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Mizuho MX-7S HF SSB 7 MHz HT Handheld Transceiver User Manual Service Manual
Tokyo Hy-Power HT-750 HF SSB HT Handheld Transceiver for 7 MHz 21 MHz 50 MHz User Manual Service Manual
|This article provides educational and reference information on the
Kachina MP-25 and Scientific Radio Systems SR-MP-25 HF SSB Manpack Transceiver
*** RADIO COLLECTORS INFORMATION *** NOT FOR SALE *** FOR REFERENCE ONLY ***
[Note: Kachina Communications, Inc. made the MP-25. Kachina Communications, Inc. closed its HF equipment business in May 2001.]
[Under private label, Kachina Communications supplied SR-MP-25 to
Scientific Radio Systems, Inc. which went out of business in Sept 1997.]
[A typical MP-25 set sold new for approximately US$5000 to
US$8000, depending upon which accessories and options were in the
The Kachina MP-25 is a manpack type transceiver which may be
used for portable, pedestrian mobile, vehicle mobile, or fixed
installations. The transceiver is designed to receive and transmit SSB
single sideband suppressed carrier (2R7J3E), semi-break-in CW telegraphy
(350A1A), and compatible amplitude modulation (2R7A3E) signals. AM is
received as USB.
Frequency coverage is 2000.0 kHz to 14999.9 kHz in 0.1 kHz digital steps
using front panel rotary switches. The MP-25 is designed to operate over
the temperature range -30C to +55C and is fully waterproof to 1 meter.
The transceiver features an internal simplified manual antenna tuner
with a locking rotary whip antenna mount and standard 3/8"-24 threaded
fittings. Antenna connections include push-on posts for random wire
attachment and BNC connector for mobile or dipole antennas. The front
panel has a waterproof speaker with on/off switch for monitoring. A
companion 12V power supply / battery charger for base station operation
also provides an external speaker for clear crisp reception of voice.
Operation and Maintenance Manual (Service Manual)
MP-25 Standard Features
• Digital frequency selection with tactile rotary switch knobs
• Built-in antenna tuner for whip, random wire, or dipole
• Integral rechargeable battery pack (NiCd or SLA)
• Long term operation on battery due to low receive power consumption <200mA
• Multi-mode operation - USB, LSB, compatible AM, semi break-in CW, compatible with external modems
• High/low power selector (25 Watt / 6 Watt transmitter output)
• Internal waterproof front panel speaker
• Uses standard military manpack accessories and audio U-229 connectors
• Integral swivel antenna mount for whip antenna
• Audible low battery indicator when pack needs recharging
• Dependable hardware logic ICs - no vulnerable software or microprocessors
• Uses standard 12 VDC for vehicle power and internal battery
• Battery voltage, S-meter, and SWR meter
Promotional Sales Brochure (for reference only)
Kachina MP-25 Brochure
(2MB pdf file)
Promotional pamphlet with accessories, configurations, options, pricing,
maintenance packages, and other factory sales information.
[Kachina closed its HF business in 2001]
FOR REFERENCE ONLY
NOT FOR SALE
The following accessories were available from the factory:
|• MP-25-HS2 Handset [a]- H-189/GR miniature military handset. Fully Waterproof. Dynamic, 150 ohm
impedance.Weight .51 kg.
• MP-25-HG Hand Generator [h]- Designed to operate the MP-25 Transceiver
and simultaneously charge the batteries. Batteries must be in place when
operating the generator. Weight 2.0 kg.
• MP-25-CB Carrying Bag [e]- Manufactured of nylon, the bag not only
protects the transceiver, but, also provides pockets for the various
accessories such as the microphone, folded whip antenna and other
antenna accessories. Fitted with adjustable padded straps. Available in
olive drab or green camouflage pattern. Weight 0.63 kg.
|• MP-25-AD Dipole Antenna [c]- This center fed dipole is
wound on high impact plastic spools. A calibration chart is provided to
show turns to be removed from the spools. Final adjustment is made using
the MP-25 built-in SWR bridge. Antenna is provided with 10 meters of
RG58-U coaxial cable. The dipole antenna may also be used as a longwire
antenna. One section of the antenna is used as a ground plane. Weight 1.3 kg.
