Thursday, December 4, 2014

A helpful chart for determining resonance of RF Chokes

Hi. I would like to share with you a reference that I have found helpful to keep near the bench. This is a chart for determining the range of resonant frequencies that can be expected for a given inductance value. I keep a copy of it stored with my other favorite RF design tools & software shortcuts. I recommend printing off a copy to keep near your workbench or tack to the wall.

The chart is from a book called "Solid State Radio Engineering", not to be confused with the infamous "Solid State Engineering for the Radio Amateur" by the two greats W7ZOI & W1FB. Rather the originating book was written by Krauss, Bostian & Raab.

"Because of distributed capacitance between turns, every RF coil behaves like a parallel LC circuit and exhibits a self-resonance frequency above which its impedance is capacitive. Since RF chokes are used to provide high impedances, it is important that the operating frequency be less than the resonance frequency. They are made in a variety of forms on phenolic, iron, and ferrite cores, and their resonance frequencies and Q values vary widely."

Click to Enlarge
Click on image for full size.

I hope that this chart is helpful to you.  I'm constantly working on my method of circuit design & construction, often discovering a new tool or reference that helps me achieve more complicated tasks or calculations quicker or more efficiently. I look forward to sharing these resources and other tips and tricks with you here on the Freestate QRP blog. 

Do you have any handy tips for determining values of critical circuit components? What type of RF Chokes do you use and for what applications? . The combination of ferrite beads Do you 'Roll Your Own" or do you prefer the small molded or encapsulated ones? Please share your thoughts with us! 

Would you like to see more resources like this chart? Would you rather see posts on free &/or open source RF design tools? Feel free to email freestateqrp at gmail and let us know your opinions. Alternatively, share your feedback as a comment to this post.

Thanks and 72/73.

Monday, November 24, 2014

Breaking the speed limits of classic TTL based homebrew RF designs*

Breaking the speed limits of classic TTL based homebrew RF designs*
*with Potato Chips!

Hello. This post shares an idea about using highspeed TTL chips in classic TTL circuits.

When I first heard about Potato Semi AKA Potato Chip, a semiconductor company, I thought that maybe it was just a joke. If you read some of the wording on their webpage, there are a lot of "potato chip" jokes & puns, playing on their brand name, hidden throughout the text. However, once I saw that not only was this a real company but that they are offering high speed (1GHz+) versions of classic TTL chips, I immediately got excited. There has been a great number of TTL based homebrew projects published over the years. These circuits have often been restricted to a few bands due to the maximum frequency limits of the TTL families used in these projects. With the new availability of these highspeed chips, perhaps we can "break the speed limit" of these old projects and expand them out into new bands, higher up into VHF or even UHF. Certainly there are many other design considerations that will come in to play when building for higher frequency VHF/UHF circuits. But perhaps it would be worth starting by experimenting with low VHF frequencies just above the frequency limits of previous designs.

Potato Semi currently has 24 highspeed TTL chips listed. They call these chips their 'G Series GHz TTL/CMOS logic ICs'. Thats a good starting point for determining which classic TTL homebrew design may be viable for "scaling up". The chips are surface mount but I have a good quantity of SMD breakout boards. If you decide you would like to experiment with these chips for homebrew but have difficulty working with SMD components. Send an email & I will work out a way to post you a couple SMD breakout boards for the package type you will be working with. In exchange, it would be most appreciated if you could share the results of your experimentation (even if just a sentence about a catastrophic failure).

This is just an idea. For all I know, there will be some significant issue with using these chips for homebrew RF design at frequencies higher than the classic TTL families where capable of. But I wanted to at least get the idea out there to others that have a drive to experiment too.

Is there a serious flaw in this idea that I haven't thought of yet? It will certainly require experimentation. I need to be able to acquire a few chips first, that cost money so that will take a little time to happen. Maybe you have already tried this. If so please share your thoughts, success, failures. Maybe you know that this is doomed from the start, if so, please speak up so we can discuss this. I am just passionate amateur homebrewer so there is a great deal that I do not know and will never understand but I love to learn, so please feel welcome to share your wisdom.

