Tag Archives: QRP

First Homebrew Contact on my Scratch Built BitX 20 SSB Transceiver

About a year ago I decided to build a SSB transceiver for making contacts with other amature radio operators on the HF bands.  I was given good advice from both Bill and Pete from the SolderSmoke Podcast  to start out with a direct conversion receiver then go with the BitX as a fist SSB rig.  I am very happy that they gave me that advice and I would agree that the BitX is not a good first project.

After getting all the proper adjustments made and confirming proper operation with a dummy load it was time to put this rig on the air (I don’t need a case)!   I tried calling CQ using SSB voice but no one came back.  I then decided to add some relays and other modifications to allow digital modes.

On January 15, 2017 at 21:46z I answered a psk31 CQ from Josh K1JOG in Kissimmee, FL.  Little did he know that he would be making history (maybe just for me) in my first home brew QSO.  Below is his eQSL card to me.

Thank you Josh K1JOG for the contact!

If you are interested in scratch building this rig you can follow the photo link  below:

BitX by Ashhar Farhan, VU2ESE

Ashhar Farhan also sells a BitX-40 at http://www.hfsigs.com/

The units he has built in India are almost ready to put on the air.  You build the case / box or just go open board style!  You can’t beat the $59 price for a rig!

Below are some photos of my project:

Mic amp on the left LM386 audio amp on the right

A good place to start is the Audio “end”.  I built mine using perf prototype board.  FYI the 10k ohm resistor on the mic amp needs to be 39k ohm for proper bias.

Balanced Modulator
Balanced Modulator

On the balanced modulator, I used a mystery toroid core because I have a bunch of them and they did not cost much!

10 MHz crystal filter

In this photo you can see some transmit and receive amplifiers and the crystal filter.  I built some test equipment and used a frequency counter to make a matched set of crystals.

Mixer circuit

The mixer circuit is shown here with some coax to the left that is from the VFO.

Original VFO design on the left. Filtered SI5351 clock generator on the right

You can see the benefit of building small modules.  With SMA connectors, I can quickly swap out the VFO “soul” of this rig!  No more drift with the SI5351 chip! I ordered mine from Adafruit. I added a small LC filter to the output to make a nice sine wave.  I am not sure it is needed.

Band Pass Filter by Pete N6QW

Now I had trouble with the original band pass filter.  I’m not sure why but a quick google search on 20m band pass filter and I found a replacement circuit on his website.  When I told Pete about this he sent me a new updated design to try.  My PTT relays are 5v so the small heatsink is for a voltage regulator.  I also included diode protection for the replays.

Irf510 power amplifier

The IRF510 is more of a switch and not designed for linear RF amplification but it is cheap and works great for QRP.  They have different bias requirements from one unit to the next.  That is why you carefully set the bias level with a trim pot.  The large heat sink was part of an old high power LED driver that died.  I used T37-6 toroid cores for the low pass filter on the right. The 2nd relay was needed to prevent the output of the IRF510 feeding back into the original PTT switch and back into a nasty loop.

I am not sure if this rig will ever get a case or future modifications but I do know that I would like to see if I can make more contacts with it.

I would like to end this article with a quote I very much like from a video with Rev. George Dobbs, G3RJV

“Radio construction is rather like a pilgrimage where the journey is often more important than the destination”.

73,

Mike,  AB1YK

A First Homebrewed Transceiver

I recently wrote an article about Nashua ARC’s 2017 Project Night (forgive my shameless self-promotion). In it, I expressed my awe of what our club members can do, and how it has inspired me to attempt my own first build.

The winter really is the best time to do this. And it’s time for me to embark on this journey of fun, learning, and frustration! So I turned to Mike (AB1YK) who knows about such things, since he and I are attempting to organize a future summer weekend Tech Build Event for the club. The Pixie and the DSO138 oscilloscope are the warm-ups for this main-event. One suggestion Mike threw out was a Direct-Conversion Receiver (DCR) as advertised in the January 2015 issue of QRP Quarterly which you can actually download here (and as far as the application to the Tech Build goes, perhaps we only build parts of the DCR given time constraints). This article is entitled Let’s Build Something: Part I by Ben Kuo (KK6FUT) and Pete Juliano (N6QW).

In it, they outline the main building blocks of the build. The nice thing about this build is once one is done, it is amenable to some modular alteration to turn it into a fully working QRP SSB transceiver! (Though I do not know how much wattage at this stage) The other nice thing about this build is all the parts are clearly labeled and Pete provides links at the end of the article for YouTube videos about the build. Maybe it’s just my noob eyes, but I find the videos moderately useful for someone starting from scratch, but I can see the utility for a more experience builder. Additionally, this build utilizes the Manhattan style of building. I find this optimal for someone just starting out because I can easily visualize all the connections between the components and have relatively easy access to make measurements and tests with probes.