• KC-SP-1 Solar Power Unit [i]-
Allows transceiver batteries to be charged from the sun. Fitted with
meter so that the collector may be positioned for maximum charge Limited
availability. Weight 1.94 kg.
• MP-25-PSC Power Supply/Charger [g]- Powers the radio in base station
operation or charges one battery pack, either sealed lead acid or nickel
cadmium. A front panel switch converts the base station power supply to
a battery charger allowing the battery to be charged while attached to
the transceiver. The supply allows operation from 110/220 volts, 50 or
60 Hz. A fuse and current limiting cut-out protect the power supply
against short circuits. The supply is electronically regulated and
current limited, and the output is over voltage protected. Contains
built-in loud speaker for improved audio during base station operation
of MP-25 Transceiver. Weight 3.65 kg.
• MP-25-AW Folding Whip Antenna [b]-
Made of fiberglass. Collapsible and may be stored in carrying bag.
Connects automatically when fitted to transceiver. Antenna may be
rotated to any angle with respect to the transceiver and locked in
place. Weight 0.39 kg.
• MP-25-MB Mobile Mounting Bracket [f]- Heavy duty type, clamps around body of transceiver, allowing a strong attachment to the vehicle. Weight 1.12 kg.
• MP-25-MC Hand Microphone [j]- Military type M-80/U, rugged, dynamic type
microphone. Used when transceiver is operated with the MP-25-PSC power
supply speaker in base station operation. Weight 0.39 kg.
|• MP-25-BP(NCE) Nickel Cadmium Battery Pack [d]- Clips on the rear of
transceiver. If nickel cadmium batteries are not fully discharged they
will develop a memory for the lower charge. Unlike sealed lead acid
batteries, they should not be trickle charged. Their regulation is
superior to that of the lead acid types.
• MP-25-BP(LAE) Sealed Lead Acid Battery Pack [d]- Consists of two 6 amp
hour, 6 volt, rechargeable, sealed, lead acid batteries in protective
box. Clips on to rear of transceiver. Unlike nickel cadmium batteries,
sealed lead acid batteries need not be deep discharged. Regulation
inferior to nickel cadmium type.
• MP-25-CW Telegraph Key - May be positioned on senders knee or operated on a table or other surface.
• MP-25-HP1 Headphones - Military type H140/BU. Weight .69 kg.
• PN980014 Mobile D.C. Power Cord - Allows the transceiver to be operated from a vehicle battery.
• MP-25-MW1 Mobile Whip Antenna - Stainless steel antenna approximately 2.5 meters long (9 Ft.). Weight 2.2 kg
• MP-25-BL Ball Mount - For attaching the MP-25-A Wl Mobile Whip Antenna to the vehicle.
• MP-25-S2 Heavy Duty Spring - designed to be used with the MP-25-BL Ball Mount and the MP-25-A Wl
Mobile Whip antenna. Helps prevent antenna damage.
• MP-25-CH Battery Charger [g]- Similar to MP-25-PSC(E) above but allows
the simultaneous charging of 4 battery packs, either sealed lead acid or
nickel cadmium. Will operate from 110/220 volts, 50 or 60 Hz.
• PN980013 Extender Board Kit- A set of extender boards that allow
printed circuit modules to be extended above the transceiver for
maintenance and service.
• Power Source: External 12 volt supply, negative ground only.
• Frequency Range: 2000.0 kHz - 14999.9 kHz in 100 Hz steps USB LSB CW AM
• Modes: 2R7A1A (USB & LSB), 350A1A (CW), 2R7A3E (compatible AM).
• Operating Temperature Range: -30 C to +55 C.
• Waterproofing: Immersion to 1 meter (20 C).
• Size: (W X DX H) 32 X 34 X 11.5 cm.
• Weight, without batteries: 4.3 kg (9.6 lbs.).
• Weight, with sealed lead acid battery pack: 7.25 kg (16.1 lbs).
• Weight, with nickel cadmium battery pack: 7.29 kg (16.2 lbs.).
