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Saturday, January 28, 2017

SolderSmoke Podcast #193: BITX 40, OLEDs, KWM-4, Noise Abatement

SolderSmoke 193   28 Jan 2017

Report from Pete on BITX 40 Session with California radio club.

Update on the BITX40 Module Revolution
-- Check out the BITXHACKS page.  Send in contributions.
-- BITX20 mailing list very active.
-- Raduino!
-- Interview with Farhan with W5KUB --   Eliminating the commercial gear.
-- BITX 40s on the beach in Australia.  FB

Bench Reports:

-- Color Displays!
-- KWM-4

-- Fixing up the old HT-37   HT37 to HT37 QSO with W1ZB
-- Dabbling in VHF with Ramsey Aircraft band receiver.  NOT FUN.
-- Going all IC with Si5351 OLED NE602 rig.
-- OLED Noise and the Active Decoupling solution.

Using LTSPICE as a diagnostic or understanding tool.

Of Waterfalls, Homebrew Rigs and Casual Critics on 40 meters. Words of Wisdom from W8JI.


Some great recent interviews by Eric 4Z1UG:
Ian G3ROO  Origins of ROO   Regen at age 8
Hans Summers G0UPL     Balloons!   NO COMMECIAL GEAR
Rob Sherwood NC0B 


Chris KD4PBJ's BITX 40 with improved stability
Jerry W0PWE built a DIGITIA!  Very nice.  Worked Keith N6ORS and heard me! TRGHS
Mike AB1YK's Al Fresco Scratch built BITX.  But give that LC VFO another chance Mike!
Steve N8NM 30 meter rig with salvaged CB LC VFO. FB
Keith N6ORS Franken SDR rig with parts from the 1980s.  FB
SKN Bandscan from Mike WA6ARA  I worked W1PID Jim!
What is Mikele up to?
Rocking Johannesburg and Kirghizstan via local repeaters:

Friday, January 27, 2017

When Bypass Caps are Not Enough: Active Decoupling

I was having a noise problem with my NE602 Si5351 OLED display receiver.   There was an annoying high pitched whine in the audio output.  The source was easy to identify:  If I reached in and unplugged the OLED display, the noise disappeared.  

Next I had to find out how the OLED noise was getting into the rest of the receiver.  It could have been through the SCL SDA or even the ground lines.  It could have been just through capacitive or inductive coupling from the display board itself.  A big clue came when I tried powering the display from a completely separate power supply: BINGO! The noise disappeared. So I knew the noise was going into the rest of the receiver through the Vc line that powered the OLED. 

I had been powering the OLED from the 5V regulator on the Arduino Uno. In an effort to isolate the noise, I put a separate 5V regulator in the circuit for the OLED.  No joy -- noise still there.  I then tried putting an RC low pass filter between the OLED and the 5V regulator.  Still had the noise.  Finally I remembered something from the AF AMP circuits of Roy Lewallen, Rick Campbell and Roger Hayward. ( I think Roy was the pioneer on this one.)  They all used an "active decoupler" between the first AF amp and the power supply line.   I confirmed that it was my first AF amp that was picking up the OLED noise.   I built the active decoupler (just three parts!) and the noise disappeared.  GONE! 

There are only three parts, but the way this circuit works is kind of complicated and not very intuitive.   There is a good discussion of how it works here:


Roy, Rick and Roger were using this circuit to knock down 60 Hz AC hum, but I found that my OLED noise was at around 200 Hz -- I figured (correctly) that the active decoupler would take care of this as well.   I think this little circuit can be useful in dealing with the kind of noise generated by the digi displays that many of us are now using.    

David Rowe has a really interesting analysis of this circuit here:

Thursday, January 26, 2017


Hi Guys!

