Thursday, September 14, 2017

Mizuho MS-1 microphone wiring for MX-serie radios

Hi all,

as some of friends asked me which kind of microphone will work with MX series of Mizuho transceivers and which kind of microphones used Mizuhos originally there I am sharing what I know about it.

For external Mic. need to be inserted the 3.5mm diameter jack plug. See the picture which is available in original manual including the points (6) and (7) regarding the external microphone and external speaker usage.

The microphone connection wiring is diferent from the MX-3.5S and MS-1 external speaker/microphone should be used.

There is the schematic diagram of the MS-1 speaker/ext. microphone made by Mizuho.

The MS-1 won't work with the older radios like MX-2, MX-6, MX-10Z, and MX-15 handheld SSB/CW transceivers because the microphone plug wiring is different than on the later Pico MX-series handhelds.
The another external speaker/microphone M-4 model by Mizuho should be used.

The 40mm diameter, 8Ohms, 0,35W speaker is used in MS-1 and the 600Ohms Mic line. The microphone plug and external speaker plug are integrated into molded common connector which is the difference from the M-4 btw. The PTT switch only connects and disconnects one wire.

Hope it helps,

73 - Petr, OK1RP

Thursday, September 8, 2016

The Mizuho PL-15 amplifier driven by MX-21S...?

Hi all,

an interesting question came last days from John, W8BCR regarding the PL-15...

"So I have an mx-21s radio. I have a line on a pl-15 model amp. Are these compatible? Or do I have to find a pl-21 model amp? Any info would be helpful! Thanks, John W8BCR"

The PL-15 is dedicated for MX-15 transceiver from Pico series. (together with VX-15 ext. VFO) This amplifier is designed for 300mW exciter as the MX-15 radio has this power output level.

The PL-21S is dedicated for MX-21S transceivers and it is driven by them at 2W power level.

Both amplifiers are using the same transistors but in different
conditions... Your PL-15 is using 3dB attenuator in the input and 1Ohms resistor to the final 2SC1945 base...

while PL-21S is using 6dB attenuator in the input and 3Ohms at the base of 2SC1945.

The rest of the amps is same...

So in order to avoid over-driving the PA by PL-21S radio or damage the transistor you should change the components inside or if you would not like to do anything inside of the PA (to keep it collectible)then I propose to try use the external RF attenuator in the input of the PL-15 to jump your exciting power from MX-21S handheld down to approx. 300mW.

The best way is to measure the real power output from your MX-21S into dummy load (I am expecting something around 1.5W out) and then make an appropriate attenuator to get 300mW output for your PL-15 amplifier.

The rest of the both amps is same including the cables so I am confident it should work for you.

Hope it help,

73 - Petr, OK1RP

Wednesday, July 20, 2016

DX Handy 10m does not transmit on SSB... hints for debugging


one of the issue which can happends on the Mizuho handies is lack of SSB TX as reported by John, W8BCR...

"Ok, so I confirmed my dx handy 10 meter receives, and I confirmed with another radio that it transmits CW. It does not seem to transmit voice. When I push in the PTT, I hear a quick static noise accompanied with a flash of the transmit light but it does not remain on while I hold the PTT in. At this point I can use the built in keyer and transmit CW, but no voice. Any ideas where to start? Thanks, John W8BCR

There are the hints and tips from our family members as follows:

Likewise i have a couple and both obtained cheap as faulty and not receiving. Both had the same problem which is that due to the weight of the xtal filter and its soldered connection on the pcb if the radio is dropped then the filter breaks away at the solder joint and hey presto NO REC.
quick solder job and back in business again .

Hi, I have a collection of nineteen (19) MX radio's , most problems I have encountered have been due to dirty slide switches, especially the SSB/CW change over, blast them with switch cleaner and rattle them up and down until your arm aches.
Peter G0KOK

More details about this troubleshooting you can find on Mizuho and Nishi Musen Reflector by Caitlyn, K9NI over here:

Hope it helps to more owners,

73 - Petr, OK1RP

Thursday, February 11, 2016

Where to buy Mizuho radios - short guide

As I am getting lot of emails regarding the purchasing Mizuhos there I am posting my few hints where to look for them.

