First QSO with the Ten Minute Transmitter

At the recommendation of Bill Maera (N2CQR), I used the SKCC scheduling page to get someone to meet me on frequency for a QSO. Wish I had a video, but here's the log entry:

K8JD (Commerce, MI)
Bearing: 312°, 711km/442mi
SKCC Nr 1395
7.1228 MHz
19 May 2021
2330-2334 UTC
Sent: 559
Recd: 529

Lots of adjacent phone conversations on LSB, but not bad at all for little 360 mW wonder....

Ten Minute Transmitter On The Air with a Homebrew Antenna Switch

Why I need This

My Ten Minute Transmitter is just that--a transmitter. It is not a receiver. To get on the air, I have to:

• Connect to a suitable antenna
• Listen to any reply using a receiver or transceiver

Since I have few choices of antennas, my transmitter will need to share the same antenna as my receiver. (In this case, my receiver is a KX3). And to use the same antenna, I need a switch that opens the connection to my 40M antenna when I'm transmitting, then close the connection to the transmitter and open the connection between the 40M antenna and my receiver. 

Resources

An antenna switch doesn't sound that complicated. I wondered if I'd need to connect all the negative/shielding together. I used the following resources:

• https://swling.com/blog/tag/homebrew-antenna-switch/
• https://dailyantenna.blogspot.com/2019/02/building-manual-hf-antenna-switches.html
• https://pa0fri.home.xs4all.nl/Ant/ANTswitch/antswitcheng.htm
• https://www.g4ifb.com/html/homebrew.html#ManualAntennaSwitch

Information about capacitive voltage dividers are here https://www.basictables.com/electronics/capacitor/capacitive-voltage-divider In essence, I don't require a voltage divider since I'm not attempting to take readings through a scope.

The Build

I basically drilled holes on three sides of an Altoids tin for four very old BNC adapters that I scrounged from the garbage about 10 years ago. A SPST switch completed the fourth side. I used a short length of RG-8x coax to tie the hot terminals together. here's a picture:

The Result

The switch worked quite nicely after I remembered to use it! I called CQ several times. While nobody returned my call, I was spotted by Bob Delinger (KD7YZ) on the Reverse Beacon Network. (Bob is in Greenup County, Kentucky (Grid EM88ll) which is about 305mi distant. I registered a 5dB signal--not too bad since I'm putting out only about 360 mW).

Low Pass Filter Construction

Background

Next step after building a functioning transmitter: clean up the signal. 

Moving Forward

To create a Low Pass Filter, I used information readily available at the G-QRP site. A good page is the A Short Guide to W3NQN Harmonic Filters for QRP Transmitter Output. - George Dobbs G3RJV. This is a good overview, but I found the older version that I think, well, would be an easier for the time being. A copy of George, G3RJV first paper can be found here: A Complete Do-It-Yourself Kit ....... with just a few simple calculations (George Dobbs G3RJV)

Design & Build

Here's the design:

And here's my parts:

• 3 x T37-6 (for L2, 4, 6) 
• 2 x 220 pF and 47 pF capacitors. These will be in parallel for a 267pF cap substituting for the 270 pF caps for C1 & C7
• 2 x 470 pF and 220 pF capacitors. These will be in parallel for a 690pF cap substituting for the 680 pF caps for C3 & C5

Finished Product

Here's what the final product looks like:

Top Side

Underneath

Results/Performance

I listened for oscillation at 2x (14.260 MHz), 3x (21.369 MHz), and 4x (28.492 MHz). I never really heard anything on 14.260, but certainly did on 21.369 and less so on 28.492. The following video shows the test on my receiver and scope plus a quick voltage calculation on the dummy load.

Next Steps

• Finalize capacitor value
• Assemble into an enclosure. Add BNC antenna connector and 3.5mm jack for a straight key
• Make some QSOs

Moving Forward with A 40M Transmitter

The Idea

In a desire to build something to get me on the air, I've taken a step back from the 80 MMM and have decided to move forward with a 40M transmitter. Bill Maera recommended aiming at the 10 Minute Transmitter.  Quite sure this was on Bill's mind when posting Ciprian's version.

I decided to not build a low pass filter for my 80M MMM. My thinking: I'm a parts cheapskate and I really won't be using the 80M MMM to get on the air. Yeah, I wanted to see an improvement of the carrier wave on the oscilloscope, but I'll be doing this for 40M, right?

I collected some parts, ordered a few too. Bill recommended trying any NPN transistor that I had in inventory, so I'll thought I'd mock up the transmitter using a 2N2222 or 2N3094. What's the worst that can happen? I mean, there is the word "smoke" in the Solder Smoke podcast name. 

Here's the design(s) that I used:

Original 10 Minute Transmitter by Steve (G4RAW)


 

Walter (KA4KXX)'s version as seen in the Solder Smoke blog..

