Using the RF Power Amplifier of the BITX40 Module

 

PA shematic from the BITX 40 Module

Click on the diagram for a better view

C.F. Rockey W9SCH (who alerted us in SPRAT 22 to the chicken sacrifice option) spoke of transistors that exhibit "quantum mechanical necromancy."  Rockey explained that when this happens, "The transistor simply turns up its toes and dies. Not even an Atomic Physicist can tell you why!"  

This often (very often!) happens with homebrew power amplifiers.  So when we find a good one, many of us stick with it, using the same power amp circuit in rig after rig.  I have done this with the power amplifier from the BITX40 Module. 

Mythbuster (75 & 20 Meter) version (early)  

Click on image for a better view. 

https://soldersmoke.blogspot.com/2021/08/mythbuster-video-13-rf-power-amplifier.html

Same amplifier built into Version 2 of the 15-10 Transceiver 

Click on image for a better view. 

In the build for the 15-10 transceiver you can see some changes.  I used an RD06HHF1 instead of an IRF-510.  I used an 8.1 volt zener diode instead of the regulator chip. I set the bias at around 5.5 volts DC on the gate of the RD06.   I used a smaller, metal can driver transistor (it works fine). I changed the input/output physical configuration between the pre-driver and the driver stages (I think it was kind of goofy the way I had it in the Mythbuster).  Finally, you can see how I used a small piece of copper tape (with conductive adhesive) to shield the line going from the driver transformer to the gate of the RD06.  The wire was too small to use a bit of shielded coax, but I think the copper tape and the copper clad board beneath it work just as well. 

Farhan provided me with some fascinating background on this circuit: 

Bill,

I just saw your post on the bitx40 power amp. The credit must go to Wes for this, it is from the Lichen transceiver described in 6.9 of the EMRFD. I merely copied it with some modifications for it to work with junkbox components.

It bears mentioning that at that time I didn't have a way of generating two tone signal or measuring the IMDR. Those came later when I built my own spectrum analyzer based on Wes and Terry White's spectrum analyzer. It was sheer luck that I picked this power chain that already had careful gain distribution.

For the output, the original build used and LPF with inductors wound on a ballpen shell and TV baluns cores instead of toroids. Again, it was incredibly lucky that they worked at all. 

- f

Justin's Receiver -- A 40 meter Superhet from AC8LV

 

FB Justin!  I really like the board that you are using as a base for the project.  And you have some great mentors in Nick and Loren.  

It is wonderful that you have that receiver working.  But I would tweak and peak quite a bit before taking on the transmitter.  Get a decent outside antenna -- even a dipole or a 1/4 wave with counterpoise would be a big improvment.  Like this one:  

https://soldersmoke.blogspot.com/2023/03/an-antenna-for-high-school-direct.html

And try to square away the grounding on the board (maybe some copper tape from Amazon) and the power supply you are using (I hope it is not one of those noisy wall warts).  When  you are experimenting, it can be useful to power varous stages with 9V batteries -- this is a good way to find out where noise is coming from.  If your AF amp is squealing at 12 volts, you need to break the feedback loop that is leading to oscillation.  Often the feedback is through the power supply.  Finally, try to get that homewbrew crystal filter working -- if the bandpass is uneven, you just need some impedance matching at the input and output.  

Great work Justin!   Keep at it.  73  Bill 

Bill,

I am sending video and pictures of my 40m  superhet that I built. I have it on the floor in an extra room in the house. The antenna is a stock vhf dipole that came with my rtl sdr which I use as a spectrum analyzer. In one of the clips I am receiving RW7K. I have been working on the station for the past year with help from Loren Moline, WA7SKT through texts when I have a problem. The LO / VFO is from Nick Woods Videos.

Next, I will build an outdoor antenna and the transmitter section. I first started homebrewing at the beginning of the pandemic, but this is by far my largest accomplishment. I would like to thank you and Pete for the soldersmoke videos which have been a great inspiration.

I will send more updates when the transmitter section is finish along with a much longer description of the projects

Thank you

Justin Elliott
AC8LZ

Bill, Pete, and Dean 

Thank you for the compliment. Pete, I want you to know, I’m a huge fan and I enjoy the one-liner jokes. I enjoy your contributions to the videos when you’re on Dean. 

Here are pics / videos of my superhet. 

The bandpass filter is a homebrew version of qrp labs design for 40m, I had to add an extra capacitor to get the bandpass where I wanted it. It is 6.9mhz to 7.32mhz. 

Mixer / demods are ade-ask.

The rf amps are kits i bought online, assembled, then used the schematics to replicate. They are the W7OI created and which have been mentioned on the channel

The LO/VFO are arduino driven from Nick Woods (M0NTV) YouTube channel. I believe episode 26

The crystal filter was built for 9MHz, but when I swept it I found the bandpass was saw toothed, so I used a commercial filter that Loren Moline WA7SKT sent. 

The audio amplifiers are a Common Emitter Amp I found on YouTube, I can’t recall the channel and a commercial amplifier, which I can now reproduce as I have the schematics. 

The speaker is a 2W 8 ohm speaker. 

...