Unfortunately it is very hard to find Mizuho for sale now. Most of the Mizuhos become collectibles and they are not available for sale at all. In rare cases they are going very high...

As the starting point with Mizuho radios I can recommend to looking for MX-21S which is the best choice for on-air operation/DXing I guess. Also there was huge production of MX-21S I guess so this model is not as rare as MX-14S or even worse MX-18S or MX-24S, MX-2F etc.

Sometime you can find Mizuho on eBay, but nothing currently available if I remember well.
If you would not like to get tons of MIZUHO KAZAMI figures in your search results :( then I can recommend to put as key word "Mizuho transceiver" or "Mizuho QRP" or combination with something related to ham radio in the searching tool...

Also you can join our group here:
and try to ask members if someone would like to sale something.

Also please try to check these swappments:,23.0.html

The most important when you are looking for Mizuho radios is:
but be prepared for japanese language and registration with prepaid is needed.

Hope it helps a bit.

best regards,
73 - Petr, OK1RP

Thursday, January 28, 2016

Converting Mizuho MX-21S to MX-24S

Unfortunately the copy is in horrible quality. If you will have problem to read some parts then do not hesitate to ask me for help.
Please take a note that there is error in frequency range in the top of the document. When it will be equiped with 24X89S and 24X94S xtals then the total frequency range should be 24.890-24.990MHz (50kHz per xtal) instead of "24.89-24.94mhz".
Also unfortunately I do not remember where I got it years ago and I did not found the source even now. So if somebody know it or even better the author of this article will read it over here then I will be happy to contact me in order to ask for permission to post it and put the copyright note here.
73 - Petr, OK1RP

Tuesday, January 26, 2016

MX-6S 12V power modification by Steve, WB9DAS

Steve Johnston,  WD8DAS

1.  Remove the four black screws and plastic washers holding the front panel to the radio frame.  Remove the front cover by gently pulling it away from the radio frame.  Watch out for the wires going to the speaker and microphone.

2.  Remove the OPTION switch by unscrewing the tiny black screws mounting it to the bottom panel.  Cut the white wire that goes up from the switch to/ the top of the board, and unsolder or cut the resistor going from the switch to the grounded transformer can nearby.  The removal of the OPTION switch makes room for the installation of the ten volt regulator.

3. Locate a 7810 three-terminal regulator and bend its heatsink to fit against the bottom panel while the regulator sits parallel to the front panel. This means that the heatsink will have a 90 degree bend.  Attach the heat- sink to the bottom panel -- either with a tiny machine screw and nut, or by loosening the other hardware on the bottom panel, and slipping the heatsink between the layers of sheet metal.  Then retighten the other hardware. I found that some versions of the 10 volt positive regulator come with a very thin heatsink that makes this sort of installation possible.  The usual 7810 regulator heatsink is too thick, and screw/nut mounting is the only way.

4.  Locate the orange wire running from the center pin of the external power jack (with diode installed) to the power switch.  Cut this wire where it passes the new regulator, and solder the end from the power jack to the INPUT terminal of the regulator.

5.  Install a diode (1N4003 or higher) on the OUTPUT terminal of the new regulator, anode toward the regulator (arrow pointing away from regulator, in other words).  Now attach the other end of the orange wire (going to the power switch) to the cathode of the new diode.

6.  Nothing need be attached to the GROUND pin of the regulator if the heatsink is grounded well.  If in doubt, add a wire from the GROUND pin of the regulator to the spot where the OPTION resitor was grounded to the transformer can.

How it works...  The old diode on the center pin of the power jack protects against accidental application of reverse polarity.  The incoming 12v goes to the regulator and is dropped to 10v.  The new diode drops the 10v down to 9.3 volts (ideal for the radio), AND blocks drainage of the internal batteries by the new regulator.

