Schematic for the RTL SDR Dongle Front End

Here it is.  Very simple.   I used an obsolete 40673 dual gate MOSFET.  I didn't need both gates so I just soldered them together. You could probably substitute an easily obtained MPF-102  JFET.  The capacitors and the coil in in the gate circuit form a parallel LC filter circuit that resonates in the 40 meter ham band.   The 1 Megohm resistor maintains a very high impedance for the LC circuit, helping to maintain circuit Q (sharp response).  It also drains off any charge that builds up on the gates.  For the antenna input I just put 2 turns on the 4.5uH coil -- this too helps maintain LC filter response.  The 470 ohm resistor serves as the load and limits quiescent current through the MOSFET.  It should pull about 19 milliamps -- with a 9V battery that should give you around 26 hours of listening time between battery changes.  That's fine with me -- I don't use this thing that much. 

Realize that I'm using this with an RTL-SDR dongle that has been given the familiar modification that allows it to use direct sampling in the HF bands.   Some ideas here:

http://www.rtl-sdr.com/rtl-sdr-direct-sampling-mode/

and here

http://soldersmoke.blogspot.com/2015/04/sdr-dongle-modified-for-hf-watch-it.html

and here

https://dl.dropboxusercontent.com/u/1987387/Even_more_on_using_the_RTL2832U_Dongle.pdf

Adding a Homebrew Front End to an RTL-SDR HDSDR Receiver

I started playing with the RTL SDR dongles again.  I wanted to use them to confirm that my BITX signal is NOT 9 kc wide (it is not).  I also wanted to try to confirm the aircraft band frequencies in use in this area.

So I got the HDSDR software running and plugged in the dongle that I had modified for HF use.  It worked great, but I could see (literally SEE) that it needed some bandpass filtering and perhaps a bit of RF gain.  So today I threw together this device.  Dual gate MOSFET (gates tied together) with an LC filter on the gate.  Power from Malaysia via the 9V battery.

It works great. It was fun to add a bit of homebrew to an otherwise soul-less commercial receiver.   But beware: that waterfall is addictive, even for a hardcore Hardware Defined Radio guy like me.

"First Light" on Brad's Direct Conversion Receiver

So cool.    You can just feel the enthusiasm.  Congratulations Brad!

Bill and Pete:

After 63 years, I was finally able to build a DC receiver of my own design.  We achieved "first light" at 7:20P last night.  I attached the antenna, speaker, then applied power - and a all of a sudden "Bob's your uncle!!"  There are some things I still don't quite understand but right now none of that matters as I listen to the sound of clean, crisp CW pouring out of the speaker and filling the room!!  Major components - SI5351, SBL-1, TL072 op amp bandwidth filter, LM386 audio amp.  I plan to use clk2 of the SI5351 with some Arduino code to create the companion transmitter and CW keyer.  Life is good!!!

Brad WA8WDQ

W8LM's BITX on a Board

The purpose of the BITX40 project was to encourage modification, experimentation, and more frequent melting of solder.  I think these pictures from W8LM serve as yet another reminder that this goal is being achieved.  The contrast with the big appliance rig in the background is, in so many ways, striking. You'd be understandably reluctant to take a soldering iron to the commercial rig, but the BITX seems to be crying out for hot iron and solder smoke. 

W8LM wrote (on the BITX20 group):

Guys- Here are pix's of my BITX40 fired up today in Receive for testing. #1 I have the tuning clicks- so I will be debugging that. #2 shown in the pictures is my test of calibration which was not necessary. I used a T and put my ICOM 756proII  and the BITX40 on the same antenna (a Windom flat top at 33Ft)  The display of both read 7.1700 pretty much the center of the band and I was copying 4's,8's and 2's at 23:30zulu) By moving volume controls up and down I could listen to both rigs same frequency, audio comparison acceptable. An AGC circuit is in order.  The mylar-plastic cone of the surplus speaker lacks fidelity. Unfortunately the 16x2 display did photograph well. It's a start-- de W8LM

A Mighty Mite, a BITX40, an ILER, some Arduinos, and the Joy of Oscillation in the United Arab Emirates

Martin A65DC sent us this wonderful report on his efforts in the UAE.  His e-mail nicely conveys his enthusiasm.  I was especially pleased to see that wooden enclosures are catching on (another fellow on the BITX20 group is using a cigar humidor).  Thanks Martin!  Please keep us posted on your UAE homebrew adventures.

Hi Bill and Pete,

My name is Martin, and I am listening to every episode, sometimes more than once, thank you for an excellent show boys. I am a ham in the United Arab Emirates and operate radio as A65DC.

I just wanted to share my "JOY OF OSCILLATION” moment with you, I had the moment two days or so ago.. fantastic!

Well it is not super tidy, but as a proof of concept is totally acceptable. red and green goes to the variable cap (above).

Next to the Mighty Mite (above) is my bitX40, what a fantastic board!! I have big plans for this radio. But for now it will stay in its wooden box and keeps me company.

This (above) is another kit build, 20m SSB kit from EA3GCY Javier. ILER20, please have a look, this is where you should start if you are into kit building!! the instructions are fantastic.

I added some Arduino magic to it with a SI5351, and then I was sitting and looking at my big UNO board, hmmm USB port, why not further develop the code and use the port as CAT control.

