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Friday, December 27, 2013
SolderSmoke Podcast #157: Peter Parker on Phasing Rigs
SolderSmoke Podcast #157 is available for download.
http://soldersmoke.com/soldersmoke157.mp3
December 27, 2013
-- Santa Report: Rigol Scope at SolderSmoke HQ. Kites at VK3YE.
-- Project updates: Bill's BITX 40/20 build.
-- Peter finishing up BITX40 (in a big box)
-- BITX 17 (5 watts SSB) works JA, ZD7, ZS!
-- The mystery, elegance, and gentleness of phasing SSB
-- Phasing explained in 1970 ARRL SSB book
-- Phasing SSB: From Hallicrafters HT-37 to SDR
-- The SP5AHT Phasing Rig
-- I & Q for you: The Binaural Experience
-- Direct Conversion receivers and Software Defined Radios
-- Simple DC receivers plugging into sound cards
-- The joy of receiver building
-- 144 MHz aircraft bounce (Melbourne to Sydney)
-- VHF Across The Great Australian Bight
HAPPY NEW YEAR TO ALL!
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Wednesday, December 25, 2013
Santa Arrives at SolderSmoke HQ! Rigol and Black&Decker
Santa Claus obviously heard my distress call when the TEK 465 gave up the ghost. This morning it was replaced by a RIGOL digital scope. I'm going through the tutorials. Wow, lots of features. A Black&Decker jig saw also arrived -- this will help in my cabinetry efforts.
Last night just before dinner I talked to Kiyo, JH1MDJ, in Tokyo on 17 meter SSB with the 5 watt BITX. I kind of broke through a small pile-up and we then had one of those "please repeat your power level... I can't believe that is 5 watts to a dipole" conversations.
Happy Holidays to all!
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Labels:
Japan,
oscilloscope,
test gear,
workbench
Saturday, December 21, 2013
How they took the iconic Apollo 8 Earthrise Photo (Amazing Video)
I was ten years old and totally obsessed with the space program. This video brought back a lot of the magic. Wow. You really have to see this one.
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Labels:
photography,
space program,
video
Where to send all those LM386 chips: Make them BEAM robot brains!
Over in the BITX20 yahoo group there have been some comments about the shortcomings of the widely used LM386 audio amplifier chip. Many people don't like it because it is noisy. I don't like it because it is a chip. (In my BITX rigs I have replaced it with a simple discrete component audio amplifier.) So this morning I was pleased to find this video on the Maker blog that presents a very good use for all those LM386 devices: We can turn them into robot brains!
Make's video and web page on this project are both very good. One paragraph in the page kind of captures the reasons I dislike the LM386:
How It Works
The core of the “Herbie” circuit is the LM386 power amplifier chip. To simplify a bit, we can think of the chip as a “black box” with inputs and outputs that respond in predictable ways, and don’t have to completely understand what’s going on inside.http://makezine.com/projects/sunbeam-seeker-bot/
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Friday, December 20, 2013
Christmas Eve Fessenden Memorial Broadcast on 486 KHz
Imagine it is Christmas Eve, 1906 and you are on the air, listening to the harsh buzz of Ol' Spark Morse Code. Suddenly, in the headphones you hear a human voice and music.
Brian Justin has set up an experimental station that recaptures that magical "birth of radio telephony" moment. He will be on the air this Christmas Eve, Christmas Day and New Year's day. Here is what W4DEX heard during last year's event:
http://www.w4dex.com/500khz/wf9xih/wf9xih_24dec11.mp3
Experimenter to Honor Early Wireless Pioneers with Longwave Transmissions
As he has over the past several years, Brian Justin, WA1ZMS/4 -- as experimental station WG2XFQ -- will transmit voice and music on 486 kHz on Christmas Eve and Christmas Day and again on New Year's Eve and New Year's Day. Transmissions will begin at 0001 UTC and end at 2359 UTC. Justin, who may be better known for his microwave exploits on ham radio, will use an AM audio loop modulating his vintage-style, homebrew transmitter to honor Reginald Fessenden's Christmas Eve 1906 AM voice transmission.