• Metering: Relative received signal strength. Relative transmitter
power output. Reflected power (TUNE mode). Battery voltage.
• Antenna Tuner: Built-in. Capable of matching to whip or longwire
antennas from 2 - 150 meters in length. Special provision to match
• Lighting: Spring loaded switch activates readout display for
approximately 10 seconds. Meter illuminated while switch held on. Meter
illuminated when mode switch in TUNE position.
• Memory: Frequency change may be entered only when readout display is
illuminated. Last four digits of second frequency may be switch
programmed in readiness for a change. Will not activate until READ
switch is activated.
• Out-of-Lock Indicator: Audio tone warns if synthesizer out-of-lock,
such as when large changes in frequency are made or battery needs
• The MP-25(E) battery pack clips on the transceiver without having to withdraw the transceiver from the case.
• The MP-25 uses either rechargeable sealed lead acid or nickel cadmium battery packs.
• Optional connecting leads allow the transceiver to operate from an external 12 volt DC source.
• Signal to noise: Better than 10dB for 0.5uV input signal.
• Sensitivity: More than 0.125 watts output for 0.5uV input signal.
• AGC: Less than 10dB variation in audio output from 5uV to 0.1 V input signal.
• IF Rejection: 2 - 9.9 MHz Better than -90dB ; 9.9 - 15 MHz Better than -60dB
• Image Rejection: Better than -90dB.
• Internal Spurious Signals: Not greater than the equivalent of .5uV except at 5 MHz= 3uV.
• Audio Output: I watt minimum with not more than I 0% distortion.
• Clarifier: +/-50 Hz minimum.
• Current drain (readout display off, volume low): Typically 170mA.
• Current drain (readout display on, volume low): Typically 200mA.
• Current drain (readout display off, volume normal listening level): Typically 185mA.
» Note: All measurements based upon 12.6 volt D. C. input voltage.
• Power Output: SSB - 25W P-P average. 20W minimum. (low power 6W P-P average)
• CW - 10W (internally adjustable).
• AM - 6W (carrier).
• Intermodulation distortion: Not less than -26dB at 20 watts. Typically -30dB at 25 watts.
• Spurious Output: -50dB with reference to 25W level.
• Harmonic Suppression (50 ohm output): -40dB.
• Carrier Suppression: -40dB minimum.
• Frequency Stability: +/-100 Hz from -10C to +50C ; +/-150 Hz from -30C to +55C
• ALC: Limits output power to within 1dB of setting.
• Current Drain: Average voice: 1 ~ 2 amps. / CW (Key down):
4 amps. / CW (Average): 1 ~ 2 amps. / AM: 1.5 amps.
• Microphone: H189/GR or equivalent.
» Note: All measurements based upon 12.6 volt D. C. input voltage.
[Editor's note: the above information was provided by the Kachina MP-25 Operation & Maintenance Manual]
Scientific Radio Systems SR-MP-25 transceiver, SR-MP-25-PSC power supply, J-38-style key, M-80 microphone, Super Antenna MP1 SuperWhip ruggedized manpack antenna.
After these types of HF radios are removed from commercial
and military service, some find their way into the surplus market,
to be eventually acquired by ham radio operators, shortwave listeners, or radio collectors.
The MP-25 transceiver is designed for short, medium and long path
communications work. The transceiver will operate from a whip, longwire
or dipole antenna. A built-in antenna coupler allows proper coupling to
the whip and longwire antennas. Typical system application is given
below. [source: Kachina]
||MP-25-BP Battery Pack
||MP-25-BP Battery Pack
||Moving or Stationary Comms.