And here's my parts:

• 100uH coil.*
• .1uF capacitors (2)
• 240 pF capacitor**
• 7.123 MHz crystal
• 22K resistor
• 2N3053 transistor***

* Using 37-43 toroid, that's about 16-17 turns as indicated in winding data found on Kits & Parts.

**Walter (KA4KXX) has adjustment instructions on the Solder Smoke blog: please be advised that the way to tune the "240" pf series output capacitor is to first connect a 50 ohm dummy load to the transmitter and peak the RF Output Voltage. If there is no defined peak then temporarily use a variable capacitor with a wide range because your value may be much different than mine since you are using another transistor, circuit board layout, etc. Also, note that in my version I connected the transmitter to a multi-stage antenna tuner before attaching that to my end-fed antenna so my signal out of the antenna was probably very clean. . 

***Other NPN transistors such as a 2n2222 or 2n3904 should also work.

The Trouble

I breadboarded the circuit and... Nothing. Like absolutely nothing. 

Now, those who grew up in 70's and 80's remember the teen biopic The Breakfast Club. In that movie, the nerdy teen who found himself in Saturday detention reveals his biggest failure: he couldn't make a lamp in shop class. You know where this is going: I felt like that kid. The 10 Minute Transmitter That Took Two Days to Build. 

No worries. I now like to think that I'm grown up and laugh at myself, my abilities (or lack thereof), and some of life's little foibles. Be that as it may, Bill relayed some troubleshooting hints:

On this project you might need an antenna or an antenna substitute.  Just put a 50 ohm resistor from the variable cap antenna connection to ground.    Then try getting it going while fiddling with the variable cap setting. 

It should work with 9V.   But maybe try a fresh battery.  

To check the voltages -- keeping the key up, the voltage on the collector of the transistor should equal the voltage of your power source.  

If you've let the transistor get too hot, try with a new transistor. 

Make sure you have the leads right on the transistor,  It is usually E B C facing the flat part of the transistor,  It is easy to get them backwards. 

I think Walter was talking about peak output voltage.  Don't worry about that for now -- you just want to get it oscillating.   

Make sure your receiver is on LSB or SSB or CW (not on AM)  Tune around a bit as you fiddle with it. 

Peter Parker did a video on this: https://www.youtube.com/watch?v=cPPi7uLGtgY

Perhaps more useful is this: https://makerf.com/posts/ten-minute-transmitter

Hang in there.  Let me know how it is going. 

Of course, I didn't stick to one set of variables. I did several things--all or some of which may have made the difference:

1. I moved to 12v power. Actually, I used 13.8v and powered through a plug so that I could use my normal rig power supply or LiPo battery from portable operation. Pinout reminder:

 

2. Most importantly, perhaps, I ditched the breadboard. Chances are some small connection is broken or I failed to visualize a vertical connection. "Time to melt some solder," said Bill.

3. Added a variable capacitor so that I could adjust peak output at some point.

Here's what my project looks like:

And We're In Business

We're oscillating, folks:

Project Description

Successful Oscillation

Mounting to Perfboard and Scope Test

I was happy to finish out my normal duties last night (training, practice my lute, etc.) and move the MMM to a more permanent perfboard. In the case of this mounting, I did my best to preserve the layout of the schematic if at all possible. I checked continuity after mounting each component, etc. Everything seemed to be going great. But I couldn't get any signal at 3.579 MHz. Damn. Truly, I didn't beat myself up about it. Instead, i headed back upstairs after the youngest went to bed and did some reading. 

I have the circuit another look on a short work break. Tested I connected the battery and heard the slightest amount of oscillation. Hey! And I noticed significant shifts in oscillation when I fooled with the L1/L2 coils. 

Troubleshooting: I'm not sure why this would occur. I understand that touching the coil would change the inductance. Ought I need to fix this before moving forward? Exactly how would I do this?

This feedback from Bill Maera: 

Yes, or you could go with a toroidal coil   Aside from the value in uH  you have to pay attention to the tap -- and make sure that you are tapping from the correct side (usually X number of turns up from the bottom).  Try it. 

If it doesn't work, take a look at the coil and the tap.  

You are mentioned on the SS blog.   With a link to your site.<--the real cool part

I then put the MMM on a scope shown below. 

Next steps:

1. Better understand the coil issue.
2. Build a low pass filter (LPF) to pass frequencies below 4 MHz. 

I'm so pumped. I have a beer in my hand and have had a great two days of amateur radio.

I connected yesterday with Bill Maera (N2CQR) of Solder Smoke Podcast fame. He and I had been in contact for the past few weeks about how to get started with scratch building. 

Granted, credit goes to Paul Taylor (VK3HN). I saw Paul's presentation at the QSO Today Expo in mid-March 2021. Paul presented his scratch built QRP radios. Just amazing. Thought I could never do that. And I can't today. Felt compelled to learn more: how do these radio stages work? How do you figure out which capacitor value is best for this tank circuit? How? What? Lots of thoughts. I wrote Paul, eager as a beaver, and asked his advice. He told me two things: one, sit at the feat of the masters and two, start slow and simple. The masters being: Charlie Morris (ZL2CTM); Peter Parker (VK3YE); and definitely Pete Juliano (N6QW) and Bill Maera who both produce the Solder Smoke Podcast.

