overhead for a good measurement gives -18 dBm
required signal.  That would be 8 dBm above full scale, roughly 3 bar
segments.  This matches real life experience of the Yaesu 757GX related
above.

The Hi-Z M1 input handles square waves better than sinusoids, whereas the
3000A showed terrible susceptibility to harmonic lock-on with non-
sinusoidal waveforms -- both for me and the other friend spoken of above.
He was trying to measure a frequency multiplying class C VFO and confu-
sion as to which stage was being measured made the meter unusable.  On
another project, anywhere near a 50 KHz switching power supply, measure-
ments were dominated by it.  He asks "would I have this problem with a
TEK or HP counter?"  I don't know.  I know my extensive experience with a
7226B counter in the 1 to 10 MHz range showed none of the bizarre behav-
ior seen with this (and the 3000A) high sensitivity counter.  Triggering
of these counters is just erratic.  Perhaps a DC trigger with variable
threshold adjustment would be better.  OE's digital filtering DOES help,
but often the filter is fooled or else specified sensitivity is unattain-
able.

In Damien's review, he emphasizes the importance of a limited bandwidth
antenna.  Take this recommendation seriously.  The M1's bargraph covers
the range of real-life, on-the-air signals much better; it actually moves
around rather than being saturated most of the time.  The required 10-15
dB spread between noise and desired signal appears as 3 to 4 bargraph
segments on the 16-segment display.  The 3000A and the M1 appear to be
optimized to do off-the-air measurements. In this role, using the M1,
I've had fun snagging frequencies used by all sorts of Air Force base
agencies in a manner just as Damien described.  In the lab, using hard-
wire connections, the Hi-Z inputs of the M1 don't measure up to specs and
the 3000A inputs seem downright unusable.

>>> SUMMARY
Paying $100 less for a M1 balances against having only one input and
loosing the extra modes of operation.  Because these extra modes relied
on the unreliable Hi-Z inputs, I don't miss them.  I am extremely inter-
ested in hearing reports from others in the field that have success or
failure with the M1 and 3000A Hi-Z inputs.

All models are available only direct from the manufacturer in Florida.
Contact Optoelectronics: 5821 NE 14th Avenue, Ft Lauderdale, FL 33334.
800-327-5912 or 305-771-2050.  FAX [phone].  Makes you want to
dial ..2051 and see who you get, doesn't it? :)

73, Brian Mork (Opus-OVH)     ARO KA9SNF@ka7fvv.#ewa.wa.usa
                              Internet [e-mail]
                              6006-B Eaker, Fairchild, WA 99011