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NM7T OZ Mode Adapter
CW Squeeze Keyer Input Adapter based on the MSK-5
by Brian Kelley, NM7T

MSK5       Karl Fischer, DJ5IL, in his article "All About Squeeze-Keying" (FOC #1980,) coined the name "OZ mode" for the unique keying logic of the MSK-5 Squeeze Key manufactured in the 1970's by the Danish company "Dansk Radio Aktieselskab."  It became very popular in that country and operated in similar fashion to the "Ultimatic" mode of the 1950's except for their touted feature which was intended to further increase sending efficiency by basically inserting a single dit if the dah paddle was first pressed and then the dit paddle was pressed in succession.  After the one dit was formed the keyer would revert back to sending only dahs.  Please read the article for a better explanation and you can also read the original instruction manual for the MSK5 here: http://www.skovholm.com/SK2.pdf .  You will also find instructions on how to operate "OZ" mode [BELOW], which after some practice is actually quite pleasant to use.  To learn more about the history of OZ and other Squeeze Keying modes that have stood the test of time please visit Karl's article at:  http://cq-cq.eu/DJ5IL_rt007.pdf .

The NM7T OZ Mode Adapter
Designed by Brian Kelley, NM7T.  Description and Theory Written by Brian Kelley, NM7T, (Update: 06/15/18)

       The OZ mode adapter is a keying circuit that connects between your paddle and your rig's keyer (or host keyer). It features opto-isolated outputs and full protection of the paddle inputs.  The host keyer must be able to operate in one of the following modes:

       •  Curtis 8044 (mode A w/dot & dash memory)
       •  AccuKeyer (mode B w/dot & dash memory)
       •  Ultimatic (with dot & dash memory)

For Questions and Comments you may contact Brian Kelley, NM7T at:NM7T


OZ Mode Adapter SCHEMATIC:

NM7T OZ Mode Adapter (MSK5 Squeeze Keyer)

PARTS LIST:  (Updated 05/10/2018)

U1 • 74HC14  Hex Inverting Schmitt Trigger
U2 • 74HC75 (or 74HC375)  Quad Bistable Transparent Latch  (Please note manufacture's pinout specs for equivalents!)
U3 • 74HC03  Quad 2-Input NAND Gates with Open-Drain Outputs
U4 • 78L05  +5 Volt Regulator
U5, 6 • 4N35 (or equivalent)  Optocoupler 

Q1 • 2N7000  N-Channel MOSFET

D1, 2 • 1N4148  Small Signal Fast Switching Diode
D3 • LED, 3mm (Optional)
ZD1, 2 • 1N5231B  5.1 Volt Zener Diode

C1 •  0.1 μF         
C2 •  
0.1 - 0.47 μF     
C3 •  10 μF to 100 μF electrolytic
C4 •  0.22 - 1 μF metallized polyester
C5, 6 •  10
nF ceramic type

   Note: Capacitors C1 and C4 should have low dielectric absorption, ie: metallized polyester or metallized polypropylene film dielectric types.

R1 •  15K  Ohm         
R2, 6 •  
10K  Ohm
R3 •  330 to 680 Ohm
R4, 5 •  680 Ohm
R7 •  1.0 M Ohm
R8 - 11 •  1.2 K Ohm
R12 - 13 •  33 K Ohm
RV1 •  100 K Ohm  Linear Potentiometer or Trimmer

   Note: All resistors are 1/4 Watt with 10% tolerance  unless otherwise noted.

OZ Mode Adapter

Shown here is an earlier revision of the NM7T OZ Mode Adapter:::
    Part count is low enough that a mint tin may be considered for housing this project if built compactly.

Circuit Description

      I will refer to the MSK-5 in this documentation even though it applies to the MSK-4 Squeeze Key also.  The MSK-5's main feature was it's "single-dot memory and injection" system.  The NM7T OZ mode adapter provides the "single-dot (pulse) injection" while the host keyer provides the "dot memory."  Although dash memory is not required on the host keyer used with my adapter, it will add the ability to "squeeze" an "A" just as Mode B allows if you release both levers within the first element (dot).