||MP-25-PSC(E) Power Supply
||Normal Base Station Service
Kachina MP-25 Images
Kachina MP-25 second version transceiver with second version MP-25-CH power supply charger (photo courtesy of teotwaki)
Photo: Kachina MP-25 top view showing second version battery pack and enclosure (photo courtesy of teotwaki)
Photo: Kachina MP-25 whip antenna (photo courtesy of teotwaki)
Photo: Kachina MP-25 second version battery pack (photo courtesy of teotwaki)
Photo: Kachina MP-25 first version battery connections - Kachina MP-25 first version battery pack
Photo: Kachina MP-25 Tuning Instructions card (photo courtesy of teotwaki)
Photo: Kachina MP-25 Antenna Instructions card (photo courtesy of teotwaki)
Antenna Tuner Operation
The internal antenna tuner is capable of
tuning and matching any HF antenna of any type encountered in the field
or base station operations. In the Tune mode, the transmitter transmits a
low power level CW carrier for tuning purposes. The Antenna Tuner is
adjusted using the Tune mode by tuning ④ ANT.TUNE lower knob (capacitor) and ⑤
ANT.TUNE top rotary switch (inductor) for lowest reading on the meter,
indicated by the green color. If SWR is in the red, check antenna or
|Kachina MP-25 SWR Tune Meter Color Code
|1.0 to 2.0
|2.0 to 3.0
| 3.0 or higher
|Note: SWR levels are approximate
Procedure for Tuning a Whip or Random Wire Antenna
1. Set the ④ ANT.TUNE lower knob to the 2 position.
2. Set the ⑤ ANT.TUNE top rotary switch to the 22 position.
3. Set the PORT/MOB switch to the PORT position.
4. Switch to TUNE mode.
5. Rotate the ⑤ ANT.TUNE top rotary switch counter clockwise, stopping at the lowest reading on the SWR meter.
6. Rotate the ④ ANT.TUNE lower knob, stopping at the lowest reading on the SWR meter.
7. Repeat steps 4 and 5 above sequentially for lowest reading on the SWR meter.
8. Return to USB mode.
Bypass the Antenna Tuner
For use with 50 ohm BNC external antenna such as resonant dipole or broadband dipole.
1. Set the ④
ANT.TUNE lower knob fully counter-clockwise to the 0
2. Set the ⑤
ANT.TUNE top rotary switch to the 23
bottom vertical line position.
3. Set the PORT/MOB switch to the PORT
(see photo at right)
The PORT/MOB switch should normally start in the PORT position for most
antennas. This includes 50 ohm antennas, dipoles, random wires, and the
manpack whip antenna. It may be put in the MOB position for tuning
some mobile antennas or fixed station antennas which are connected via
the DIPOLE connector (BNC) or it may be needed to achieve an acceptable green SWR
some other types of antennas at lower frequencies (2MHz to 8MHz). In
the MOB position, an additional shunt capacitor of 750 pF is applied to
PI-network antenna tuner on the transmitter side, which is especially
helpful for tuning the lowest frequencies, but MOB position is usually
detrimental to tuning at higher
For more information see Antenna Tuner Instructions Cards
Whip Antenna Mount
The rotating whip antenna mount on the right side of the faceplate is
suitable for lightweight whip antennas in field portable operation. When
using a mobile or fixed antenna connected to the DIPOLE (BNC) connector
or the antenna push terminals, the whip antenna and its hardware should
be completely removed from the mount, to avoid RFI, noise problems, and
detuning of the intended external antenna system.
Using Whip Antennas
The Kachina model MP-25-AW Folding Whip Antenna is a lightweight
collapsible fiberglass whip, originally supplied with the MP-25. The
standard military manpack metal AT-271 collapsible whip was supplied
with later versions, along with 3/8"-24 fittings which interlock with
the quick-disconnect fitting of the mount. Care should be taken to avoid
extreme angular shock or leverage on the whip mount
while operating /Pedestrian Mobile with heavy or long whips such as the
AT-271. After-market antennas with integral loading coils, such as the Super Antennas MP-1
provide greatly increased efficiency (+5dB or more) over the stock
whip, and are highly recommended for use with the MP-25. When operating
portable or /Pedestrian Mobile with any whip antenna, a single insulated
wire counterpoise should be attached to the push terminal ground
connection of the MP-25. The counterpoise wire may be a random length or
may be cut somewhat shorter than a quarter wavelength at the desired
optimum frequency. In practice, 4 lengths of counterpoise wires have
been found to be suitably optimum for the entire operating range of the
MP-25, when most of the wire is deployed on the surface of earth ground
Recommended MP-25 field counterpoise wire length
|2MHz to 3.4MHz
|3.5MHz to 5.9MHz
|6MHz to 8.9MHz
|9MHz to 14.9MHz
after-market pre-tuned teflon wire portable counterpoise radial sets
which are suitable for MP-25 and other manpacks in the field. See SuperWire Stealth Radial Sets MR4020, MR8060, MR4010, MR8075
Kachina MP-25 Antenna Tuner
Settings for 50 ohm
Audio Connector Pinout
|Microphone, Speaker, Handset, Headset, CW Key
The audio and accessories connector is a U-283 (the 6 pin version of the
common 5 pin U183 military audio panel connector) and it is compatible
with most 5 pin standard U-229 microphones, handsets, headsets,
speakers, etc. The MP-25 does not output microphone sidetone to the handset speaker audio.
