Tag Archives: QRP

First IOTA (Islands), then SOTA (Summits), now BOTA

First IOTA (Islands), then SOTA (Summits), now BOTA (Bumps). From the blog of Steve, G0GYA … reposted by Layne AE1N

Today was 2018 ”Bumps on the Air” day for me. Because we don’t have any summits in Norfolk I have to make do with tiny hills, or bumps!

Two years ago Jim G3YLA and I climbed up Beeston Bump (63m) and did some amateur radio operating. This year I wanted to beat that so drove to Norfolk’s mightiest peak – Beacon Hill near West Runton at 100m. Ta dah!

Actually, this wasn’t a very exciting spot as there are just two rotting benches, a flag pole and trees all around.

Nevertheless, I set up my end fed half weave vertical on a 10m fishing pole and connected up my Yaesu FT817. There wasn’t too much about but I worked John F5VKU (also G8MM) near Cannes with 5W SSB. He said he was struggling to hear me.

My 20m QCX radio – click to enlarge any image.

After playing with SSB for a bit and failing to break some pile ups I connected up my 20m QCX radio and tried some CW. I was really surprised as Karl IV3RJH came back to me, 559/549 both ways. I was running about 2W, he was running 3W.

I do have to fix the sidetone on the QCX as calling CQ sounds more like “thump-de-thump-thump-thump-thump-de-thump”. I have the new capacitors, but am waiting for some new BS170 transistors so I can hopefully up the power level to more like 4W too.

But the QCX is an amazing radio for the money and hey, I built it myself, complete with the case and custom label, so any QSO makes me smile.

Another 20m SSB session with the FT817 and I bagged Jack OH3GZ and Juha OH6QAZ.

At this point I packed away and after lunch headed for Beeston Bump on the coast near Sheringham. I’ve written about this before as it has a fantastic view over the North Sea.

Anyway, I put up the EFHW vertical for 20m and set to with 5W CW from my Elecraft K1. This raised Gert OH/DL7UG and Dima RW4C. I then bagged Fabi IK5IiS near Florence.

Also heard were stations in Cypus and Canada, but the Cyprus station on SSB couldn’t hear me and the Canadian seemed to be sending his life story in CW to another station and I got fed up waiting to call him!

I also had a play with my 3W MTR3, but didn’t work anyone as I could see rain clouds coming and decided to pack up.

So not a bad day’s radio. The Elecraft K1 and Yaesu FT-817 worked flawlessly. I think I was getting some RF into the keyer on the QCX as I had trouble sending “/P” – the “/” turned into a right mess sometimes, although I had no trouble sending it on the K1 with the same Palm Paddle.

The moral is that life is NOT too short for QRP!

 

Biking and Playing New England QSO Party

“Hello police! There’s a wierd dude on the side of the road with a bike facing across the field. Keeps writing stuff down and we heard odd beeping noises … better check him out!” —Layne AE1N

“On Sunday, May 6th, 2018 I rode my bicycle to a construction site with a good location for working portable. I set up my SOTABEAMS dipole and used my YouKits HB1B Mk III to make some contacts. The New England QSO Party event was being held that weekend and I worked 6 stations in a fairly short time. It seemed like the sidetone of my HB1B devolved into lots of clicks and very little tone after a while. Not sure why but it was annoying.”

 

A Block Diagram for the LNR Precision MTR3b

When I was a young child, there was nothing more dangerous in the house than me and a screwdriver. I took everything apart. Nothing was safe. I wanted—no needed—to see the insides of things, and see how they worked. At some point, learning how to put things back together was the only thing that kept me from a seriously sore backside. Still, every bit of it was worth it, and I have retained that kind of curiosity throughout my life and my career. 

Things are a little easier today. You can understand a lot from just looking at the drawings for a device. One of the things I enjoy doing is looking over radio schematics and trying to understand how they work, and the choices that the designers made. In this article, I’d like to do that for the three-band Mountain Toper MTR3b, a radio designed by Steve Weber (KD1JV) and sold by LNR Precision.

The MTR3b is a CW-only, 3-band (20/30/40) radio that can fit in the palm of your hand. The photograph of the radio with an accompanying 9-volt battery gives you some idea of its size, though you don’t truly grasp the compactness of the unit until you hold it in your hand. The 9-volt battery is not just a prop for the photograph. The radio can be powered by a single such battery, though it works better with something a little larger. I use a compact 11.1-volt LiPO battery packs made popular by drone users.

I’m not going to provide a detailed review of the user interface (just 3 slide switches, four buttons, and a single 7-segment LED), or go through its on-air performance. There have been several excellent reviews for this radio in QST and other places. Instead, I’d like to take it apart for you. Well, not exactly disassemble it as much as analyze the schematic and see how Steve Weber made it work.

I was lucky enough to have a fellow named Mr. Davis for my high school physics instructor. He said many wise things (that I only understood long after high school, alas), but one that stuck immediately was his adage, “If you can’t draw the picture, you don’t understand the problem.” How very true! So, I often made models and block diagrams of things to better understand them. These models don’t need to be exact. In the words of George Box, “All models are wrong, but some are useful.” A block diagram of the insides of a transceiver can be useful. Here’s the diagram for the MTR3b I sketched on my iPad Pro tablet a few evenings ago.

Let’s walk through it. The antenna is on the far left. The antenna connects to the radio and is presented to a low-pass filter (LPF). As it turns out, each band requires its own special LPF so there are slide switches on the front of the radio to switch-in the correct filter. Switch position 1 is for 20m, switch position 2 is for 30m, and switch position 3 is for 40m. The way the radio is designed, as we will see, it is important that all three switches be in the same relative position for the radio to operate properly. 