"While his original transmissions used a set of carbon microphones in the antenna lead to modulate the signal," Justin explained, "WG2XFQ will be utilizing true Heising modulation in honor of Raymond Heising, who developed this early form of amplitude modulation during World War I.Justin constructed his 5 W master oscillator power amplifier (MOPA) transmitter using 1920s-vintage components. He said a modern 500 W FET linear amplifier allows him to meet his WG2XFQ ERP limit of 20 W. An RF engineer, Justin collects pre-1920 wireless gear and has a World War I Heising-modulated aircraft transmitter he's planning to restore. Justin was an active participant in the ARRL's WD2XSH 600 meter experimental project.
(From the ARRL Newsletter)
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Brian Justin has set up an experimental station that recaptures that magical "birth of radio telephony" moment. He will be on the air this Christmas Eve, Christmas Day and New Year's day. Here is what W4DEX heard during last year's event:
http://www.w4dex.com/500khz/wf9xih/wf9xih_24dec11.mp3
Experimenter to Honor Early Wireless Pioneers with Longwave Transmissions
Fessenden |
WA1ZMS constructed his MOPA transmitter from 1920s-vintage components. [Brian Justin, WA1ZMS, photo] |
(From the ARRL Newsletter)
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Labels:
Old radio,
radio history
Wednesday, December 18, 2013
BITX 2040 Build Update #2: Of Spreadsheets and VFOs
I continue to tweak the capacitors in my new BITX 20/40 VFO (scroll down to see it). On Sunday I added a little relay that will switch in some additional capacitance to move the VFO about 500 kHz. Without the additional cap, the VFO will be on frequencies suitable for 40 meters -- with the additional cap it will be on frequencies needed for tuning 20 meters.
I calculated that I'd need an additional 220 pf to make this shift ( I later went with 100 pf). In went the needed cap and relay. It worked. But there was a problem: On 40 I had the desired 175 kHz frequency range. But I found that with this arrangement on 20 I could only cover 95 kHz. Obviously my variable air cap with 44 pf in series was being "diluted" by the additional 220 pf being switched in by the relay -- with the additional capacitance, the change in total capacitance produced by the variable cap (with series cap) was smaller in the 20 meter range than it was in the 40 meter range.
Clearly, one solution was to play with the value of the cap that I had in series with the variable cap -- increasing it would increase the freq spread (both on 40 and 20). But how much should I increase it?
By this point I was getting tired of all the manual calculations. Time for a spreadsheet! I created one, and threw in the values of all the caps and of the coil, and the resonant frequency formula. I set it up to display and the resulting freq coverage.
The freq ranges in the actual ham bands is a bit off -- there may be some stray capacitance and inductance in the circuit that is not being captured in my numbers. But the important thing was the spread. The spreadsheet allowed me to see that with a 100 pf cap switched in by the relay and a 74 pf cap in series with the variable, I could cover 180 kHz on 40 and 123 kHz on 20. That's OK. This little exercise shows the usefulness of spreadsheets in dealing with this kind of calculation.
You can see my spreadsheet here:
https://docs.google.com/spreadsheet/ccc?key=0Ak4BJL1-oWiJdElieDY5Y2xVWUtSNDl0anRYLVBBeGc&usp=drive_web#gid=0
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I calculated that I'd need an additional 220 pf to make this shift ( I later went with 100 pf). In went the needed cap and relay. It worked. But there was a problem: On 40 I had the desired 175 kHz frequency range. But I found that with this arrangement on 20 I could only cover 95 kHz. Obviously my variable air cap with 44 pf in series was being "diluted" by the additional 220 pf being switched in by the relay -- with the additional capacitance, the change in total capacitance produced by the variable cap (with series cap) was smaller in the 20 meter range than it was in the 40 meter range.
Clearly, one solution was to play with the value of the cap that I had in series with the variable cap -- increasing it would increase the freq spread (both on 40 and 20). But how much should I increase it?
By this point I was getting tired of all the manual calculations. Time for a spreadsheet! I created one, and threw in the values of all the caps and of the coil, and the resonant frequency formula. I set it up to display and the resulting freq coverage.