Justin Elliott

AC8LZ

Radio Items Picked-up at VWS Winterfest 2024 Hamfest

As always, click on image for a better view

Above you can see what I picked up at the Vienna Wireless Society's 2024 Winterfest Hamfest. 

-- On the left in the blue box is an MXM Industries SuperRX/TX 40 transceiver. It is a kit from a Texas company.   Superhet receiver with IF at 455 kHz.  Crystal controlled CW transmitter on 7040 kHz.  The oscillator works, but so far no receive signals.  I will have to troubleshoot.  Does anyone have a schematic? 

-- Behind the MXM there is a nice box marked "Diode Detector" I opened it up and there is just a solid state diode and a 50 ohm resistor to ground.   Box may be useful. 

-- I got a couple of books: "Weekend Projects" 1979 from ARRL, and "A History of QST -- Volume 1 Amateur Radio Technology 1915 - 2013" 2013 from ARRL. 

-- On top of the Weekend Projects book you see a "Crystal Holder" from Gross Radio of New York City.  W1UJR has some good history on this company:  https://w1ujr.com/written-word/gross-radio-company-circa-1931/  This device seem to be intended to hold in place a raw piece of quartz!  Cool. 

-- To the right of the books there is a serious-looking VFO.  One dollar!  Deal!  It is a CB VFO, but the markings say it puts out 5.44 to 5.99 MHz.  So it should be useful.  The dual speed dial is very nice.  

-- Above the VFO is a nice step attenuator from the "Arrow Antenna" company of Loveland Colorado. 

-- Further to the right are some Electric Radio and Antique Wireless Association magazines that Armand WA1UQO gave me.  Really nice.  The AWA mags have a very thoughtful piece (warts and all) on Jean Shepherd.  And the ER pile has an article by Scott WA9WFA that mentions my work on the Mate for the Mighty Midget receiver.  Thanks again Armand! 

-- I also got some ADE6+ surface mount mixers.  The price was right! 

Thanks to VWS for putting on this great hamfest! 

The Wizard of Schenectady -- Charles Proteus Steinmetz

Such a beautiful article.   Ramakrishnan VU2JXN sent it to me.  It reminded me of how puzzeled we were when we found "Schenectady" on old shortwave receiver dials, amidst truly exotic locations.  Rangoon!  Peking!  Cape Town!  Schenectady?   Obviously this was due to General Electric's location in that New York State city.  But reading this article, I am thinking that the presence of Charles Proteus Steinmetz had something to do with it. His informal title (The Wizard of Schenectady)  confirmed that we have been right in awarding similar titles to impressive homebrewers. 

Here is the Smithsonian article that Ramakrishnan sent. 

https://www.smithsonianmag.com/history/charles-proteus-steinmetz-the-wizard-of-schenectady-51912022/#ixzz2lRMjrfit

And here is a link to a PBS video on Steinmetz: 

https://www.pbs.org/video/wmht-specials-divine-discontent-charles-proteus-steinmetz/

Here is a SolderSmoke blog post about "Radio Schenectady":

https://soldersmoke.blogspot.com/2020/07/radio-schenectady.html

N6ASD Builds a Zinc-Oxide Negative Resistance Transmitter (and a Spark/Coherer rig)

I saw this video and post on Hackaday this morning:

https://hackaday.com/2024/03/05/making-a-crystodyne-radio-with-zinc-oxide-and-cats-whiskers/

I got the fellow's callsign from  his Morse CQ.  

It is N6ASD in San Francisco. 

Check this out from his QRZ page: https://www.qrz.com/db/N6ASD

My journey into the world of amateur radio began in a very primitive way. My first "rig" comprised of a spark-gap transmitter and a coherer based receiver. A coherer is a primitive radio signal detector that consists of iron filings placed between two electrodes. It was popular in the early days of wireless telegraphy.

Spark transmitter (using a car's ignition coil to generate high-voltage sparks):

Coherer based receiver (using a doorbell for the "decoherer" mechanism):

When I keyed the transmitter, a high voltage arc would appear at the spark-gap and this produced (noisy) radio waves. The signal would be received by the iron-filings coherer on the other side of the room. A coherer is (usually) a one-shot receiver. You have to physically hit it to shake the filings and bring the detector back to its original state. That's what the doorbell hammer did. It would hit the coherer every time it received a signal. It amazed me to no end. A spark created in one room of my house could make the hammer move in another room. Magic!

Soon after this project, I started experimenting with *slightly more refined* crystal detectors and crystal radio circuits. As most of you would know, these amazing radios don't require any batteries and work by harnessing energy from radio waves. I guess these simple experiments instilled a sense of awe and wonder regarding electromagnetic waves, and eventually, this brought me into the world of amateur radio in 2015.

My main HF rig is an old ICOM IC-735. The only modification on this is radio is that it uses LED backlights (instead of bulbs):

With space at a premium in San Francisco, the antenna that I have settled for is an inverted vee installed in my backyard (and it just barely fits). I made the mast by lashing together wooden planks. For this city dweller, it works FB:

I have recently gotten into CW, and it has definitely become my mode of choice.