       The MSK-5 Squeeze Key did not allow this.  Another difference is when a squeeze is released within an element.  A good example of this is the letter "P."  Think of a keyer operating in Ultimatic mode with dot memory.  If you release the dash lever before the dot lever (all within the 2nd dash of "P",) the last dot is automatically added.  If the dot lever is released before the dash (all within the 2nd dash), "W" is sent.

       The MSK-5 had just a "single-dot memory,"  so it did not matter if you released the dot lever after the dash (all within the last dash).  The result would be still be a "W".  Because of it's dot memory, the MSK-5 allowed an operator to squeeze an "N" and get off the paddles before the dot was sent, but it could not do the opposite when squeezing an "A" because it did not have any dash memory.

       My OZ mode adapter can provide the same length of squeeze as the MSK-5 Squeeze Key with the added feature of being able to add the last dot in the letters C, P, R in a way that is similar to mode B.  You may be thinking "how can you squeeze an 'A' using the adapter when the host keyer is running mode B?"  The adapter does this by simply cutting off the squeeze at (nearly) the instant the dash lever closes.

       Note:  The dash lever must close within the period of the [dot element plus inter-element space] sent by the host keyer AND upon releasing the "A squeeze" (which must be done within the period of the [dash element] sent by the host) the dot lever must be released before the dash.

        If an "A" is squeezed, gate U3A cuts off the the squeeze by closing gates U3B & U3C.  These two gates can only operate (go LOW) if the output of U3A is HIGH.  At the instant the dash lever closes, the "squeeze" (as we call it) begins, but there is a short delay of ~150 μs between the output of U1C going HIGH and the output of U3A going LOW.  When the output of U3A is LOW, the latch enable (E0,1) input of U2 is also LOW. So prior to U3A going LOW, the latch is in it's transparent mode. At (nearly) the instant U3A goes LOW, U2 latches the state of it's outputs.

       Note:  Only half of U2 is used. The unused half should have it's inputs grounded.

       Prior to the start of the "squeeze", the dot signal (logic level) passes through U3B to optocoupler U5 and out to the host keyer.  With U2 in it's transparent mode, the closed dot lever sets not_Q0 of U2 LOW.  This LOW on not_Q0 initiates the dot pulse which also goes out to the host keyer. (I will cover this section of the adapter further down.)

       Before the dash lever closes, the state of U2's Q1 output is LOW. But with the delay caused by U3A and C4, output Q1 is latched HIGH at (nearly) the instant the dash lever closes.  So, with Q1 latched HIGH and the output of U1D also HIGH, the dash signal is passed through U3D and out optocoupler U6 to the host keyer.  So as long as you have made "the squeeze" quickly AND released the levers in the right sequence, you can squeeze an "A". There is no advantage in having the host operate in Mode A as long as Mode B operates with 100% dot and dash memory.

Karl's MSK-4

The Single Dot (Pulse) Injection Circuit

       When the not_Q0 of U2 goes LOW, the surge in current charging C1 causes a momentary voltage drop across RV1 + R1. The Schmitt trigger inverter, U1A, squares-up this pulse.  MOSFET Q1 pulses the LED in optocoupler U5.  Resistor R7 protects the MOSFET gate from damage when U1 is out of the circuit.  C1 should have very low dielectric absorption for stable pulse generation.  This is why a metallized polypropylene capacitor should be used for C1.  There are only two paddle states in which a dot pulse is fired.  One is when the dash lever is open and the dot lever is pressed.  The other is when the dash lever is already closed and the dot lever is pressed.

       Note:  A dot pulse is NOT generated on a (dash first) release of a squeeze.  U3B passes this dot signal.  The pulse width is adjustable from approx.  1 to 9 ms. When RV1 is set to minimum resistance, the pulse width is ~1 ms.  If your host keyer is not recognizing the injected dot pulse, try increasing the value of R1.  For comparison, at 22 WPM the length of a dot (less inter-element space) is ~54 ms.

