MARCONI Wavemeter
TYPE M.P.4; P.S. No 2170A
Inst. No 327042
Marconi's Wireless Telegraph Co Ltd London

The M. P. 4 buzzer's two windings (similar to those found in modern earphones) are used to actuate the buzzer contacts, and there is an additional (what appears to be a) small induction coil below it on the side recessed somewhat in the Bakelite base. This third coil has two small, semicircular (what appear to be) magnetic pole pieces surrounding the winding. The buzzer is attached to the door at a haphazard angle that necessitated the constructor's providing a little notch in the interior wall of the front panel in order to provide sufficient clearance to completely close the door. So this wavemeter may have been reworked to function experimentally as a signal generator. There is no evidence of its ever having been fitted with a detector nor provision for any indicator light or meter. Curious.

I've not disassembled the wavemeter, so I can't be too specific about its internals, but it seems to be a variable condenser housed in a sealed wooden compartment at the rear. I say that, because I do not find continuity between the wires exiting that compartment as would be normal for a veriometer. The shaft of the knob goes through the front panel, and past what appears to be an RF transformer into the rear sealed compartment. Although there don't seem to be any hard stops at the ends of the scale, there is some binding that prevents moving the pointer much past the bounds of the dial legend without applying more than light force. The transformer (if indeed that is what it is) seems to be close-wound, mauve colored, cotton covered, perhaps number 28 gage wire on a black plastic/Bakelite dowel about 1/2" in diameter and 4" long. there are some small white numbers (DWO8354) painted on the end of the coil-form, but It's difficult to be exactly sure of the circuit, as some of the wires are detached.   Here's an incomplete wiring diagram:

Marconi Wavemeter MP4 Schematic

The fellow I got it from gives his address as "Norwich, Norfolk," and says he got it from a neighbor who constructed a TV set from a green radar CRT after the war.

The wavemeter is an interesting piece. It does resemble the Townsend wavemeters, shown on the Oxford web site, in its use of a buzzer, but the construction of the cabinet and fittings seem to differ to some extent. The Townsends shown here and here use a different style of clasp for the little door, and the door's ends are capped with cross-grain pieces. The door of the M. P. 4 wavemeter uses small cross-grain splines instead, but the two little dark marks on the inside of the door are present. The buzzer seems to be quite similar in design, but not identical. Both buzzers are attached to an inclined Bakelite base, but some details differ.

I am grateful for any insight into the age, function, or intended use for this specific unit.  To date I have received the following hints:

"... estimate by its tag that it would be from the early 1920's and
used at commercial shipboard or land stations. The dial is
reminiscent of the Type 11 Radio Direction Finder, which dates
from 1919 - 1926."

[

Photograph of 'Marconi' Direction Finder Type 11F, by Marconi Company, London, c. 1920.  For details click here.

While the dial appears to be made of metal, the nameplate is very similar to that of the M.P.4 wavemeter.]

"The identification plate is the giveaway which is typical 1920's,
Marconi were still using components such as the rotary lock as
late as the 1930's on military items supplied to British army
simply because it was cheaper than designing something to replace
it which would be no better, they were still using the Marconi V2
intervalve transformer in aircraft sets during WW2."

			Wavemeter Face: The dial face of this wavemeter is marked 7 through 8.  I'm guessing that is probably the resonant wavelength in meters:         70 meters = 4.28 MHz         80 meters = 3.75 MHz However, it is possible it is marked in MHz:         7 MHz = 42.83 meters         8 MHZ = 37.47 meters
			Legend Plate: Because the 'Marconi's Wireless Telegraph Co. Ltd., London ' ledgand appears on this instrument, it places the date of its manufactur after March 1900.
			Interior of Cabinet: The tuning shaft, switch, and end of the transformer are seen in this view.
			Transformer Legend: It is possible to read the legend on the end of the transformer in this view.  To me it appears to be: 'DWO8354.'
			Buzzer Rear: Here is a view of the buzzer used to create the radio waves.  Note that the buzzer seems to have been haphazardly mounted and necessitated a notch in the cabinet wall to permit closing the lid.
			Buzzer Right Side: The windings that operate the buzzer by attracting the iron armature are seen in this view.  In the foreground is seen the "induction coil, " if that is indeed what it is, that apparently generates the radio waves.
			Buzzer Detail: This close-up provides more detail than the previous image.
			Buzzer Left Side: The windings that operate the buzzer by attracting the iron armature are seen in this view.
			Dial Scale: This close-up provides a view of the beveled pointer and ivorine (a substance resembling elephant tusks in color and texture) dial scale, and gives an indication of the general quality of workmanship.
			Latch Detail: This close-up shows the unique early cabinet latch used by Marconi's Wireless Telegraph Co. Ltd.
			Switch Knob and Legend: This close-up provides a view of the metal switch knob and ivorine (a substance resembling elephant tusks in color and texture) legend plate
			Power Plug: Apparently this is where the buzzer got its power.
			Power Plug Detail: This close-up shows the power input terminals.
			Last Edit: January 12, 2011
			Contact: © Copyright L. Dighera 2007 - 2011, All Rights Reserved