Path: Home > Rockwell Collins KWM-380 > KWM-380 Notes

My personal KWM-380 notes - some fact / some opinion - but always accurate (hihi):


Pros:

  • Very stable - PLL synthesizer - a bit bizarre - two reference frequency (39.6 Mhz. & 455 Khz.) scheme...
  • Accurately reads out to 10 Hz.
  • General coverage (0.5 to 29.999 Mhz.) - double conversion, superhetrodyne receiver...
  • Continuous tuning (NO bandswitching - receive & transmit) - a real breakthrough at the time...
  • Four speed - push button tuning (choice of 1 Mhz., 1 Khz., 100 Hz., or 10 Hz. steps)...
  • I.F. passband tuning...
  • Easy to read BIG (0.56" high) red LED display...
  • Excellent SSB & CW AGC action - no need to modify (as required on most older Collins receivers)...
  • No need for a separate or remote VFO (the "norm" at the time for split operation) has separate A/B digital VFO...
  • Big heat sink - quiet operation - no fans required for SSB & CW use...
  • 100 watt output transmitter...
  • Excellent, well regulated 14 VDC linear power supply is built in...
  • Operates on either 105-125 VAC or 210-250 VAC 50/60 Hz. or can be optionally powered from a 12 - 15 VDC source...
  • Really slick memory & VFO operation with optional Kiron board & optional keypad - another breakthrough at the time...
  • Fairly easy to work on...
  • Looks great next to my Hammond HL-2000A amplifier (same vintage)...
  • Really holds it's value on the used market (not many manufactured - my best guesstimate - less than 2,500)...

Cons:

  • SSB filter is too narrow - 2.1 Khz. bandwidth filter...
  • Surprisingly the I.F. filters are NOT Collins mechanical filters! However, they are very high quality crystal filters manufactured by Piezo Technology Inc.
  • Bizarre passband tuning I.F. frequency - filters are at 6.255 Khz. (can't get those at INRAD)...
  • Restricted receive & transmit audio (receive audio can be improved with careful use of passband tuning). Spec. is 300 to 2400 Hz.
  • Stock AM filter is too wide (8+ Khz) - actually not a filter (it's an LC circuit). 5 Khz. audio beat easily heard when tuning around the SW bands. Nearly impossible to find AM filter (6 Khz.) option...but NICE if you can find it...
  • No R.I.T. - not as big a problem these days - as most folks dead zero beat...but rough when working older rigs. This can be worked around by using the two VFO s but very awkward...
  • No AM transmit (however, great AM receive)...
  • Not overly sensitive - no receive R.F. amplifier - passive front end into a mixer. This is perfect on the 160 - 40 Meter bands but not so on 20 - 10 Meters. Spec. is 0.5 uV or better for 10 dB (s+n)/n...
  • Stock S-meter setting is very stingy. Per service manual: S9 = 100 uv (can be adjusted however)!
  • Generally overpriced on the used market. As I write this (2008) you can purchase a brand new Yaesu FT-2000 or Icom IC-756 ProIII for the average price a good KWM-380 goes for on the used market. However, if you are a Collins fan - it's simply a "must have"...

Maximum Transmit Audio Response Test

Notes to table below:

  • Careful attention was made to make sure no ALC was ever engaged during testing at any frequency.
  • Digital readout Kenwood signal generator used for accuracy - directly fed into the rear panel audio input RCA jack.
  • Some audio pre-emphasis (under 3 db) is built into the KWM-380 - peaking around 1,720 Hz. This was ignored as I was concerned with low & high end point roll off.
Roll Off
(vs. 1 Khz.
Reference 0 db)
Low Frequency
High Frequency
-3 db
380 Hz.
2.43 Khz.
-6 db
320 Hz.
2.53 Khz.
-9 db
280 Hz.
2.60 Khz.
-12 db
253 Hz.
2.63 Khz.

Pretty much all energy is gone at 150 Hz. (low end) and 2.77 Khz. (high end).

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