Modems, Devices, Repeaters, and +12V Accessories
A variety of interconnect devices may be used to expand or interface
with the transceiver. When setting up equipment, observe proper
compatibility procedures, especially pin signals and voltage limits for
gear using center pin features. The +12V pin is capable of delivering
several amperes, limited by the internal circuit breaker, dependent upon
how much total current is used for transmit.
attaching an accessory that has a U-329 plug (6 pin military connector)
beware that there is +12VDC on center pin F.
The center pin is direct +DC supply from the radio battery and is controlled by the radio on
DO NOT CONNECT a 6 pin MUX or FILL device to the MP-25!
Pin out of Kachina MP-25 front panel
audio connectors type U-283
(compatible with U-229 or U-329 accessories)
Standard military H-189 and H-250 handsets, and M-80 microphones are compatible with
the MP-25. The M-80 seems to have the most punch for excellent transmit audio.
Many other types of standard military audio U-229
accessories, such as intercoms, handsets, and headsets work well with
the MP-25. The microphone input circuit has an impedance of
approximately 1k ohm, and is suitable for low impedance dynamic
microphones and audio equipment in the range of 50 ohms to 1 k ohms (50,
150, 600, 1k, etc). Both front panel audio connectors are
identically connected in parallel and may be used
Photo: Typical MP-25 compatible handsets H-250, H189, and M-80 microphone using standard military U-229 connector
|A manual CW key may be attached, connected from pin E to pin A of the
U-229 (or U-329) connector. The CW frequency is offset +800Hz (0.8kHz)
display frequency. In CW mode, the radio operates Upper Sideband, and is
suitable for crossmode operation with stations using Upper Sideband
(USB) voice. To zero beat with another CW station, align the display
frequency to match the received tone of the CW sidetone pitch. In other
words, when the other station's CW signal sounds like it is at the same
pitch as the MP-25 CW sidetone, it is the correct zero beat frequency.
is no special narrow CW filter, it uses the standard USB 2.7 kHz filter.
The logic level HI of the CW pin is +12V, and ground to send. If using a
bug key or an external electronic keyer, be advised that the
CW circuitry is rated at 35 WPM morse code maximum, and the transmitted
dits may be clipped if that speed is exceeded. The default keying is
semi-break-in, which has a fairly fast fixed time delay. It is normal to
encounter some chirp on the transmitted CW when using semi-break-in at
each initial key-down pulse interval. To reduce the chirp, hold down the
microphone PTT while sending a CW transmission. Microphone audio is
muted from the transmitter when mode switch is in the CW position.
CW key wiring of
U-229 female cable connector pin out
|CW transmit frequency is offset 0.8kHz above display frequency.
Examples of Kachina MP-25 display frequency to CW zero beat conversion for common ham radio and HFpack CW calling frequencies
|SET DISPLAY FREQUENCY|
|ACTUAL CW TRANSMIT FREQUENCY |
Photo: Typical CW key with U-229
A computer sound device or external modem with audio and PTT interface
may be attached to the front panel connectors. When transmitting with a
modem, the BAT.READ/LOW PWR switch should be placed in the LOW PWR
position, to avoid overheating due to continuous duty power output. The
shows connection of a computer sound device modem to computer earphone
output, microphone input, and a simple PTT interface to a serial port
made with a
transistor and 2 resistors. Most standard computer-radio interfaces may
be wired similarly. The normal logic level of the PTT pin is +12V, and
ground 0V to transmit. It is suitable to be driven by either open
collector or relay closure. It is not suitable for direct 5V, 3V, or
1.8V logic connection (use an open collector buffer instead).