I can now connect this rig to e.g. N1MM and control it, read and write frequency (in current version) I am simulating the protocol of a TS590, but that turned out to be a bad choice, I should have gone for a simpler radio, like a 140 or something, the 590 has loads of CAT commands that my code needs to answer… this radio is my QRO 20m as rig it sports the 20w amplifier kit from K5BCQ and will put out a whooping 22w!  Several contacts from A6 into Europe and some over to Indonesia.. fun stuff, two kits from different vendors together with some own building and coding.. I love it.

On the workbench now is an Arduino CW keyed based on K3NG, the Arduino code is very well written and it has loads of functionality, most of what I will never use.. but as a keyer it is superb.

This is my keyed circuit, super simple stuff, it is here connected to the Mighty Mite as a test, works 100%  I am now researching a good circuit for a CW transmitter/transceiver for 40m that will be in the 5 to 10w range to use my new keyer with.

Again, thanks for a fantastic show guys,

73

A65DC, Martin

Colin M1BUU Achieves SOTA "Mountain Goat" Status -- With Rig Built ON THE MOUNTAIN TOP

Stiff upper lip OM!  MUSN'T GRUMBLE and all that...

Our friend and BITX builder Colin M1BUU has opened up a new area for ham radio masochism:  EXTREME MOUNTAIN-TOP RIG BUILDING.  That's right my friends.  You read that right. Colin has taken the solder smoke to new heights.   Soon,  these guys will be pouring scorn on those of us using "shack built" rigs.  Congratulations Colin!   Well done! 

Colin's write up from http://reflector.sota.org.uk/t/colin-m1buu-mountain-goat/14559  :

The general story goes something like this -
I started with SOTA way back in 2004, aged 24. Just after I found SOTA, I also found love - Fiona and I will celebrate our 10th wedding anniversary in April. You know how the story goes..........
Winter time has generally been quiet in terms of family stuff, so it's generally this time of year when I activate, usually January to March.
You've heard of extreme ironing, right?

en.wikipedia.org3

Extreme ironing

Extreme ironing (also called EI) is an extreme sport in which people take ironing boards to remote locations and iron items of clothing. According to the Extreme Ironing Bureau, extreme ironing is "the latest danger sport that combines the thrills of an extreme outdoor activity with the satisfaction of a well-pressed shirt." Part of the attraction and interest the media has shown towards extreme ironing seems to center on the issue of whether it is really a sport or not. It is widely considered t...

Being a prolific builder of radio kits, I thought I would do my own twist on Extreme Ironing - Extreme Solder Ironing!
Today was the day. I took a RockMite kit, a home made key kit and a home made vertical antenna kit up to the summit of Whernside G/NP-004. I assembled the kits using a gas powered soldering iron. Thankfully I took my little tent with me, the weather wasn't exactly tropical.
The kits went together well and the RockMite fired up first time without any debugging, although the building took much longer than I had reckoned.
I was late on air, but eventually Barry N1EU found me for my first contact. Shortly after followed SP9AMH, OH9XX and finally EU2MM to earn me my needed points. Mountain Goat was in the bag! The QSB was very evident today, QSO's were tough, except with OH9XX, who was ear blasting.
Firing up the FT817 (I intended to share my success with as many as possible!), I worked a handful more stations on CW and SSB, but my time was rapidly dwindling.

Finally, I'd like to say thanks for all the support given by numerous SOTA participants over the years, There's a number of great, inspirational people we've lost in that time and I think about lots of them all the time. Roger G4OWG was particularly on my mind today as I learned of the route I took today from one of his posts. I never met Roger in person, but he was a keen chaser and fairly local to me.
73, Colin
Edit - I forgot to put forward my thanks -
Thanks to Dennis G6YBC (Kanga Products) for sponsoring a RockMite ][ ver. 1 PCB
Also thanks to Pete G4ISJ for supplying the solder!

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

SolderSmoke 193   28 Jan 2017

http://soldersmoke.com/soldersmoke193.mp3

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:

Pete:
-- Color Displays!
-- KWM-4
-- OLED MADNESS!

Bill: 
-- 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.
-- BANDSWEEP
-- 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.

LEXICON:  HAYWIRE   TOMBSTONE    BIKESHEDDING from Todd K7TFC

Some great recent interviews by Eric 4Z1UG:
Ian G3ROO  Origins of ROO   Regen at age 8
Hans Summers G0UPL     Balloons!   NO COMMECIAL GEAR
David White WN5Y          ELECTROLUMINESCENT  RECEIVER EXPLAINED
Rob Sherwood NC0B 

MAILBAG: 

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:

 http://www.sarl.org. za/public/local/GoogleRepMap. asp?Lat=S%2026%2011%2008&Lon= E%2028%2008%2049

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:

www.facstaff.bucknell.edu/dkelley/elec351/Lab/elec351lab5_sp04.doc

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:
http://www.rowetel.com/?p=4781

KD4PBJ's FB BITX 40

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

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:  

http://www.arrowantennas.com/sub/hambrew.html

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
40M.

73/72,
Jerry - W0PWE

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:

http://n1fd.org/2017/01/18/first-homebrew-contact-on-my-scratch-built-bitx-20-ssb-transceiver/

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.