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COMPUTING SWR. WHAT SETS THE WM1 APART !
The WM1 Meter doesn't make you stare at crossed needles or make adjustments or do any calculations to read SWR. Instead, like magic, it shows SWR instantly and continuously. So it's a snap to do SWR plots, adjust antenna tuners, or just glance at the SWR occasionally to see that it's still low.
Even when you vary power drastically, such as when adjusting a tuner, the SWR reading virtually ignores the power changes. Just tap the key on CW, or say a word into the mike and you see your SWR instantly in the peak mode. You can easily adjust a tuner while talking on SSB using the peak mode.
AVERAGE OR PEP
The extensive electronics in the WM1 incorporates true peak detectors accurate to 0.1% using op-amps. In contrast, other meters often use just diodes with significant variable voltage drop and questionable accuracy. Switching to the AVERAGE position yields average power. However, the peak decay is sufficient to follow most power changes, and many leave the meter in the peak position at all times.
LOW POWER(QRP) OR HIGH
The meter has 3 full-scale ranges of 20 , 200 and 2000 watts. Half scale on each range is 5 , 50 , and 500 watts. So the meter is ideal for 5 watt CB or QRP, normal 100 to 150 watt ham rigs, or 1500 watt high power. Just select the proper range. The meter is also quite usable at 1 watt for super-QRP, except that SWR will read a little low. Range switching is done with 1% resistors, so when the meter is calibrated at, say, 100 watts, it will be within 2% in power at 10 watts and 1000 watts. Note: Reads power up to 2000 watts at 1.5-30 MHZ, but limited to 100 watts at 50 MHZ.
The meter will not be damaged by overloads. For example, applying 2000 watts on the 20 watt scale will peg the power meter, but the electronics limit current into the meter, so there is no damage. Remember, when you buy a WM1 you're buying a unit that has been "field tested" for over a decade, and it is NOT easy to damage!
REMOTE RF HEAD
Virtually all other meters put the coax connectors on the back of the meter itself. Although this is less expensive, the heavy coax tends to drag the meter across the table when moved. With the WM1, you connect the coax to the remote head which is wired through a 4 ft. flexible wire to the main unit. Most people simply drop the coax behind the operating table, eliminating an eyesore also. You'll appreciate the remote head.
Its accuracy compares with a $300+ lab standard at full or half scale, and includes a meter scale specifically designed for its frequency and power range, not a compromise for various "slugs." So, it's much more accurate at the low end of each scale. And, of course, its total cost is comparable to the cost of just one slug!
RUGGED. A CLASSIC DESIGN
Its case is made of a special rustproof steel, welded at stress points, and so strong you can stand on it! The meters are large. 2-3/8 inches across. It's designed to last for decades.
The WM1 was originally designed in 1986.In the Autek tradition, we took the time and did it right the first time, and there have only been minor changes since. In 1991, we compensated the RF head to make it usable to 54 MHZ. Lately, we made the peak power decay a little faster in response to requests. Lastly, we added lighting on both meters in 1999.
Thousands of WM1's are in use worldwide. It's time tested and the most popular unit of its type. We may be biased, but we really don't think it has any competition. You can pay a lot more and still not get computing SWR or any better accuracy. Many have told us it's the favorite piece of equipment in their station!
Power accuracy 5% of full scale; 10% of reading down to 0.2 full scale. Typically usable even at 1 watt or less on the 20 watt scale. Indicated SWR drops a little at low power, but typically less than 10% at 10 watts and 3:1 SWR. Frequency range is 1.5 - 30 Mhz for full power and accuracy, and usable to 54 MHz, except limited to 100 watts there. (The SWR may read a little high at 54 MHz.. up to 1.3 or so.) Negligible insertion loss. Inline meter is left in line at all times. The unit runs from 8 to 18 VDC at approx. 100-200 ma, most current being drawn by the meter lights. A 115 VAC AC adaptor (wall transformer) is included free. Handsome light-dark grey styling. 6-3/8 x 3-3/4 x 3 inches deep. See the excellent review in Nov. 1989 QST. (We cannot send you the review due to copyright laws. QST sells them.)
COMMENTS ABOUT MODIFICATIONS
Many owners have lengthened the 4 foot remote cable to as long as 30 feet or more. Since the cable carries little current this works fine. However there is a danger of RF being picked up on the cable. This makes the readings inaccurate, and is usually obvious. (The power meter might move backwards, for example.) Although the unit is heavily bypassed,and the cable is shielded, a lengthened remote-head cable may need RF chokes or beads on each wire, including the ground wires in the cable.
This modification is especially popular with those using an amplifier mounted near a tunable antenna, e.g. in the rear of a vehicle. By extending the cable, the RF head can be mounted between the amplifier and antenna, and the main unit mounted at the drivers position to observe SWR. Because the cable is near the grounded vehicle metal chassis in this situation, owners usually have no RF pickup problems.
Some have also asked about extending the range to 3000 watts. This can be done by adjusting the power calibration pot (see WM1 instructions supplied with the unit.) so the unit reads 2/3 of the true reading. However, long key down periods and high SWR's should be avoided since the 1/2 watt 33 ohm resistors in the RF head will be overheated. (We have never seen a case of high power causing a failure of the WM-1 RF head, but 3000 watts is pushing the envelope.)
DISCLAIMER We are providing this information as an aid to owners, but wish to emphasize that we in no way warrant the results.
These items have not been tested and are sold as is.
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