Let’s go through parts and I’ll tell you what I know (at a cursory level) and what I don’t

  • 40m bandpass filter: Totally on this one. I’ve never built a filter before but looking forward to doing this. In fact I need to build one for my ADS-B antenna at 1090 MHz, but it doesn’t seem feasible to do from components at that frequency. Any ideas anyone? I’m kind of stumped.

  • RF amplifier: REALLY looking forward to tackling this one, but this won’t be the first thing I do. Makes sense to have for weak signals.

  • Double-balanced mixer: Now I know something has to knock the RF down to an intermediate frequency (IF) and when I see mixer, this is where my brain goes.  The double-balanced bit was foreign to me, but as advertised in the article (‘double balanced’ implies that the original signal and local oscillator frequencies are deliberately nulled out as part of the mixing process and do not appear at the output.)

  • Arduino Based Sample DDS: In order to even produce an IF, we need a local oscillator (LO). This is where the Arduino comes in. The authors argued they looked at a number of options for the LO including a VFO (variable frequency oscillator), varactor tuned oscillator (should know this from my Extra exam — but full disclosure — I can’t help you now), and a DDS (direct digital synthesizer). They felt the simplest option was the DDS (hence the Arduino).

  • Audio amplifier: We want to amplify the audio signal so we can hear it through our 8 Ohm speaker!

So now if you put all the components and modules together, you arrive at something which should look like:

I like this project for a few reasons.

  1. It’s a more interesting build and takes longer than 2 hours.
  2. It will have amateur radio applications in my shack. I do hope to work some pretty cool QRP with this rig (when I turn it into a full-on transceiver).
  3. I will learn A LOT about the electronic components integrated into the rig and be able to have an excuse to buy some test equipment.
  4. I get to work on my soldering skills.
  5. The modular design is attractive so that if I wish to make alterations in the future, it seems I will readily be able to do so without having to tear the entire rig apart.
  6. Understanding, at the end, how all of these parts function together to make my transceiver work. I look forward to sharing whatever knowledge I accrue during this build with future amateur radio hobbyists just breaking in.

I will certainly post articles as my progress commences. Currently, I am in the market to buy components and test equipment and will begin to build probably the simplest module first; currently that seems to be the filter. And I have learned a very valuable lesson from being in the club and participating in its activities that I am applying to this build. Initially do things to set yourself up for the highest probability of success so that you keep your morale, interest, and momentum high. Nothing is worse than diving head-first into the hardest part of a project and losing any and all ambition when things begin to not work (and they will…).

73,

Brian (AB1ZO)

Upcoming Tech Night Suggestions Forum

At our most recent Tech Night meeting on Sept 12, at the end of the meeting, Fred (AB1OC) asked Brian (AB1ZO) to list a few of the upcoming tech night events.

One such event would be to host a kit-building tech night. Plans are in the works to secure Pixie QRP kits (which run in cost from $3-$13) or some variant of this, and assemble the kits during the allocated time. It’s expected that more experienced HAMs can mentor newbies in endeavors such as these.

Secondly, an informal poll was asked of members in attendance regarding the types of topics that would be of general interest. These included:

  • Low-band antenna discussion: Due to the decreasing sunspot activity, “40m is becoming the new 20m”. What options to HAMs have to get on the lower bands, particularly if you are real-estate limited?
  • Receiver vs Transmit antenna discussion — options for both
  • High-frequency terrain analysis (HFTA) in order to better understand propagation effects of one’s signal
  • Making sense of the influence of sunspot activity on amateur radio in general. Some emphasis, for example, could be dedicated to interpreting the sunspot GUI that appears on the website after login and understanding the science of the ionosphere.
  • Working more with test-equipment kits and how to use them. This may include oscilloscopes, spectrum and network analyzers, frequency counters, signal generators, building CW paddles/keyers, and soldering kits.
  • Using RTL-SDR dongles (or again some variant) and using them in small DIY projects that we could potentially complete in the alloted time.

I do want to say a few other things:

  1. Since our club is growing, and many new people are joining, I do want to stress that it is important that sometimes we “recycle” old Tech night topics in an effort to better educate our newer members. In this capacity, I would again hope that veteran members could help train younger ones. For example, I cannot solder to save my life. I would love some training during a surface-mounting tech night (since I couldn’t make the last one) and have someone experience show me the ropes.
  2. Many of you are working on interesting projects at home. No matter how small or large you think it is, I am 100% certain there are a group of people within the club who would like to hear what you have to say. So if you would like to present at Tech Night something you have been working on, please do not hesitate to email me at bsmigs@gmail.com.
  3. I also want to solicit your feedback on this blog as well as my email for any other topics. The more suggestions we have the merrier! It’s important we adequately represent the interests of as many members of the group as we can.

In the coming weeks, I will start to construct a more concrete list of potential Tech Night topics, but help me — help you 🙂 Thanks for reading and see you on-the-air.

Best and 73,
Brian (AB1ZO)