I wrote both Bill and Pete with this impassioned plea:

Name here is Jack Haefner, NG2E. 

I saw Paul Taylor's (VK3HN) presentation at the QSO Expo last month and was completely blown away by his work. Scratch building--at least his approach--seems very logical, throughout, and, frankly, rewarding. But I completely lack knowledge in this area.

Frankly, I am looking for advice on how to get started. Per his suggestion, I've looked at plenty of sites (Peter Parker (now there's a name) (VK3YE), Charlie Morris (ZL2CTM), and others). While there's plenty there, I just don't know where to begin. 

Now, I do have a parts bin and am not afraid to solder something up and see what happens. But I wonder if you might have advice about how to hone in on what I see as some high-level objectives:

1. I'd like to build in stages and test/understand what is going on in between each stage.

2. I'd like to build QRP/portable sets since I Iike to do some SOTAs and, well, I'd like what I build to be useful.

3. No problem starting with CW since I have passable proficiency there.

I have a multimeter, a scope (never used since, well, I wouldn't know how to use it). I'll probably buy an inexpensive inductor tester since I'll probably need to wind a few of them.

I have the ARRL Handbook (2011) and Build Your Own Transistor Radios (Quan). There are some explanations in those texts, but they accelerate pretty fast. And I've built kits (Rockmite, Elecraft KX1)--I can certainly follow directions, but, I frankly don't know what is happening under the hood.

Other than that, happy to take any ideas that you might send my way.

Pete's reply a few days letter with echoes provided by Bill:

Hi Jack,

 

Thank you for your email and I will be glad to help as best as I can. The first important point is that you have connected with some of the best homebrewers in the world, Paul, Peter and Charlie. –These truly are some of the most talented HB specialists. Charlie has several series of homebrew you tube videos that step you through a project and includes the theory not just solder tab A to Slot B. So check out his channel and work/follow along with him.

 

As for my contribution here are some suggestions:

 

1. Start with a small project that will let you take that project and learn the two salient aspects – the physical construction and the why it works. One of the best to launch that effort is a low part count (less than 15 parts with the Low Pass Filter and 8 without) transmitter called The Michigan Mighty Mite. Because it is a low part count – not expensive and it will let you understand the why it works. Other projects like this include The Tuna Tin Two from Doug DeMaw W1FB now a SK.
2. Next would be a receiver and I recommend a Direct Conversion Receiver. With these two projects you can have a working station. There are many forms of the DCR but if you look on my website you will see one using a MC1496 IC – these can be bought in SMD for less than $1. See www.n6qw.com  and this link
3. https://www.n6qw.com/MC1496.html

 

There is a video on that link and you can hear how good it is.

 

I would stay away from the $4 Pixie radio kit on eBay as that is essentially a single fixed channel receiver and you might not hear much. The key here Jack is to start small and take some time collecting info on the Michigan Mighty Mite and Direct Conversion Receivers. You might try to find a copy of Solid State Design for the Radio Amateur as that is a super publication that has many projects and a great stepping stone on the technical side. You might also consider joining the GQRP Club as that is a great source for simple  projects that are usable rigs. Connect with the Membership Secretary – Daphne – she will fix you right up!

 

Chew on what I have sent you and then contact me with any further questions.

 

There is nothing finer than to be able to tell the station at the other end “the rig here is all homebrew!”  Thanks again for your email. You already have many of the things you will need to get launched. Another good starting point is to learn how to use that scope –that is worth its weight in Gold!

 

73’s

Pete N6QW

 I collected the bits and pieces for my Michigan Mighty Mite the day following his email. The only thing missing: a 80M or 40M crystal. Bill offered me some, but he was layed up for a few days. Well, I finally connected with Bill yesterday. Stopped by his shack. Yup, in person. No masks. Very cool. Showed me his MMM and the JOO (Joy of Oscillation). 

I quickly returned home assembled my MMM and, sure enough, got a carrier wave on 3.579:

So, here's my "way forward" for you Govies and former military:

1. Capture this MMM into a semi-permanent design: ie, perf board.
2. Measure performance. What does the carrier wave look like on a scope? Is it a good sine wave? Are there distortions at multiple frequencies? I bet there are! How would I remedy that?
3. Build a low-pass filter to choke out the IMDs for frequencies above 3.579 MHz. How does the carrier now look?
4. Can I amplify the signal? Maybe add an amplifier stage or two. Transistor? LM386?
5. Next, let's look at receivers. Pete & Bill recommend that I build a Direct Conversion receiver. I know Peter Parker (VK3YE) has a simplified version. Can I use these two in tandem with a transmit/receive switch?

That's good for now. I'd like to see how I can use a microcontroller for a better VFO, but I'd like to understand a superhet receiver architecture first. So much to learn.