The following is from their website, (underline & bold added by me - also "low cost" = $3.00 per chip via their ebay store)

"GHz CMOS Output
CMOS technology has been widely used for more than 50 years. It delivers low cost with high yield; however due to the unbalanced CMOS structure, it will generate high noise into power and ground. In the past 50 years of IC history our GHz CMOS output driver is the only technology that will reduce your chip internal ground and power noise without sacrificing your output performance. Our low noise technology allows the output frequency to be 7 to 10 times faster than anyone else in the world. In addition, this low noise technology allows any ICs with our output drivers to deliver accuracy without errors. The example below shows the output signal from our standard logic 74G32. The VCC is 3V. The output frequency from the measurement is 2 GHz with probe load. The maximum frequency will be more than 2 GHz. VPP is 2.075V, Vhigh is 2.175V and Vlow is 100 mV."

This is pretty exciting for me, as I haven't worked with TTL/CMOS that are capable of such high speed. I can't wait to start experimenting! Just gotta save up my pennies to get some of these yummy potato chips. Please note that I am in no way associated with Potato Semi. I'm just a curious homebrewer.

73, stay fluxy & keep your iron hot!

Thursday, November 20, 2014

The Transistor Islands

Update: See my post with details on how to make your own island pad cutting device.

Hello. Yesterday I found myself needing to build a simple Colpitts oscillator, when I discovered a technique for making 'transistor islands', for lack of a better term. I've tried prototyping using different methods but predominately built using 'ugly style' with dead bugging. I didn't like gluing pads or using high value resistor stand offs though. Eventually I developed the desire/need for more rigid mounting of components so I opted to find a method akin to making islands. Not wanting (or being able to) spend any money on fancy island pad cutting bits, I made some of my own tools to do the job.

I had these wooden handled tools that I must have picked up a decade ago and I'm not even certain what they are used for, but I believe they can be purchased from a hobby store. I used my dremel to reshape the blades of the tools and I use these to make islands. This method was developed based on others I've seen that modify a drill bit to achieve a similar result. The tool is then used to form isolated pads, or "islands", on copper clad board and your components are mounted on these pads. The tool is held in one hand, one point is pressed down and the other point is rotated around in a circuit, cutting into the copper and forming an isolated island.

All of my "island cutters" created pads that where a little larger than what I wanted for this project, so I found that by using a sharp box cutter/utility knife blade (seen wrapped in tape for an ease of use) and cutting sections in the pad, made for a perfect little "Transistor Island". This may seem like an obvious thing to do, but if it wasn't for the many pictures of different circuit building styles online, I wouldn't have figured out how to do it myself. So I share these with you.

Always wear safety glasses and a respirator mask when cutting into copper clad material. The resultant powder can be very dangerous.

The "island cutter" and box cutter used to make the "Transistor Island"
The pads are tinned with solder.

 The transistor is mounted, observing the pinout, continuity must be checked throughout the entire build process to prevent any shorts.

The completed Colpitts oscillator, with crystal socket. The 100ohm resistor with flying lead is for power and the disc ceramic the output.

The final circuit with crystal mounted. 

I should note that this method is time consuming and doesn't lend itself to easy modifications, so it is best for proven designs, rather than experimentation (which ugly style is better suited for). This is a bit more crowded than I would generally like my circuits to be, but this was also the first time I was experimenting with this idea. 

Thank you for taking time to read this. I build ugly circuits and I am proud of that. I would rather build ugly circuits than to not melt solder at all.  What methods do you use? Are you a Manhattan fan? How about veroboard / stripboard? Or do your builds look like those found on the late Jim William's desk?

The workdesk of the late great Jim Williams

Thanks again & 73 from FreestateQRP.

Tuesday, November 18, 2014

Stable Vackar oscillator

Greetings everyone,

I love playing around with different oscillator designs. From the SuperVXO to trusty Hartley, both crystal and LC oscillators are fascinating to build and study. Some designs stand out as working better than others, but it often depends on the application. One oscillator design that stands out to me is the Vackar and I would like to share a simple but stable version of it with you.