The freq ranges in the actual ham bands is a bit off -- there may be some stray capacitance and inductance in the circuit that is not being captured in my numbers. But the important thing was the spread. The spreadsheet allowed me to see that with a 100 pf cap switched in by the relay and a 74 pf cap in series with the variable, I could cover 180 kHz on 40 and 123 kHz on 20. That's OK. This little exercise shows the usefulness of spreadsheets in dealing with this kind of calculation.
You can see my spreadsheet here:
https://docs.google.com/spreadsheet/ccc?key=0Ak4BJL1-oWiJdElieDY5Y2xVWUtSNDl0anRYLVBBeGc&usp=drive_web#gid=0
Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20
Sunday, December 15, 2013
20/40 BITX Build Update #1: VFO Success
I've started construction on my second BITX transceiver, this one for 20 and 40 meters. As with the previous rig, I decided to take the VFO first, but this time I pledged not to surrender, not to wimp out with a VXO or (worse!) a DDS. No, this time it would be a real LC VFO.
I took seriously all the admonitions in the tech literature about the fickle permeability of ferrite and iron powder, so this time I used an old-fashioned air-core coil. It is wound around a cardboard tube. The tube was previously the bottom portion of a coat-hanger from the dry cleaner. I wound 40 or so turns on this core, then measured the inductance: 5.6 uH -- that looked about right.
For the oscillator stage I used a Colpitts circuit very similar to the one in the original BITX schematic (but I am hoping I won't need the varactor diode fine tune mechanism). I had on hand a nice Heathkit 19-146 pf variable cap with an internal 4:1 reduction drive. Not wanting to pluck rotor places out of this beautiful part, I had to calculate the series capacitance that would yield a frequency spread of about 175 kHz. It turned out to be 40 pf. Then I had to figure out how much capacitance to put in parallel with the variable. Well, it all ended up like this:
There was a bit of trial and error in the process of getting the VFO to cover the desired range. A big help in all this was an on-line reactance calculator. I found this one to be very useful:
http://www.1728.org/resfreq.htm
I found that the VFO is more stable if I reduce the voltage from 12 volts down to about 8. Also, I found that when evaluating the stability, it is better (psychologically!) just to use a stable superhet receiver instead of the frequency counter. The counter may appear to be jumping around a lot, especially if the signal you are monitoring is not very strong. Just listening to it at zero beat on the superhet is very reassuring.
I followed the Colpitts oscillator with the FET buffer and two stage BJT amplifiers from page 50 of Doug DeMaw's QRP Notebook (page 50). I now have the requisite 7 dbm signal. And it appears to be quite stable.
I plan using this with an 11 MHz IF, with the VFO running at around 3.875--3.700 for 40 meters and 3.175 -- 3.355 for 20. I plan to use a small relay to switch in some additional capacitance to move the VFO down to the range for 20 meters.
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Saturday, December 14, 2013
University of Twente's Online Receiver
Wow, I played with this on-line SDR receiver a few years ago and thought it was fantastic. It is now even better. I'm sitting here listening to 40 meters in the Netherlands. Great stuff. Check it out. It is really amazing:
http://websdr.ewi.utwente.nl:8901/
Thanks to Bob, KD4EBM for letting me know about the updates.
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Labels:
Netherlands.,
SDR,
web sites
Friday, December 13, 2013
Circular Polarity and The Water Wheel in Dale's Moonbounce Amplifier
Bill:
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I'll attach some
pix of the feedhorn and LNA for you.
The importance
of circular feeds is that as a linear wave passes through the ionosphere, it
undergoes Faraday rotation. So it may arrive at the station you are talking to
having been twisted 90 degrees. This is a slow progressing process and on all
bands except 23cM, may cause EU for example to be locked out for hours at a time
for linear stations.
With circular
polarity, Faraday is a non issue. The feedhorn almost all of us use is a VE4MA
that has separate TX and RX probes. The circular polarity is synthesized as the
linear wave propagates down the circular waveguide and encounters sets of
capacity stubs. The exact opposite occurs for waves entering the waveguide. The
result is we get CW and CCW without having to use any relays (loss) and phasing
lines (loss).