I'm a self-taught electronics enthusiast and I love homebrewing radio circuits. I'll be sharing more info about them soon.

Thanks for checking out my page. I hope to meet you on the air!

73,
N6ASD

 

A Contact with my Old Azorean DSB Transceiver

I've been thinking about balanced modulators, and I wanted to see how some of my early circuits performed.  So I pulled this OLD Double Sideband rig off the shelf and fired it up. The balanced modulator -- and everything else! - worked fine,  and I soon made contact on 17 meter SSB with Gene, AB9GK. 

This was the first DSB transceiver that I ever built.  I made this out in the Azores, probably in 2000 or 2001.  Years later I had replaced the RF power amplifier with a "JBOT" (Just a Bunch of Transistors) designed by Farhan.  

Over on my YouTube channel a comment came in from my friend Jack:  

@dhakajack

"Looking inside and seeing the o-scope probe in place while the radio was on the air reminded me of neurosurgery where the patient is awake and talking while the surgeon probes different brain regions soliciting feedback. Sure, ham radio isn't neurosurgery, but it's not too far at times. Also, you already have rocket science covered."

Here is an article about my build of that first rig:

https://www.gadgeteer.us/17METER.HTM

I think the article captures well the trials and tribulations faced by new homebrewers, perhaps with the twist that comes from being out in the middle of the Atlantic ocean.  

Mike WU2D is having similar fun with his homebrew 10 meter DSB transceiver: 

https://www.youtube.com/watch?v=uZt1LTGyoHc

I was struck by how similar Mike's early QSO experiences were with mine.  We both put our DSB transmitters on the air before they made their way into real cabinets or boxes. 

Here's mine from 2001 in the Azores: 

Innovation and a Dual Band Sweep with Version 2 of the 15-10 Transceiver

Here are a couple of videos on Version 2 of my 15-10 SSB transceiver.  In the video above I try to show the advances and innovations that have been made since the start of my BITX construction adventure back in 2013.  

 The video below shows the receiver in action this morning on 15 and 10 meter SSB.  I think it sounds pretty good. 

Click on the image for a better look

Farhan asked what the passband of the 25 MHz crystal filter looked like.  I sent him this.  I think it looks very good, and shows that it is possible to use an IF this high.  This permits us to not only set up the transceiver for dual band coverage (in this case 15 and 10 meters), but it also allows for a lower frequency VFO (in this case around 3.5 MHz) with a resulting increase in VFO stability.  

More on "Kludge" -- Merriam-Webster's Pronunciation Guide

 https://www.merriam-webster.com/dictionary/kludge

What say our British cousins?  How do you pronounce the word? 

Kluge as in huge? 

Kludge as in fudge? 

Innovations and Inventions in Garages and Basements

The Hewlett-Packard garage

There is a lot of inspirational stuff in this blog post, especially for those of us who work in home workshops, often in garages or basements. 

https://www.strangeloopcanon.com/p/the-mystery-of-the-garage

Thanks to HackaDay for alerting us to this. 

Some of my Double Sideband Rigs: Azores, Virginia, Dominican Republic

The above video describe a round of mods to the much modded DSB rig. And my alleged winning of the ARRL Sweepstakes (in a very elite category). 

The video above shows where I took the rig in 2014.  Bahia Rincon, Samana peninsula, Dominican Republic.  You can also see my power supply. 

Here is an article on the first DSB rig that I built, out in the Azores:  

https://www.gadgeteer.us/17METER.HTM

I think the article captures well the trials and tribulations faced by new homebrewers, perhaps with the twist that comes from being out in the middle of the Atlantic ocean.  

Mike WU2D is having similar fun with his homebrew 10 meter DSB transceiver: 

https://www.youtube.com/watch?v=uZt1LTGyoHc

I was struck by how similar Mike's early QSO experiences were with mine.  We both put our DSB transmitters on the air before they made their way into real cabinets or boxes. 

Here's mine from 2001 in the Azores: 

The Mars Helicopter and its CO2 Insulation

This video isn't about homebrew ham gear, but nonetheless I found it very interesting.  Of particular interest is the bit about their need to find a very low-weight insulator to protect the instruments from the cold of the Martian night.  Aerogel would have been too heavy.  So they just filled the instrument chamber with Carbon Dioxide.  That was their insulator. Think about that, especially those of you who still deny CO2's ability to heat up the atmosphere.  

There is a lot of great stuff on Veritasium's YouTube  channel:  

https://www.youtube.com/@veritasium

Grayson Evans KJ7UM Video on Homebrewing with Thermatrons

Grayson Evans KJ7UM is the author of Hollow-State Design for the Radio Amateur, a wonderful book about using Thermatrons (aka tubes, or valves) in radio projects. Buy it here:

https://www.lulu.com/shop/grayson-evans/hollow-state-design-3nd-edition/paperback/product-5mpzqr.html?page=1&pageSize=4

More info on the book is here: https://kj7um.wordpress.com/2020/12/02/hollow-state-design/ In this video, Grayson talks about construction techniques (including the use of Thermatron Me-Pads), and Manhattan construction for Thermatron projects. FB! Visit Grayson's blog: https://kj7um.wordpress.com/