AmQRP produces an excellent magazine called Homebrewer. You will find various articles & excerpts from homebrewer as PDFs at various corners of the web. The Handyman's Guide to homebrew construction has been popularly shared amongst the online community.

The circuit I am going to share with you today comes from an article from issue number 7. The article is titled Better Crystal Set and was written by Phil deCaire, WB7AEI. Because I have not asked for permission to share the original schematic image from the article, I have redrawn the schematic using ExpressSCH. I should note that it is issues of copyright that will likely pose a large obstacle in a timely sharing of my favorite designs, as I will have to redraw every schematic that I wish to share. I am open to suggestions and/or influence regarding this matter.

I was impressed with the frequency range, stability and simplicity of this design. We all know that creating a stable VFO* can be a very difficult task. Often times we opt for the rock for this very reason. But even ceramic resonator based oscillators or SuperVXO with a great amount of "pull" can't come close to the range of this oscillator. I have not used this as a VFO/LO but I've used it as a BFO & as a general piece of test gear (sig gen) on the bench with good results.

* click Stable VFO  for link to hanssummers' incredible Huff & Puff!

Originally by WB7AEI from AmQRP Homebrewer #7
7-14 MHz Vackar Oscillator.
Click to enlarge

I would like to hear from anyone else who has used the Vackar design, whether a simple one like this or a more complex version (like G3PDM's Vackar VFO from ARRL HB 2004 - p14.18 Fig 14.15). How does the vackar fail in comparison to other oscillator designs and in what applications does it succeed? Want to see pictures of my build (heads up, I build ugly circuits)? Let me know your thoughts.

I could also get some pictures of the output of this circuit, as well as different results from varying the L element of the circuit. For L, an air-wound coil can be used, but a powdered iron toroid may produce better results. If you would like to see a more in depth look at this circuit, please let me know and I will spend some time making the results of experimentation available here. Otherwise, I will continue to move forward with more blog posts on other topics.

Thank you for taking time to read this. This is the first time I've ever attempted to share homebrew technical info like this. I appreciate any kind feedback and even criticisms (I am human, so please be gentle).

If you are reading this than you are part of the community and your voice is absolutely welcome here, so feel free to share your thoughts on the Vackar or other oscillator designs.

Keep your iron hot, stay fluxy and 73!

Saturday, November 15, 2014

Welcome to Freestate QRP

Freestate QRP is a new group for Kansas radio amateurs and others who have an interest in QRP (low power communication) and homebrewing (homemade) radio circuits. I am the first member, KE0BFF, and I live in Lawrence, KS.

According to FCC Part 97.5 (2) : A club station license grant.

A club station license grant may be held only by the person who is the license trustee designated by an
officer of the club. The trustee must be a person who holds an operator/primary station license grant.
The club must be composed of at least four persons and must have a name, a document of organization,
management, and a primary purpose devoted to amateur service activities consistent with this part.

If you are a licensed amateur radio operator living in Kansas and would like to become a part of Freestate QRP, please contact me by addressing an email to my call sign at qsl dot net. With the ability to eventually become an FCC licensed club, there are plenty of opportunities for you to contribute and participate.

If you are not a licensed amateur radio operator, but have an interest in building circuits or would like to learn more about homebrew RF and QRP. I invite you to email me as well and follow this group.

I imagine Freestate QRP as being a way for us to come together online, on the air and in person and learn from each other. I hope that we can inspire each other by group projects and teaching each other about different modes of operation.

Whether you are are an expert or a beginner, you are welcome in Freestate QRP. Let's learn to communicate using CW (morse code). Even the technician class licensees (which I am) have CW privileges in the HF bands. How about SSTV, PSK31, RTTY & even hellschreiber?

Do you use a boat anchor or an SDR? Are you a new ham like me or do you consider yourself an elmer? All are welcome here.

Please get in touch with me via email. My call sign (see first paragraph) at qsl dot net. Let's get together on the air and get this group growing.

In the meantime I will be adding content to this blog to get people excited about this group.

No matter what your age, status, gender, political or religious beliefs, or any other issue that may make you feel unwelcome somewhere, they do not matter here. It's all about radio!

73 (or 72 for those who need a bit less),