I have to admit something. It's a learning experience.
A year or two ago I bought the Bitx boards from Sunil in India and while they are on the To Do list, haven't been built up yet. I have close to 20 projects on my to do list, so when Farhan's prebuilt SMT version became available I decided to get one.
I had gone over to TenTec before they shut down and bought a few of their two piece enclosures since I like how attractive they are and also inexpensive.
The Bitx went into the enclosure quickly and I measured a little over 10 W out with my scope. I fed a -125 dBm signal in using my HP8640 generator and could easily hear the tone.
So a really sensitive receiver. Nice and quiet too!
I got a SMT digital dial from QRP Guys and got it in the case. Now I heard a high pitched whine in the background. Nuts!
So I posted to the Bitx yahoo group asking for help in reducing the noise. I built a R/L/C filter network, added ferrites, built a copper clad and brass enclosure for the display. Nada. Noise still there. Adding adhesive copper tape didn't help either.
This was driving me mad. For some reason, and I don't know why, one evening I decided to try a gel cell. Success!!! No noise whatsoever.
Here's what happened....
When I first built the radio in early December I tested it on my operating bench. On that bench is a older Power Designs 0-60V 0-5A linear bench supply.
After adding the display I did integration on my soldering lab bench and for that I grabbed my HP E3610 supply which it turns out is heavy but switching, not linear. The noise was coming from the supply!!
If I hadn't tried the gel cell it may have taken me a long time to figure this out.
Saturday of last week was my first contact with it. I worked two Canadian stations with it, and both came back to me the first time  after I answered their CQ's. I did have one issue and that's the well documented drift. During the QSO I watched the display drift upwards as I held the PTT button down. I replaced the 100 pF and 47 pF chip caps in the VFO with disc ceramic parts from Mouser and now it doesn't drift.
While doing the work in the VFO section I also tweaked the trimmer cap a bit to bring the bottom range up to the start of the phone band, as before the bottom end was below 7 MHz and I figured that didn't do me much good for a SSB rig to waste a lot of its tuning range on the CW segment.
Here are a few pictures. Mic is home brew too, having made it for my MMR-40 rig.

Hope all is going well for you and looking forward to the next Solder Smoke.

Chris KD4PBJ

Monday, January 23, 2017

Fifteen Back Iissues of "Hambrew Magazine" (from the 1990s) Available Online

They look very interesting.  I saw an article by Wayne Burdick.   Doug DeMaw was involved.  Thanks to Tim at Arrow Antennas for making these back issues available.

You can download the .pdf files here:  


Sunday, January 22, 2017

HB2HB: N6ORS, W0PWE (and me!)

This is so cool.  Jerry W0PWE has built a magnificent BITX.   With a digital VFO and Termination Insensitive Amplifiers, I think it qualifies as BITX DIGI-TIA #2.   Running it "al fresco" he was tuning around on 40 and he heard DIGI-TIA #1 (mine!).  As soon as he finished soldering in the power amplifier, he put it on the air and, in his second contact, worked Keith N6ORS -- Keith was running his MIN-X rig.  Clearly TRGHS. Great work Jerry!
Hello Bill,
Jerry here W0PWE in Iowa. I save up your podcasts and listen to them when I travel. A year or two ago you and Pete got me interested in the BitX and I finally took action. I have plenty of other
projects I should finish but boy was it ever fun to start a new one. This morning I soldered the
last part in my newly hatched Bitx, drug it over to the operating position and had two great QSOs
with it. See attached photo shows the rig as it was during those QSOs.

When I finished my first QSO with W9SX, Keith in WI N6ORS called me. He was running a multi-band Bitx he had built and we had a great HB2HB qso. Awesome!

My rig is scratch built, mostly SMT and generally follows the 40M schematic that Farhan has on
his HFsignals page. I am using the Kopski/Hayward TIAs though and I designed a 6 pole crystal
filter for it since 6 of the 10 crystals I bought were very similar when I characterized them
with my PHSNA setup. It uses the Adafruit SI5351 board and I modified a sketch that LA3PNA wrote for the Arduino. 