Image: Connection schematic diagram of U-229 female cable connector for computer sound device modem
External Speaker and Power Supply / Charger
The power supply and charger MP-25-PSC (first version) or MP-25-CH
(second version) has a good sounding external speaker in it. It is a
linear supply providing OPERATION for the transceiver and CHARGE for the
battery. The power supply plugs into the front panel J903 connector, and provides +12VDC nominal from selectable 115
VAC or 220 VAC mains.
It is recommended that the battery be either
removed from the radio while charging, or else all the panel clamps be
loosened, to prevent volatile gas (hydrogen / oxygen) build-up inside the sealed radio
enclosure. The power supply OPERATE/CHARGE switch must never be in the
OPERATE position while the battery is connected in the radio. The battery may be charged while installed in the radio. Charging Battery Reminder: always loosen the 6
clamps of the manpack case cover while charging, and slightly let the
cover separate from the front panel gasket, to release the hydrogen and
oxygen gas. The
OPERATE/CHARGE switch must only be set to CHARGE while the battery is installed and
attached in the radio. There is a separate charge cable which may be
plugged into the battery for charging it externally while the radio is
operated. For the NiCad battery, the charger power should be turned off when the battery is fully charged (about 13.8 to 14.0 VDC).
Keep in mind that the front panel volt meter is intended only for a
rough check of battery voltage. The front panel meter is not accurately
calibrated enough to determine full charge voltage. So, a separate
calibrated voltmeter should be attached to Pin F of the audio connector
to test the voltage, and determine meter error so that it can better be
utilized as a charge indicator.
The SPEAKER/ON switch on the front panel of the transceiver
controls both the internal speaker and the power supply speaker, it does
not mute the receive audio ported through the front panel audio
connectors. Other types of military loudspeakers with standard U-229
connectors may be additionally attached to either front panel audio
Photo: Kachina MP-25-PSC Power Supply / Charger Speaker first
version (Scientific Radio Systems SR-MP-25-PSC) and compatible LS-454
Photo: Front panel power connector J903 pinout (A=Ground | B=+12VDC | C=Speaker)
Power Connector Plug Family Type = MIL-DTL-26482 (shell size 8, standard insert, 3 pin, cylindrical connector)
Radio Panel Power Female Connector = Type MS3114 (Jam Nut). Amphenol Part # SP07A-8-3S or PT07A-8-3S
Supply Cable Power Male Connector = Amphenol Part # SP06A-8-3P or PT06A-8-3P or SP06A-8-3P(SR)
Power Connector Plug Family Type = MIL-DTL-26482 (shell size 8, standard insert, 3 pin, circular connector)
Kachina MP-25 Timer Mod
The frequency display timer on the stock MP-25 is about 15 seconds, and
it is a little too quick for most users to tune in a station. This
modification increases the display illumination and setting time to
about 35 seconds.
Kachina MP-25 Display Timer Mod Instructions and Diagrams
This mod requires one part: a 4.7uF capacitor.
The capacitor may be electrolytic, tantalum, or non-polarized rated at +9VDC.
These instructions show a surface mount capacitor.
1. Remove enclosure, battery, and internal top cover. Remove internal shield plate which covers module PC501.
2. Extract PC501 module board. Pry it out evenly of the socket by levering a small screwdriver into the holes on each edge.