The "Squeeze Debouncer"

       The function of C4 is threefold:

       1) It increases the propagation time of U3A when the output switches from HIGH to LOW.  This provides a little extra time for a lever closure to reach the Qn output of U2 before being latched-in.

       2)  It prevents the latch enable input of U2 from bouncing between LOW and HIGH.  Hence the name... "Squeeze Debouncer".

       3)  It gives you a few milliseconds of freedom in releasing both levers at the same time within an element. For example, if you release a squeeze on the second dash of a "K" with the dot lever let off last, you won't get bitten with a "C" if you released the dash lever a few milliseconds prior to the dot lever being released. This window of freedom is ~7 ms with a 1uF cap for C4.

       Note:  If you want an adjustable window of freedom, add a 50K Ohm linear pot in series with R2. This will allow you to set the window as wide as ~41 ms. 

The Simul-Squeeze Test

       If you want to verify your keyer has 100% dot and dash memory on modes A, B, and Ultimatic, perform the following steps:

       1.  Disconnect the paddle from the cable going to the keyer (or build a test cable).  Twist the dit and dah leads together so you can simulate both levers closing at exactly the same time.

       2.  Set your keyer to the lowest possible speed, like 5 WPM.

       3.  Now, emulate a "Simlu-Squeeze" by quickly touching the twisted leads to ground. You should hear just an "A" or an "N". NO "ET", "TE", or mix of A's and N's.

       If you DON'T hear consistent A's or N's on each touch, the mode does not have 100% dot and dash memory.

       If the keyer gives an erratic response, try the following: Use U5 and U6 to isolate the dit and dah paddle lines instead of twisting the leads on your paddle cable. To do this, first add a test point terminal at the cathode of U5 and U6 (pin 2 on the 4N35). Then connect a wire (or "SS Test" switch) between the two terminals. Set the host keyer to the lowest speed and connect your paddle to the input of the OZ adapter.  It does not matter which lever you tap since either will simulate a simul-squeeze!

       Most keyers will give an "A" response to the Simul-Squeeze test. This is because the dot element pulse is (usually) the keyer's timing reference for generating a dash element.  If a keyer responds with an "N" instead of an "A", that is perfectly acceptable since either response will only occur if the levers close within 50 or so microseconds of each other. 

OZ Adapter Technical Specifications

Supply Voltage:   Approx. 8 to 18 Volts DC when using a 78L05 or equivalent 5V regulator.

Note:  If you plan to use a LDO 5V regulator, be sure the output capacitor (Cout) has at least the minimum required capacitance AND it's ESR is within the range specified in the datasheet.  Polarity Protection - Consider "goof-proofing" your build by using a polarity protection diode such as a 1N4001 at [DC IN].
Current Consumption (with R3 = 330 Ohms)
            12.1 mA  (idle)
            17.5 mA  (one lever closed)
            18.1 mA  (both levers closed)

Note:   To lower current consumption, leave LED D3 out of the circuit or add a switch to disable it. If you plan to dedicate the adapter circuit to your keyer, you can reduced the current consumption even more by leaving out the optocouplers. Be sure to ground the unused inputs of U1 and U2.

Paddle Voltage:    ~4.3 Volts

Paddle Current:    ~130 μA each

Optocoupler output sink current:  ~5 mA max.

Note:   Paddle inputs are protected from ESD, RFI and any accidental connection of DC supply voltages. Capacitors C5 and C6 along with the hysteresis provided by U1B and U1C eliminate any paddle contact bounce.  U1 and U2 - Consider adding decoupling caps (0.1 μF) between the Vcc and Gnd pins.


Mode A and B Variants

       Some keyers don't have dot and dash memory when operating in mode A. Without dot memory, the host keyer will usually miss the ~5 ms dot pulse when an "N", "K" or "Y" is squeezed at low speeds.  Some keyers (notably Logikey's V0 mode) have a modified mode B. V0 mode disables the dot memory during the first third of the dash.  This lowers the chance of accidentally sending an "R" when an "A" is squeezed. But if used as the host keyer, it can cause an "M" to be sent when trying to squeeze a "K".