I designed and fabricated the boards for it using the software and process described by K7QO and
W5DOR. Toner transfer with the Hammerhill Gloss paper is working great. The heatsink on my IRF510 is a little light. I could smell the MOSFET warming up during a few of my lengthy transmissions with Keith.

Now the SWL report. While listening on the receiver portion of my Bitx last week I heard you on
7260 at about 0030Z. I think that was Tuesday or Wednesday. I wished I could give you a call but
at that point my PA was merely a few traces on the computer screen. Hope to hear you again on

Jerry - W0PWE

Thursday, January 19, 2017

AB1YK's FB "Al Fresco" Scratch-Built BITX 20

Mike AB1YK built this very nice BITX20.  On a board, al fresco.  Very nice.  He provides a good write up here:


I feel obligated to defend his poor analog VFO.  Mike -- that oscillator never had a chance OM!   You need to nail that coil and that capacitor down!   You threw in the towel and went over to the dark side way too fast.  Go back and get that VFO stable. 

Similarly, I'd say it is time to put away the keyboard and get out the microphone. This is a 20 meter phone rig after all.  Allow it to send your dulcet tones across the seas!

But seriously, great job Mike.  There are very few scratch-built homebrew SSB rigs on the air these days.  Congratulations OM.

Wednesday, January 18, 2017

N8NM's SAVED VFO 30 Meter Rig

In early December Steve Murphy N8NM picked up this "mystery box" at a hamfest.   Dr. Juliano identified it as an old CB VFO.  Even though Steve is deeply committed to the dark side of frequency generation (digital synthesis) I was able to convince him to put this VFO to legitimate and proper amateur radio use AS AN ANALOG VFO.  I mean just look at that dial!  It would be a sin to connect that beautiful mechanism to a rotary encoder.   We see the results below.


The 30m rig that I had hoped to have QRV for SKN is finally ready to hit the airwaves!  I still have a few odds and ends to tidy up, but it's essentially done.

Where I ran into problems was my original choice of IF and VFO frequencies: I'd gone with a 13.51 MHz IF because I had the rocks, but that put the 3rd harmonic of the VFO right in the middle of the band.  Oops.
Moving the IF to 13.56 fixed that problem, but I still had a spur from that harmonic that needed to be filtered.  At first, it looked like a trap on the output of the VFO would squish it, but it ended up requiring a few extra poles of bandpass filtering to get it below -40 dB/c.  Now we're legal.
Anyway, here's a few pics. The chassis are bent from 22 ga aluminum on my trusty Harbor Freight brake.  They're almost square, they look cockeyed because I still need to make brackets to hold the top and bottom together.  The heat sink is overkill for 5 watts, but it was cheap :-)
Electronically, almost everything between the audio and power amps is straight-up Bitx.  The power amp uses a RD16HHF1 driven by my spin on Farhan's RF-386, and the audio is an LM380 driven by an LM324, with gating between CW and digital mode input handled by a CD4066.  The CW tone generator is based on WB0RIO's "clickless" sidetone circuit, which, while a little complicated, creates perfectly formed CW elements that really sound nice.
I'm still amazed at the stability of the LC VFO; I was monitoring JT65 signals over the weekend and noticed zero drift after warm-up.  To keep it ready to rock, it's powered from the "hot" side of the on/off switch, as is the CW oscillator. 
I can't think of much else to say about it...  It is what it is :-)
73 - Steve N8NM

Monday, January 16, 2017

Of Waterfalls, SDRs, and Homebrew Analog Rigs: Words of Wisdom from W8JI


It happened again today. Conditions were good and I was BOOMING into the NYC area on 40 meters.  40 over.  Everyone liked the signal and said it sounded great.  Except for one anonymous grump who chimed in to say that I was "9 kc wide."  I imagine he was basing this on a quick look at his super-dooper SDR waterfall, without any consideration of signal strength or the characteristics of his own receiver. Sigh.  The Waterfall Police had struck again.  