My LNA has a
noise figure of under 0.24dB and uniquely connects to a protection relay with no
cable or adapters (loss).
The position of
the feedhorn and its scalar ring is tediously adjusted by measuring
the difference between sun noise and cold sky. W4SC developed a very accurate
and repeatable process that uses an SDR RX for this.
I use a
modified C band satellite drive system known as a polar mount so I only need one motor drive to track the moon.
Anyway, hearing
my own echoes off the moon was and still is the highlight of my amateur
career.
The photos are
the feedhorn + LNA, My first water cooled 500W tube amp, my previous 400W solid
state amp (mounts right at the dish). My current design is 600W solid state and
will also mount at the dish.
BTW, that little
circle in the middle of the tube amp is a paddle wheel that turns as long as
water is flowing. A tachometer on the wheel sounds an alarm and shuts down plate
voltages should the wheel stop turning.
I'll keep you
up to date on my BB RX progress- thank you again Bill.
Dale W4OP
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Labels:
amplifier theory,
EME,
moonbounce
Wednesday, December 11, 2013
The NASA Juno Fly-by "Hams say HI to Juno" Video (very nice)
Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20
Labels:
Jupiter,
satellites,
space program,
video
Tuesday, December 10, 2013
The QRP Mojo Ceremony
More from Lobstercon (from N2HTT):
http://n2htt.net/2013/11/24/there-are-lobsters-in-the-woods/
And thanks to Pete, VE2XPL, for alerting me to all this.
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Labels:
DeMaw--Doug,
video
Sunday, December 8, 2013
Need help with part construction...
Please take a look and see if you can help me figure out how to make this thing. The diagram is eschpecially illuminating.
THE
DIE-CAST DROP-FORGED PLASTIC
TRICHOTOMETRIC
INDICATOR-SUPPORT
Inquiries concerning the mounting of
the Trichotometric Indicator
Support indicate that some difficulty
is being experienced with the
brackets which attach the support. As
an aid toward fabricating the
support brackets, the accompanying
illustration is provided to show
the type of material as well as the
dimensional data needed. It will
be noted that in attaching the bracket
to the support a special ambi-
melical hexnut is used. The
application of this nut is unique in that
any attempt to remove it in the
conventional manner only tightens it.
Because of this design, the nut must
be fully screwed on before it can
be screwed off.
DRAWN BY
|
FRED SPOON
|
SCALE ¼”=1 MILE
|
NO. 43906
|
FILE – BAR NONE
|
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On the Wavelength of Santa's Sled (with a nod to FA Wilson)
About a year ago, David, M0VTG, was reading "From Atoms to Amperes" by FA Wilson. His thoughts turned to a seasonal application of Wilson's lessons.... Thanks David!
WAVELENGTH OF SANTA AND HIS SLEIGH
We're going to need to know the
following:
Total mass of the sleigh, reindeer,
Santa and his presents, and the speed at which the sleigh travels.
Assuming that the sleigh travels relatively close to the surface of
the earth, the mass can be regarded as the same as the weight. Now
assume each reindeer weighs 100 kg. Traditionally there are nine of
them so total mass of the reindeer is 900kg. Say the sleigh also
weighs 500kg and Santa and his presents weigh 400kg; then the total
mass is 1800kg. To get round all the children who believe in him in
one night would mean him travelling at a speed of say 1000kph (277.8
m/s). (Note that scientific notation for numbers used is that used
on some calculators)
So mass (m) is 1800kg
velocity (v) is 1000kph (notice
the not so subtle change from a scalar quantity to a vector
quantity).
Max Plank came up with a formula: E
= hf relates Energy to frequency
using h (Plank's
constant = 6.626 E-34 Joule seconds).
Albert
Einstien (as everyone knows) says that E = mc2
(where c is the velocity of light).
So it
follows that hf = mc2
and
therefore, m = hf/c2.