Steve Johnston, WD8DAS
September, 1990

All rights reserved to Steve / WD8DAS

Crystals for the Mizuho MX-series

There is pile of the informations about the crystals and calculations for the MX-series...
MX xtals specifications:
Funamental mode
60 pF internal capacitance
0.0010 % tolerance
AT-crystal cut
HC-25 case
The formula and examples for MX-21S:
16.2670MHz = 21X-25 xtal label ; it covers 21.25 - 21.30 MHz range.
Generally take the xtal frequency, multiply it by 2, then subtract the IF frequency.

Fx = 2x(Fo) - 11.2735  [MHz; MHz; MHz]
16.2670 X 2 - 11.2735 = 21.2605 (lowest frequency)
16.1647 X 2 - 11.2735 = 21.0559 (lowest frequency)

Some examples of the crystals for MX-6Z:
28X30 - 13.20990 (28.30 to 28.35)
28X35 - 13.22682 (28.35 to 28.40)
28X40 - 13.24373 (28.40 to 28.45)
28X45 - 13.26059 (28.45 to 28.50)
The formula for the MX-6Z is in the back of it's manual:
       (Fo + 0.05 - 7.7975)
Fx = ------------------------ - 0.005
Example: 50.10 = 14.11700 MHz
Fo = Crystal Frequncy
Fx = Lowest Operating Frequency
Example: 50.10 = 14.11700 MHz

The rest of the 10M crystals are:
28X00S 28.000 - 28.050 MHz 13.10853 MHz
28X05S 28.050 - 28.100 MHz 13.12544 MHz
28X10S 28.100 - 28.150 MHz 13.14233 MHz
28X15S 28.150 - 28.200 MHz 13.15923 MHz
28X20S 28.200 - 28.250 MHz 13.17612 MHz
28X25S 28.250 - 28.300 MHz UN
28X30S 28.300 - 28.350 MHz UN
28X35S 28.350 - 28.400 MHz 13.22682 MHz
28X40S 28.400 - 28.450 MHz 13.24373 MHz
28X45S 28.450 - 28.500 MHz 13.26059 MHz
28X50S 28.500 - 28.550 MHz 13.27750 MHz
28X55S 28.550 - 28.600 MHz 13.29457 MHz
28X60S 28.600 - 28.650 MHz 13.31161 MHz
28X65S 28.650 - 28.700 MHz 13.32866 MHz
28X70S 28.700 - 28.750 MHz 13.34571 MHz
28X75S 28.750 - 28.800 MHz 13.36275 MHz
28X80S 28.800 - 28.850 MHz 13.37980 MHz
28X85S 28.850 - 28.900 MHz 13.39687 MHz
28X90S 28.900 - 28.950 MHz 13.41391 MHz
28X95S 28.950 - 29.000 MHz 13.43094 MHz

The formula for the MX-6S:
         (Fh - 11.2735)
Fx = ------------------------
Fx = Crystal Frequncy
Fh = Highest Operating Frequency
Example: 50.100 to 50.150 = 12.95883 MHz

The MX-3.5S:

IF : 11.2735 MHz
XTAL : 14.83700 MHz
VFO : 25kHz
3.5XX00S 3.500 - 3.525 MHz 14.83700 MHz
3.5XX50S 3.550 - 3.575 MHz ...

The MX-6S:


50.000 - 50.050 MHz

12.92550 MHz



50.050 - 50.100 MHz

12.94216 MHz



50.100 - 50.150 MHz

12.95883 MHz



50.150 - 50.200 MHz

12.97550 MHz



50.200 - 50.250 MHz

12.99216 MHz



50.250 - 50.300 MHz

13.00883 MHz



50.300 - 50.350 MHz

13.02550 MHz



50.350 - 50.400 MHz

13.04216 MHz



50.400 - 50.450 MHz

13.05883 MHz



50.450 - 50.500 MHz

13.09216 MHz


Thanks to Dave, WB0GAZ we have very complete information about the MIZUHO HT range xtals from ICM (LONG)

From: David Feldman (
Date: Fri Jan 05 1996 - 16:35:50 EST
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73 Dave WB0GAZ