OM W8JI gives a great description of the pitfalls of this kind of "you're-too-wide-because-my waterfall-says-so" reasoning.  Check it out.  And keep it handy in preparation for your next encounter with the 40 meter Waterfall Police.  


Sunday, January 15, 2017

Wonderful "QSO Today" Interview with Ian Keyser G3ROO


I knew it was going to be a good Sunday morning in the shack when I saw that Eric 4Z1UG had posted an interview with Ian Keyser G3ROO.   This wonderful interview brought back memories of my visit to G3ROO's amazing facility in Dover.  (Thanks to Tony Fishpool who brought me out there.)

In this interview, you will hear Ian state -- in a very nonchalant English way -- that he built his first receiver at age 8.  And I really loved the story of how Ian got his call sign.  FB Ian.  

Ian is a very prominent member of the G-QRP club.  I was oddly relieved to learn that he is working on a LEGAL LIMIT LINEAR AMPLIFIER.  I hope he has special dispensation from Rev. George Dobbs.  I intend to cite this project if we ever have to defend Pete Juliano from charges of QROism.

Listen to the interview here:

That is a key designed for use aboard a hydrogen balloon.  This is the kind of thing that Ian has in his shack.
This is Ian's variometer -- mentioned in the interview.

That's me using one of  Ian's spy sets. 

Ian's antenna book:

Here are the SolderSmoke Daily News posts about Ian and the Dover Construction Club:

Saturday, January 14, 2017

BITX40 to BITX40 In Australia -- Both Rigs on the Beach, Video at Both Ends

There is so much great homebrewing going on down-under.   It makes me jealous.  And so much of it is for phone.  FB.

I really like VK3YE's sand graphic proclaiming to the world (or at least to the beach!) that a BITX40 to BITX40 contact had been made. 

Looks like both rigs were using VK3YE's ceramic resonator mod for the VFO.

Be sure to check out the BITX 40 Mods blog:

Thursday, January 12, 2017

N6ORS's Franken-SDR Superhet

Of course, I love it.  MOSFETS!  NE602's!  10.7 Mc IF cans!  Cycles, not hertz! And a Tayloe Quadrature Sampling Detector made from junkbox parts from the Reagan administration. FB Keith.   And the frequency display is icing on the cake.  


I thought the group might find my new Franken-SDR interesting.
It is an SDR with a superhet front end. 

I wanted to play with an SDR but I didn't want to get a kit or buy
parts, so I scrounged through he drawers and found a mux chip
cd-4016 circa-1980 some old 7400 logic that is probably per-1980.
This could make a QSD but only very low frequencies. Well I thought
how about at IF frequencies?

The frontend is a MOSFET mixer (1975) , the 10.7 IF is a dual gate MOSFET
(1975), the second mixer is a NE602, the IF cans are all stagger tuned to
give a bandwidth of 50kcs.
The only thing modern is the DDS but I old-time-ifyed it with BCD switches.

Keith N6ORS

VK6FTH did something similar: http://www.vk6fh.com/vk6fh/SDRradio.htm

Tuesday, January 10, 2017

Understanding the "O" (organic) in OLED

That's the one I'm using.  Less than 1 inch on each side.  No back light.  8 bucks shipped:

Here is a thorough description of the technology:


Sunday, January 8, 2017

Boatanchors! HT-37 to HT-37 contact with W1ZB

Jerry W1ZB and I met up on 40 a week or so ago.  He was running a Hallicrafters  HT-37.  This spurred me to clear up the T/R problem that had knocked me out of the competition on Straight Key Night  (I'm sure I would have won!).  One spray of DeOxit D5 on the HT37 relay contacts was all it took.  Jerry and I set up a schedule for this morning on 40 minutes.   Above you can see a short video of the first part of our HT-37 to HT-37 contact.