The
momentum of a photon (p) is
defined as mass x velocity or p = mv and
as every radio amateur knows, wavelength (λ)
is the velocity of light divided by frequency or λ = c/f
(or f/c = 1/ λ).
So mv
= hf/c2 x
c (velocity of a photon is c
don't forget); so p =
hf/c
Since
f/c =1/ λ, then p =
h/λ i.e. λ =h/p
Also
since p = mv then λ
= h/mv (This expression is known
as the de Broglie wavelength - Louis Victor de Broglie)
Notice that the
velocity of light does not directly feature is the expression. We
can, therefore use it the calculate the wavelength of anything!
So the wavelength
of Santa's sleigh is Plank's constant divided by the mass times the
velocity or
λ = 6.626
E-34 J s / (1800 kg x 277.8 m/s) which equals 1.325 E-39 m - an
unbelievably small number! Make up you own mass and velocity for the
sleigh if like.
I
defy NORAD to track such a short wavelength.
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Saturday, December 7, 2013
"Snort Rosin" Seal of Approval for "Ferrari-esque" Italian Wire Cutters
Hi Bill,
It's always nice to find something high-quality and inexpensive and today it happened to me so I thought I'd share my good fortune.
Having been in the professional radio repair business for 40 years (retired 2012), I very much appreciate quality hand tools. On my bench at home I have an expensive pair of Lindstrom wire cutters but in the field I generally resorted to cheaper, not so high-quality tools (in case of inadvertent loss). The problem at home is it seems like every time I need to grab my Lindstroms, they're not where I'm at so I've been on the lookout for a spare pair or two of quality cutters. Well, today in the Fry's Electronic newspaper flyer I saw an ad. for Hakko brand wire cutters on sale for $2.99, regularly $4.99, a 40% saving. Me being, shall we say, "thrifty", this immediately got my attention. I know Hakko markets some very good soldering related equipment, however until today I had no experience with their line of hand tools.
So, between some appointments this morning I stopped at our local Fry's store and checked out the cutters. I was expecting to find something typically cheap and made in China so imagine my surprise at discovering they are made in Italy! The part # of this particular tool is CHP-170 and is mfg. by the CHP Tools division of Hakko. The hand grips are palm-fitting and very comfortable with thumb and forefinger rests at the top of each for tool manipulation. The design is what I would call "Ferrari-esque"; bright red with black accents. Very pleasing to the eye. Turns out that The metal parts are high grade tool steel and Parkerized for low reflectivity and high wear and corrosion resistance. What impressed me the most is the cutting surfaces; they mate perfectly. So many inexpensive cutters have lousy mating surfaces, these don't. With the cutting edges 'closed', shining a high-intensity light on one side results in -no- light 'leaking' by the mated edges. That's first-class machining!
IMO, even at the typical price of $5 or so, these cutters are a bargain, especially considering the quality (how does one say, "it is very good!" in Italian?). So, if you or anyone you know is in the market for some great wire cutters, tell them that the Hakko CHP-170 has the "Snort Rosin" seal of approval, HA!
73.......Steve Smith WB6TNL
http://www.amazon.com/Hakko-CHP-170-Maximum-Cutting-Capacity/dp/B00FZPDG1K
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Labels:
Smith--Steve,
workbench
Friday, December 6, 2013
"The Amateur Scientist" by C.L. Stong (FREE!)
This great book is available on-line: You guys will really like it:
https://archive.org/details/TheAmateurScientist
Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20
https://archive.org/details/TheAmateurScientist
Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20
Labels:
books
Renaissance Man Illustrator for Scientific American
C.L. Stong wrote the "Amateur Scientist" column for Scientific American for many years. When I was a boy, my mom saved up to buy me the anthology of Strong's columns. It had a big impression on me -- I still have a copy on my shelf. I never gave much thought to the illustrations, but I now realize that they were responsible for much of the impact that that book had on me. The cloud chamber drawing was one of my favorites. Note the use of peanut-butter jars. Yea!
This morning an article on the Maker blog focused on the genius who did all those wonderful drawings: Roger Hayward (I wonder if there is any relation to Wes and Roger -- all three are from Oregon and all three are technical geniuses.)