3. Locate C514.
4. Solder the 4.7uF capacitor across the exposed leads of C514.
5. Replace the module, plate, cover, and enclosure.
6. Mod is complete. Test it by turning on the radio and observing the display illumination time.
Image: Kachina MP-25 Display Timer Mod Instructions and Photos
Image: Schematic of Kachina MP-25 Display Timer Mod
Kachina MP-25 Output Power Mod
|The MP-25 amplifier board final transistors are
capable of much more
than 25 Watts output power (each of the two transistors is rated at 85
watts). By design, the power output of the transceiver is ALC-limited
to 25 Watts, in an effort to make it impervious to SWR problems
encountered in rugged field conditions, and to limit the current for
longer battery life. However, for amateur radio use, if the operator is
very careful to observe SWR conditions, it is possible to turn up the
output power somewhat, especially for SSB voice use. Exactly how much
power, is a balance between the desire for increased transmit signal,
and the possible damage which may occur to the amplifier's broadband
transformer, manual antenna tuner, output filters, and other output
components, etc. In amateur radio practice, it has been found
experimentally that it is possible to limit the SSB voice output to
about 40 Watts, without damage (if the operator is careful). There are a
few caveats however: (1) the CW injection, which determines the CW
output power, should be set to 6 Watts, (2) AM carrier level should be
set to 5 Watts, and (3) any digital
external modem level must be carefully limited to below 6 Watts
continuous power by careful adjustment of the audio drive (the
BAT.READ/LOW PWR. switch should be in the LOW PWR position for modem
Warning: Do this mod at your own risk!
modification should not be done if there is ANY chance that the the
radio may be deployed by operator(s) who are not familiar with the
nature of these cautions.
Image: Power output ALC setting: C24
|Kachina MP25 Power Output Mod Procedure
This mod assumes that all other alignments of the transceiver are at
recommended levels according to specifications detailed in the
Maintenance Manual, prior to beginning the modification procedure. The
mod increases the SSB power output to approximately 40 Watts Peak, while
keeping the CW level at 6 Watts and AM level at 5 Watts.
1. Disconnect the battery pack. Remove the outer enclosure, top cover, and whip antenna.
2. Connect an RF peak power meter and 50 ohm dummy load to the BNC antenna connector
3. Connect base station power supply or external supply voltage set to +13.8VDC
4. Set the ④ antenna tune lower knob all the way to the left 0 position
5. Set the ⑤ antenna tune top rotary switch to the 23 bottom vertical line position, which bypasses the antenna tuner
6. Attach a suitable microphone and a CW key
7. Turn on the transceiver and set frequency to 7296.0 kHz USB. Set the BAT.READ/LOW PWR switch to center position
8. Locate C24 the ALC adjustment, and make ready a suitable insulated tool for adjustment of it
9. Press the PTT and whistle into the microphone, observing the power output
10. Adjust C24 for the desired power output (Do not to exceed 40 Watts Peak)
11. Locate R240 the CW Level adjustment, and make ready a suitable insulated tool for adjustment of it
12. Switch the transceiver mode switch to CW, and hold CW key down continuously while observing the power output
13. Adjust R240 for the desired power output (Do not to exceed 6 Watts average)
14. Locate R259 the AM Level adjustment, and make ready a suitable insulated tool for adjustment of it
15. Switch transceiver mode switch to AM, press and hold PTT while silently observing the carrier level power output
16. Adjust R240 for the desired carrier level power output (Do not to exceed 5 Watts carrier level average)
17. Re-assemble the transceiver modules, covers, and enclosures.
18. Modification is complete.
Image: Kachina MP-25 power output mod, PC201 module, adjustment of CW Level and AM carrier level.
Photo: Kachina MP-25 final amplifier board (photo courtesy of teotwaki)
Replacing or Rebuilding the Kachina MP-25 Battery Pack
The Kachina MP-25 battery pack is out of production, so there is a need
to find a replacement alternative. The recommended solution is to find a
source for the new cells for the internal battery pack and rebuild it. A
Gel Cell or Sealed Lead Acid (SLA) type battery can be easily replaced
as an internal unit. But, for the NiCd battery, it takes 10 cells of
size D, with solder tabs, combined into a pack of a specific form factor
necessary to fit in the enclosure. The new NiCd cells can
be purchased separately and then soldered, taped, and/or bound by
shrink-tubing into the battery enclosure. The form factor is 7 cells in a
row, with 3 cells end to end along the top. There are 2 different MP-25
versions of battery pack holders. The First Version is an internal
battery with an aluminum frame and vacuum-formed plastic clam-shell
enclosure. The following photos and information are provided as an
example of rebuilding the MP-25 first version Kachina MP-25-BP (NC)
battery also known as SR-MP-25-BP (NC), with a commercially available
battery pack core of the proper form factor and configuration.