This file was posted JANUARY 5, 1996 from WB0GAZ at

Last year I worked with International Crystals to develop a set of "standard"
part numbers for the range crystals used in most of the MIZUHO hand-held QRP
SSB/CW HF rigs. Through a set of analyze/duplicate/test cycles I got some
reasonable results (I guess you'd call the results reasonable - at least they
weren't awful!) I spent some good $$ at this - looking back it was a rather
crazy project, but I really am a sucker for cute little radios so it was

Toward the end of 1995, ICM instituted a (rather high) minimum+hourly charge
to test/analyze crystals, so I gave my project up once they set that policy
in place. At this point I don't plan to try to refine the parameters any more,
so I think it's time to post the part numbers as they stand. I do hope to get
feedback from hardy soles that actually try to use this info, and based on
that perhaps we can make minor "tweaks" and other corrections that will
improve the parameter sets. I'd also like to be able to publish a set of
frequency-calculation formulas (see below) so if you have access to some of
the formulas for the various Mizuho radio models, I'd be most grateful to
accept a copy of the info and include it in a subsequent posting.

Please feel free to use this list, but at your own risk, because it turns out
Mizuho (in Japan) hand-selects range crystals they have manufactered to get
ones that track accurately the frequency dial on the radio. My results have
similarly been rather variable, and I don't have the luxury of having a whole
batch of crystals made and hand picking the right ones.

It is feasible to have crystals shipped directly from Japan but it's rather
expensive (postage, Faxing your order in and getting it confirmed, exchange
rates, Yen-denominated cashier's checks, etc.) and some of them (such as for
the 2M band, etc.) aren't made anymore at all, and others (such as for the
US phone 40M band) aren't made except by special order (really a complicated

I didn't investigate the MX-3.5S (I felt the radio was of really limited use
in the US as the US phone band is far above where the MX-3.5S is designed),
the MX-6S (or AEA DX Handy for 6M) as I didn't have a sample unit, or the
MX-18S as my unit arrived with two crystals to cover the entire 18.068-168
MHz band and I didn't want to spend the $$.

Please note that for 15, 10, 6 and (possibly) 2 meters there are actually two
different flavors of Mizuho radios. The "S" suffix units have 1-2 watts of
output power, were sold only assembled, and use a 11.2735 MHz IF. They are
the more common types. The MX-15, MX-10, MX-6Z, and MX-2 units (no "S"
suffix) are 1/4 to 1/2 watt, were sold either kit or assembled, and use
a 7.795 MHz IF. I have no idea why two different IFs were necessary (maybe
cost?) but the range crystals are COMPLETELY different. You can't use a
MX-10 range crystal in a MX-28S even tho both radios are intended for the
10M ham band. The AEA DX HANDY for 10M is also called MIZUHO MX-28S. There
is a 1 watt 2M rig (the Santec LT-202S) running around but I've never seen
one, so I couldn't try to get crystals made for it. If anyone wants to sell
me their Santec LT-202S..............

!This info DOES NOT include the formulas needed to calculate a crystal's
!frequency given the range you want to cover. For that, you're on your own.
!I discovered also (much to my chagrin) that some of the rigs don't seem to
!have a completely linear relationship between target range and crystal
!frequency, at least as well as I could determine, and some of my attempts
!backfired (off by 5-10 kHz from desired range). The ways I found to pick
!a crystal frequency were either (1) work backwards knowing the desired
!coverage and the radio IF and crystal multiplication factor, or (2)
!interpolating/extrapolating a known crystal onto a new frequency knowing
!the crystal multiplication factor. The one thing I can tell you is that you
!derive the crystal frequency by specifying the TOP END of the desired
!coverage range (i.e., if you want to cover 21.150-21.200, you use 21.200,
!the IF, and the multiplication factor for that particular radio to obtain
!the crystal frequency required). IMPORTANT: ICM DOES NOT HAVE THE NECESSARY
!INFO ANY MORE THAN I DO! In a later version of this file, if people can
!pull together the necessary formulas based on documentation they may have,
!then this situation will probably improve (that is, if you have written
!formula docs from MIZUHO on your radio(s), then please copy me and I'll
!include in this file for a later posting). Also, if you have some "REAL"
!Mizuho crystals in your equipment, if you let me know the standard Mizuho
!part number (i.e., 14X20S) and the frequency stamped on the crystal, I'll
!accumulate a table of frequencies and that should simplify the ordering
!process by eliminating the calculation step altogether.