I found this very nice web site about Roger Hayward: http://scarc.library.oregonstate.edu/omeka/exhibits/show/hayward/introduction/introduction/
There are great illustrations in many places. For the Scientific American drawings go to the 1960s section.
And check out this one:
From: http://scarc.library.oregonstate.edu/omeka/items/show/4456
Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20
Labels:
books,
Knack Stories
Thursday, December 5, 2013
W4OP -- Earth-Moon-Earth and Another Barebones Superhet
Years ago I bought a Barebones Superhet from Dale Parfitt on E-bay. Several years after that, having forgotten who I bought it from, I was asking questions about how to get it working on 17 meters. Dale jumped in with some very helpful e-mails. It took us both a while to realize that I was working on the receiver that he had built. Dale is active in a really wide range of ham radio activities, everything from QRP to EME. Check out his homebrew projects here (I really like his Solid State Drake 2-B!) http://www.parelectronics.com/par-homebrew-projects.php
And his vintage projects here: http://www.parelectronics.com/vintage-radio-restoration.php
And here's what Dale has been doing with the Moon (that's his 15 foot dish in the picture):
And his vintage projects here: http://www.parelectronics.com/vintage-radio-restoration.php
And here's what Dale has been doing with the Moon (that's his 15 foot dish in the picture):
Hi Bill,
I thought of you today when I won a Bare Bones Barbados RX on
eBay for $5. I am going to team it with a DDS VFO and a matching
TX.Some parts are apparently missing, but i have a huge junk box
and also know how to order from Mouser should the junk box fail me.
Right now I am putting my solid state 650W 1296MHz EME amp ,
Power Supply, meters etc. in its waterproof cabinet so I can mount it right at the dish
and not incur any feedline losses.
1296 is probably the best EME band. Power is getting easier and
easier to acquire (although solid state is around $5/watt), dishes are fairly
easy to acquire or build and perhaps most importantly, we all use circular
polarity feeds with no relays/hybrids. Activity weekend can sound like 20M, with
a number of stations just ragchewing on CW and SSB.
73,
Dale W4OPfor PAR Electronics, Inc.
http://www.parelectronics.com
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Labels:
DeMaw--Doug,
Drake 2B,
EME,
moonbounce
Wednesday, December 4, 2013
Thermitron (Tube, Valve) Op-Amps
It is kind of appealing. I like it better than the 741. This one you can take apart and see how it works. Thanks Rogier!
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Labels:
radio history,
Tubes
Monday, December 2, 2013
On the suffering of Geeks. Indeed, we suffer...
Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20
Labels:
Knack Stories
Sunday, December 1, 2013
11 MHz IF for new BITX 20/40 Dual Bander? Also: Cabinetry and Socketry
I am gathering parts and
ideas for a BITX dual bander (20 and 40 meters). I know Farhan used a 10 MHz
filter for his "Simple SSB Transceiver." But I was thinking of going a bit
higher, to 11 MHz. This would allow me to run the VFO from 3.175 to 3.355 for 20
meters, and 3.695 to 3.875 for 40 meters. I'm hoping that I can do this with one
single VFO (Farhan used two VFOs), perhaps with a reed relay switching in some
additional capacitance for the other band. I'll also follow Farhan's lead and
switch the Low-Pass and Band-Pass filters with DPDT relays.
I set up a simple
spread sheet and looked at the VFO harmonics to see if any fell within the
desired tuning ranges. That looks OK. I have not looked at mixing products
between VFO and BFO. What do you folks
think? Would the 11 MHz IF for these bands work? Or are there evil birdies
lurking in my future?
I've gone ahead and
bought another wood box for the new rig (I didn't even have to suffer through a
second visit to the crafts store -- they are available on Amazon). I also got a
roll of copper sheeting at Home Depot. This time I will prepare the box
first, lining the inside with copper and preparing all the "socketry" (George
Dobbs' word) before putting the PC board in.
Labels:
BITX20,
Dobbs-George,
Farhan,
SSB
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