       The K1EL keyers have an adjustable memory "window" when operating in mode B. It works like V0 mode in the default setting.  Having the OZ mode adapter's dot injection "window" reduced may cause errors in your sending. For example, you might hear a "T" go out when trying to squeeze an "N".

Ultimatic Mode Variants

       The original Ultimatic keyer was built by John Kaye, W6SRY, in 1953. It used a single-lever paddle. In 1955, John created the twin-paddle Ultimatic keyer which ALSO had dot and dash memory. I bet you know were I'm headed with this. Most modern keyers include an Ultimatic mode, but it may be really "sub-ultimate" if it does not include dot and dash memory.

       Then there are dot preferred and dash preferred Ultimatic modes. If dot preferred is used, you will have a hard time trying to insert a dash  while holding the dot lever closed. With dash preferred, you will be lucky if you can insert a single dot! Obviously, these two modes must not be set on the host keyer.

The GK-1 Golden Key Keyer
Golden Key        The GK-1 Golden Key was made in Helsinki, Finland by EW-line (1) and was a copy of the Autronic MK-1 keyer. (2)  The Autronic MK-1 was one of the first keyers (if not the first) that operated in Ultimatic mode with dot-preferred timing. (3) The GK-1 was initially only available in kit form. (2) The GK-1 was produced from 1967 to 1974. (1)  The MK-1 was always advertised with the Autronic single-lever paddle, but it could also be used with a twin-lever paddle. (4)  Matti Käki, OH2BIO, webpage with a photo of the GK-1 Golden Key sitting above his Collins 75S-3B. (5) There are a number of keyers out now that offer the Ultimatic mode with the option of dot preferred or dash preferred.  One notable keyer is the JUMA KEYER1.  It offers Basic iambic mode (default) or Golden Key mode (Ultimatic mode w/dot priority). (6)


1)  EW-Line (Helsinki, Finland) built the GK-1.  EW-Line was founded by Reijo R. Laine,  OH2EW. He was a pioneer in component and HiFi equipment selling in Helsinki in the 60's and 70's. The GK-1 Golden Key was produced from 1967 to 1974.  The GK-1 at the the Radio Museum.

2)  The Autronic MK-1 electronic keyer page at the Radio Museum.  https://www.radiomuseum.org/r/electrophy_autronic_keyer.html

      In a email, OH6NT Thomas wrote... "The Autronic schematic was copied in 1965 by OH2EW Reijo and OH2QV Anssi."  OH6NT has a very large collection of keys and paddles (and some keyers) at: http://www.tronico.fi/OH6NT/keys.htm  Reijo owned the Hi-Fi import company EW-line. In 1967 the first Golden Key (kit) was sold. EW-line later came out with the GK-1 Mk II.

       By coincidence, my first paddle was an Autronic. As I recall, it was about $80 in late 1967.  (bk)

3)     If the GK-1 Golden Key circuit was copied from the Autronic MK-1, then the Autronic operated in dot preferred Ultimatic mode.      

4)     The Autronic paddle and keyer was first advertised in the June, 1960 issue of QST. http://www.qsl.net/n6tt/keyerpad.html#auto

5)      http://www.mattikaki.fi/hobbies/1971.htm

6)      The JUMA-KEYER1 webpage. (Note: Mode A does not have dot & dash memory) http://www.jumaradio.com/juma-keyer1/

7)      The Simple CW Keyer (elbug) of Matti Hohtola, OH7SV. This keyer has the same keying logic as the GK-1 Golden Key.
          http://www.saunalahti.fi/hohtola/ham/elbug/oh7sv-elbug.htm    Email:   matti.hohtola@saunalahti.fi

The Finnish GK-1   The Finnish GK-1


OZ Mode is pretty easy to learn, and if you know how to use Ultimatic Mode then you are almost there.  We must assume here that you already own a dual-lever paddle of some sort and have general CW experience.  Click image below for full-sized version:

OZ Mode Squeeze Keying Chart 

Click here for the PDF:  CW_Dual_Paddle_Squeeze_Keying_Chart_for_MSK5_OZ_Mode.pdf

Edited: 06/15/18
©2018 Copyright - Michael A. Maynard