The range crystals are all fundamental types, and usually have 60 pF load
capacitance (yes 60, not 32), and there is another parameter that ICM calls
"C1" which determines the amount of "pullability" of a given crystal - that
is how far it will cover in the VXO circuit. If you don't specify this
parameter when you have a crystal made (that is, if you specify only the
frequency, holder and load capacitance) then ICM will choose a "C1" value
by default which is usually much too low. I think this is what has lead to
frustration in some prior efforts at getting range crystals made - the result-
ing crystal would cover (say) only 30 kHz of the band rather than the desired
50 kHz. My first ICM crystals had this problem, along with some crystals I
have that were made by JAN CRYSTAL. I chose ICM for this project because I
got very good support from one of their engineers.

Anyway, after considerable thrashing/expense/time ICM and I concocted 8
"standard" part numbers that are reasonable attempts at getting sufficient
VXO coverage. Some of the formulas seem to overshoot (beyond the lower end
of a given range) but that's not entirely bad - the radio's don't have
digital readout or even very fine mechanical readout, so it's a bit of a
shot in the dark. I'd suggest before actually putting your MIZUHO on the
air with any given crystal that you pre-test it on a frequency counter and
make up a little table that maps the (5 kHz) knob divisions to the actual
frequencies you get with your particular radio and crystal.

The MIZUHO radios don't have an elaborate set of adjustments to help each
crystal properly track the knob markings. There are no independent trimcaps
for the crystals. You plop in your crystal and pretty much take what you're

If all of this sounds like too much trouble and you want a SSB/CW HT for
HF, then the only other choice I'm aware of is the Tokyo Hy Power HT-750
(see October 1994 QST page 60 or so).

Anyway, here are the part numbers I have and the results of the LATEST test
crystal I had made. As you can see some of the crystals didn't meet the mark,
but perhaps you can improve on it...

                                        (RESULTS OF LAST TEST ATTEMPT)
ICM # Description Attempt Actual Freq
725677 MIZUHO MX2 T/R 144 MHZ BAND PENDING (update next time)
725678 MIZUHO MX15 T/R 21 MHZ BAND 21.250-21.300 21.255-303 9.70513
725679 MIZUHO MX14S T/R 14 MHZ BAND 14.300-14.350 14.282-352 12.81307
725680 MIZUHO MX7S T/R 7 MHZ BAND 7.175-7.200 7.167-197 9.23975
725681* MIZUHO MX6Z T/R 50 MHZ BAND 50.090-50.140 50.082-141 (later)
725682 MIZUHO MX10Z T/R 28 MHZ BAND 28.350-28.400 28.333-391 12.06667
725683 (not part of this series)
725684 MIZUHO MX21S T/R 21 MHZ BAND 21.250-21.300 21.257-299 16.29025
725685 MIZUHO MX28S T/R 28 MHZ BAND 28.400-28.450 28.403-450 13.24283


There you have it. This posting implies no relationship I have with ICM other
than being a customer for this project. If you have another way of getting
range crystals, I'd be interested in hearing of your experiences so I can
add information to this file and post it again. Also, you CAN get most of
the common range crystals from Japan if you're making a trip over there.

P.S., you may wonder if I have some of these radios.
Yes, I do.
No, they're not for sale ;-)

Good luck!

73 Dave WB0GAZ
All rights reserved to Dave / WB0GAZ
Thank you very much to Dave, WB0GAZ for his effort and good job in order to sumarizing the information about the ICM supplier third-party xtals for Mizuhos.
Please be noted that in original text was the bug > marked in red. The correct IF frequency is 11.2735MHz instead of 11.2785MHz which seems to me like the typo error.