Jerry has an amazing collection of beautiful old tube radios.  Check out his QRZ.com page:

BTW:  Speaking of old rigs talking to identical old rigs:   Last night on 40 I worked TI2NF in San Jose, Costa Rica.  He was running a Collins KWM-2 to a Collins 30-L1.  It was real nice to talk to somebody who was using an unusual rig.  Right after we finished, VE3OCZ called  TI2NF.   VE3OCZ was ALSO running a KWM-2 to a 30-L1.   TRGHS.  

Saturday, January 7, 2017

Great Interview with Farhan Re BITX 40 and BITX History

W5KUB has a really good interview with Farhan.  There are several spots where the Skype connection gets quite choppy, but hang in there -- it gets better.  Farhan provides a lot of good info on the history of the BITX rigs, his design philosophy, and the importance of the EMRFD book.  He also talks about how the BITX 40 Module is produced.  And he talks a bit about possible future rigs.  Great stuff. 

I was very pleased to hear that Farhan is trying to eliminate the need for his FT-817 (he currently needs it for its general coverage receiver) so that he can have a completely homebrew hamshack.  FB! 

Friday, January 6, 2017

NE602 Si5351 OLED "Whole Foods" Receiver

This is one of those projects that sort of just happened.  First I built an Si5351/Arduino synthesizer with a small OLED I2C display (program by Thomas LA3PNA -- thanks Thomas).  Tom Hall AK2B up in New York helped me get the Si5351 VFO and BFO going -- thanks Tom.  Then, over the holidays I decided to build a rig of some sort around the Si5351.  I started with a superhet receiver using an NE602 as the mixer and another as the product detector.  I power the NE602 with an 8 volt regulator from W8NSA -- thanks Jim.  I made a 4 crystal 11 MHz Cohn filter using crystals left over from a BITX project.  The software from AADE helped me design the matching networks to match the filter to the 1500 ohm impedances of the NE602s.   I built the circuits on a milled board sent to me by Pete Juliano N6QW -- thanks Pete!   I put a dual tuned circuit at the front end, going into a MOSFET RF amplifier.   For audio amp I have an LM386.  The whole thing is screwed down to a barbeque grilling plank from Whole Foods -- thanks Whole Foods!  (This seems appropriate -- the "O" in OLED is for "Organic"!)

It sounds nice.  I may eventually try to put some relays in to switch the NE602s and the filter around to make this a transceiver.

Monday, January 2, 2017

Straight Key Night -- Bandscan from WA6ARA (audio)

WA6ARA SKN Station
Mike Herr WA6ARA was on 40 meters with old gear this Straight Key Night.   Mike was receiving with a venerable Heath HR10B.  One of his favorite QSOs was with Keith W6SIY; Keith was running Conar twins that had the kind of "swing" that stirs up the kind of memories that SKN is all about.  FB.  Mike made a bandscan recording of what 40 sounded like, and he made another of W6SIY's beautiful signal.

You can listen by clicking on these links:  



My own SKN effort was cut short this year by technical difficulties.  The HT-37's relays stopped doing their thing.  Probably the relay drive tube going soft.  But I did manage to make two great contacts on 40:

WA6URY is in Los Angeles.  This was a very timely contact -- my wife and I went to see the movie "La La Land" on New Year's eve -- the film features a lot of beautiful LA scenery.  Dan was running a kilowatt to a 2 element Yagi on 40.  He too owns an HT-37 and a Drake 2B.  He was on a straight key "with dirty contacts."  FB Dan, thanks.

And then I worked W1PID!  Wow! Jim is well known for his operations from field locations and for his intrepid participation in many of the radio adventures of Michael Rainey AA1TJ.  Jim was on the Maine sea coast expedition when Michael was attempting to cross the pond with his voice-powered radio.  On SKN Jim was in New Hampshire running 35 watts to a Windom off-center fed dipole.  His Morse key is a Kent.    TRGHS.   Thanks Jim.

Happy New Year!

W1PID Maritime Mobile

Designer: Douglas Bowman | Dimodifikasi oleh Abdul Munir Original Posting Rounders 3 Column