The next thing in line as we walk towards the receiver is a transmit-receive (T/R) switch. When we transmit, the signal path is cut off from the receiver and the transmitted signal only goes to the antenna. When we are receiving, the signal path is routed to the receiver, pictured along the top of the diagram.

After we pass the T/R we have a band-pass filter (BPF), also selected by one of the slide switches, that rejects out-of-band signals. This is the lead-in to the first mixer that generates the intermediate frequency.

We should take a quick detour for a moment and review what a “mixer” does. A mixer is an electronic device that takes two signals in and yields four signals out. It sounds complicated, but it really isn’t. Say we have two signals of frequency A and B. The mixer will output those same frequencies A and B (not very interesting), and two other signals: A-B and A+B. These signals are interesting. 

Superheterodyne receivers like this one mix the received signal with one from the radio (tied to the main tuning system) to produce an intermediate frequency that can then be further processed. By turning the original signal received from the antenna into this intermediate frequency, we can have a system common to all three bands 20m/30m/40m in the rest of the receiver. This common system works because it only has to deal with signals at this selected intermediate frequency. The intermediate frequency selected by Steve Weber for this design is about 4.1 MHz.

After we mix the signal with the first mixer (illustrated as a circle with an X in it), we pass the resulting signals through a crystal filter that allows only the 4.1 MHz-related frequencies through it. This is the A-B output from the mixer. The other products are discarded. Once through the crystal filter, we now have a nice signal from our selected frequency, but it is in the 4.1 MHz range. We need a subsequent step to bring it down to the audio frequency range.

The product detector that produces the audio frequency range signal from the 4.1 MHz intermediate frequency is obtained by passing the signal through a second mixer. When we’re through here, we have something our ears can hear. All that is left is to bring that audio signal through a few amplification stages, and send it to the headphones. This radio is so simple that it doesn’t even have a volume control! 

Just before the headphones is a multiplexor that allows audio to be selected from either the receiver (as we’ve just done above), or from the sidetone generated when we send Morse code. The CPU generates the sidetone signal and controls the multiplexor. This is the whole receiver.

The transmitter is even more simple. The Texas Instruments extremely-low-power CPU watches the paddles, slide switches, and push buttons, and controls the 7-segment LED display. When dot or dash paddles are pressed, it signals to the DDS (Direct Digital Synthesis) frequency generator to output a signal. (The DDS is also used to select the receive frequency.) The output signal is sent through a few amplification stages, the T/R switch is changed to transmit, and the amplified signal is sent to the antenna.

I was able to get all this just by perusing the schematic included at the rear of the MTR3b manual. You can download the manual for free from the LNR precision website and follow along from the block diagram I’ve provided.

Every time I do this for a radio I feel like I’ve learned something new. It is also gratifying to use a radio that you understand, and know how it works under the hood. 

http://www.lnrprecision.com

Scott, NE1RD

Project Night 2018

Every January Meeting we hold Project Night, where members bring in and share recent homebrew projects that they have built. This year’s Project Night was full of interesting projects built by our members.

Member Projects
Scott NE1RD Kits
Scott NE1RD Kits

Our Programs Chairperson, Scott, NE1RD led it off by showing us some kits he had built, including the K1EL PaddleStick Keyer that we will be building for the February Tech Night.

Bob KB1TEK - QRP Kits
Bob KB1TEK – QRP Kits

Bob, KB1TEK brought some QRP kits that he had built.

Dave K1DHP - VLF Detector
Dave K1DHP – VLF Detector

Dave, K1DHP showed us the VLF Detector that he built.

Hamilton, K1HMS – Antenna Switches

Hamilton, K1HMS brought Antenna Switches that he had built.

Dave K1DLM - Heakthkit
Dave K1DLM – Heakthkit

Dave, K1DLM showed us a Heathkit that he plans to build.

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Dennis, K1LGQ had another explosive presentation when he showed us a KX2 stand that he built.

Dennis shows plans for his KX2 Stand
Dennis hows plans for his KX2 Stand

 

Fred AB1OC - Low-Band Match
Fred AB1OC – Low-Band Match

Fred, AB1OC brought an 80m band matching system that he will install in order to make our 80m delta loop be resonant across the band.  He has programmed our MicroHam system to automatically have the box switch the matching system as we tune through the 80m band.  I’m looking forward to using this to get the last 20 80m contacts for my 5 Band DXCC!

Anita AB1QB - CW Pi
Anita AB1QB – CW Pi

I (AB1QB) demonstrated a Raspberry Pi project that I built over the holidays.  It is called a Morse Code Virtual Radio.  When you hook up a monitor and a straight key to the Raspberry Pi, it will decode what you key in.  This was a big hit with the kids who visited us for ARRL Kids Day.

Mike, AB1YK - Panadapter
Mike, AB1YK – Panadapter

Finally, Mike, AB1YK brought in a number of projects that he has done including a Panadapter and a CW Generator.

Anita AB1QB - CW PiScott NE1RD KitsMike AB1YK - PanadapterMike AB1YK - CW GeneratorHamilton K1HMS - Ant Switches 2Hamilton K1HMS - Ant Switches 1Fred AB1OC - Low-Band MatchFred Ab1OC - Low-Band Match 1Dennis K1LGQ - KX2 Stand 2Dennis K1LGQ - KX2 Stand 1Dave K1DLM - Heakthkit 2Dave K1DLM - Heakthkit 1Dave K1DHP - VLF DetectorBob KB1TEK - QRP Kits 2Bob KB1TEK - QRP Kits 1

Overall it was great to see all of the projects that our members have been working on. The gallery above contains more pictures from Project Night.

Anita, AB1QB