Disassembly of the battery pack aluminum frame. Remove the connector screws.
Slide battery enclosure out of aluminum frame.
Battery pack aluminum frame, clam-shell plastic enclosure, connector,
new battery pack, old battery pack. 10 NiCad D cells soldered in series.
Connector soldered on to the wires of the new battery pack. Battery pack
(TRW) connector pinout: Pin 1 is negative (ground) wide pin. Pin 2 is
12V+ positive (hot) thin pin. Re-assemble the clam-shell with Gorilla
Tape, but do not completely seal the seam between the clam-shell halves.
Keep a gap at the 4 corners of the clam-shell to release hydrogen and
oxygen gas that is emitted while charging. Re-assemble the enclosure
into the aluminum frame and re-attach the connector screws to clamp the
battery pack into the frame.
The battery pack core utilized in this SR-MP-25-BP (NC) NiCad rebuild was sourced from batteryspace.com (AA Portable Power Corp) Product ID 6535 Product Number PR-CU-R252
, a custom 12.0V 5000mAh battery pack made of 10 x D size NiCd cells
with 10" long 18 AWG wire with special configuration. The cells provide
about 25% more ampere-hour capacity than the original Kachina NiCd
battery pack did. This also means that the pack may need to be charged
about 25% longer than the original. A fully charged battery should read
approximately 13.5 to 14.0 V on the manpack front panel meter when
switched to the battery test position and while charging. Do not
Charging Battery Reminder: always loosen the 6
clamps of the manpack case cover while charging, and slightly let the
cover separate from the front panel gasket, to release the hydrogen and
Troubleshooting the Kachina MP-25
Common problem issues that may be encountered, and some possible solutions.
|Whip antenna mount breaks at thin brass fitting screw near rotary knob plate.
|| Rebuild with larger fitting (or braze and re-drill it)
|Lower Sideband reception and transmit is very weak, tinny or muffled sounding
|Replace FL102 BLE (16 MHz IF LSB filter)
...or use Upper Sideband on the HFpack calling frequencies! :)
|Continuous beep sound of unlocked frequency, combined with false digits on some ranges
||Repair or clean frequency selection rotary knob
switches. Sometimes just rotating each knob from 0 to 9 several times
will wipe them clean.
|CW chirp or keying interruptions due to semi-break-in keying
||Press microphone button and hold it down during CW transmissions.
|Transceiver front panel explodes out in a cloud of fire and ice
||Always loosen the outer enclosure panel clamps when charging, to prevent
gas pressure buildup inside the sealed enclosure case. Only set the
power supply charger to CHARGE if the battery is inside the radio.
Remove the battery pack when used as a base station then set power
supply to OPERATE.
|Frequency is out of calibration
||Calibrate the 2 internal crystals using the alignment procedure in
service manual section 5-36 [PC201 Alignment. 16MHz BFO crystal trimmer
C202] and section 5-31 [PC601 Alignment. 5MHz crystal PLL reference
oscillator trimmer C641]
|Display illuminates for too short of time for comfortable tuning
||Do the Display Timer Mod.
|Continuous tone emitted by radio speaker after some time or whenever transmitting
|The tone alarm will sound if battery voltage
drops too low. Check battery voltage. Charge battery. A tone will also
be heard if the CW key is shorted (key down sidetone)
|Battery completely dead, won't take a charge for long
|Rebuild or replace the rechargeable batteries in the battery pack.
| Intermittent problems appear out of the blue after radio has been sitting unused for some time
||Open radio up, loosen and wiggle all the module boards so they are
seated properly in their connector sockets. Sometimes these will corrode
after years of disuse, and the module boards will need to simply be
extracted and re-inserted.
Kachina MP-25 in the News
MP-25 manpack radio seemed to find its way into many remote places of
the world, including armed conflicts in Africa and Central Asia. Here
are some links to a few old newspaper articles, with some details on
rather "infamous users" of the Kachina MP-25 :)
Kachina MP-25 in Afghanistan (2001 article)
Kachina MP-25 in Kashmir (1998 article)