73 - Petr, OK1RP

Monday, January 25, 2016

The true about the MIZUHO name...

"MIZUHO" means beautiful riceplant. The owner JA1AMH Mr.Takada named his company as he wish everyone to remember the beautiful country and free quiet life with his QRP radio goods in this busy world.

( Thanks to Junichi Nakajima / JL1KRA )

Thanks to Caitlyn, K9NI and Rod, KH7L we can understand it better while reading...

On that official website Mr. Tsugo Takada, JA1AMH, explains the reason the name Mizuho was chosen. Here is a translation from the Japanese:
"In days gone by, Japan was known by the name of Mizuho, "the land where beautiful rice plants grow in abundance". The water was pure and clean - and the rice plants would ripen every autumn. It was a beautiful country with an abundance of nature.
In recent years, while human life has become ever more convenient, our calmness and the precious feeling of nature has been lost. Even with your busy life, I would love for you to enjoy Musen (Amateur Radio) and to feel relaxed. For this reason I chose Mizuho Communications as the name of the company."
NOTE: It is very difficult to precisely translate the term Mizuho into English. To many Japanese it is an expression that is poetic, romantic and sentimental. It generally evokes images and longings for an idyllic, peaceful past. This is but one possible translation.

(Caitlyn Martin / K9NI, Mizuho Reflector founder)

All rights reserved to Junichi / JL1KRA, Caitlyn / K9NI and Rod / KH7L

Available Mizuho MX series QRP gears later...

The MIZUHO MX series QRP products with my comments here are just as an information for foreign QRP friends. It was possible to purchase them 10-15% off at amateur radio retailers in Tokyo ($1=YEN125) in 2000-2007.

Transceiver(we call them Pico series):

MX-6S 32,000yen 50MHz SSB/CW 1W

MX-7S 32,000yen 7MHz SSB/CW 2W

MX-21S 32,000yen 21MHz SSB/CW 2W

PL-6S 21,600yen 50MHz Linear 10W

PL-7S 21,600yen 7MHz Linear 10W

PL-21S 21,600yen 21MHz Linear 10W

The smallest CW/SSB transceiver in the world. 
S/RF meter, Noise-branker, Attenuator installed handy talky type QRP rig. VXO A/B channel selection of each 50Khz(below 7MHz:25KHz) coverage. IF is 11MHz.11Tr 3IC. The company sporadically make 3.5,14,18,28MHz version. It is very difficult to buy them because many amateur want to have it. Now only completed Pico transceiver is supplied. I suppose many failed to complete kit and troubled company.

Options for Pico:

PM1 3,300yen DC-DC converter

MS-1 4,600yen SpeakerMic

PR3-S 4,500yen Lack mount (MX,CW-2S,PL)

CW-2S 8,400yen CW semi-break-in unit /w sidetone

BM-6 1,500yen lather bag

PS-2 3,600yen AC adapter

Crystal 1,800yen any desired 25/50Khz band

PAN-62 5,200yen pocket dipole 50/144

AN-50 3,600yen 50MHz lod antenna

AN-7 4,800yen 7MHz lod antenna

AN-21 4,800yen 21MHz lod antenna

Pico need 9V power (AAA battery x 6). Feeding 12V will destroy the unit. I think the DC-DC is expensive you can make 9V with 7808 and one Di between the GND. CW-2S is recommended for CW operation.

Kits and misc.:

QP-21 3,000yen 21MHz 1W CW transmitter

QP-7 3,000yen 7MHz 1W CW transmitter

CK-1D 9,000yen Currtis Electric keyer

VFO-5D 6,000yen stable 5-5.5M VFO module

VFO-5D 6,000yen stable 7-7.1M VFO module

MA-1 1,300yen audio amp module

MA-20A 2,000yen Mic amp module

PF-1A 2,500yen CW peak filter module

KX-50K 8,000yen 50MHz antenna coupler

QP series are the most famous kit with fixed crystal.
It does not change the price more than 10 years. The VFOs are sealed module with iron case.Japanese QRPer use this unit to avoid difficult unstable VFO problem which annoys other station.