This web page imbues the spirit of experimental electronics — sharing ideas and potentially future site content. I edit the essays continually. The schematics on this page may contain errors. Mouse over images to read a brief description.
I list new, permanent content on the QRP - Log page.
April 8 2012 — Almost Done
I break from the bench from April 26 - Oct 4 each year to recoup and go outdoors.
Over the late Spring and Summer, I hope to add a few experiments from Fall - Winter, however, only if I get time away from our garden, taking photos and hiking. The web site tasks — design, build, photograph, hand-draw schematics, write and re-write content, maintain a server (4 computers in a rack) and answer emails — all consume lots of time and energy.
I plan to make some serious frequency-domain test equipment next Fall and just ordered the parts and sought advice; lots of fun ahead.
The spirit of Ham radio imbues making your own gear when possible. What will you build next?
Have a great Summer!
Above — A simple VHF oscillator for testing 1-off experiments. Click for another photo. Simpler than building a dedicated VHF signal generator, a 1 time VFO might work for builders who only occasionally dabble into VHF.
Above — The schematic for a simple bench VFO. Operate it as shown, or better yet, drive a 50 Ω amp + attenuator pad to peak filters, or measure the gain or return loss of any fixed frequency VHF amplifiers you're working on. Click for a 'scope shot with the VFO set to 144.1 MHz by carefully tweaking the air variable trimmer capacitor. Varactor tuning might boost its versatility?
Above — A version of a 200 MHz oscillator designed by Bob, K3NHI. Bob varied the oscillator amplitude with an ALC driven NPN transistor controlling the stage current instead of a 100 Ω decoupling resistor. Run at 210 MHz, this circuit provides a LO for a 0 - 100 MHz sweeper project Bob posted on the EMRFD Yahoo group . Click for a 'scope capture.
The low-pass filter and pad ensure a clean signal with a decent return loss. For many, 200 MHz represents a maximum scope bandwidth, so we can't view the 2nd harmonic up at 400 MHz.
The above experiments marked the first time I built a transformer from air wound inductors. I made the 1 turn link slightly larger in diameter and wrapped it around the middle of the 4 turn primary coil. You can move the 1 turn link around to alter coupling — very cool.
April 1, 2012 — Good Vibrations; VHF Signal Generators
Above — A negative resistance, 1-port oscillator shown in EMRFD as Figures 4.13a and 4.21. Using the basic multivibrator circuit from the MC1648 emitter-coupled logic (ECL) wide range VCO. This easy-to-build circuit just wants to oscillate. I built a couple of versions, including 1 with a bandwidth of 35 MHz using a single L and 2 SMT varactors (BBY40 in SOT-23).
The MPSH81 exhibits an fT of ~600 MHz and I stock SMT and hole-through leaded versions purchased on eBay.
The obsolete MC1648 IC seems quite amazing: output ranging from VLF to VHF with just 1 voltage control — a dream part for sweep circuits. ECL died off and unfortunately, the MC1648 exhibits a large noise bandwidth making it undesirable for signal generators depending on what tests you perform.
While okay for a simple, homebrew spectrum analyzer, or
to sweep and align L-C
circuits, the simple oscillator above is unusable as a receiver LO where its
moderate to high phase noise could degrade reciprocal mixing performance,
raise the noise floor and trash sensitivity. This circuit offers 1 option for a simple, wide frequency range VFO or VCO.
Some builders prefer the POS series of VCOs from Mini-Circuits, however,
they aren't cheap.
For frequency control, I turned a 100K pot, however, real-word applications might include coarse and fine control pots driving op-amps with added temperature compensation circuitry. A low-Q inductor + clipping of the AC signal by the "2 diodes" leads to low resonator energy and output ( -22 dBm or so ).
In 1 circuit, I connected the VCO to 2 cascaded 50 Ω feedback amps, a low-pass filter and a pad for a 7 dBm output.
At 50 MHz and above output waveform distortion looked suprisingly low, however, as you drop the frequency toward 39 MHz, distortion emerges. Click for a FFT at 121 MHz where I saw a pristine sine wave; Click for a 'scope shot at 71.9 MHz (no attenuator pad); and Click for a 'scope capture at 46.2 MHz. You'll need a low-pass filter for wide frequency applications.
The L is non-critical. We normally wind on a number 6 material toroid for temperature stability. The 1 turn link = a short piece of hook-up wire grounded one 1 end and passing through the toroid center to the attenuator pad.
VHF Signal Generator Recommendations
Having started at VHF in November 2011, my knowledge suffers, however, a search for accessible, affordable, good quality VHF signal generators disheartened me. Ten year old or newer signal generators covering the VHF band work up to several GHz and cost a small fortune.
Lamenting old timers often recommend the vaccum tube HP-608 series that covered ~10-480 MHz. These heavy, glowing beasts sometimes come up in estate sales or on eBay for $200-400.
Then, too, the HP8640 series seems attractive, however, they are full of decaying parts. Ken Kuhn and others restore old HP gear as a hobby and this direction certainly gives us a valid option.
I've investigated 1 or 2 new, low-cost signal generators that work into VHF, but they failed to excite me; especially after I downloaded the schematics and sat in disbelief over their poor design.
Some minimum commercial signal requirements might include stable, linear tuning, a metal chassis, 50 Ω output with a return loss greater than 20 dB and low harmonic distortion at all frequencies. Like the rest of our lives, our budget usually determines what we buy.
I decided to build my own VHF signal generators and document them on this web site. I've learned that home building signal generators between 50 and 200 MHz requires skill and care, but can be done.
What about digital clocks?
At VHF, DDS spurs get extreme as you get closer to the maximum clock frequency .
The Si570 looks intriguing, however, still requires PLL components, I haven't read any lab quality evaluations of the Si570 as part of a VHF signal generator and if you know better, please email me.
A Basic RF Workbench
Since January 2012, a handful of readers asked what I consider a good basic RF work bench. Again, I'm just an amateur hobbyist, so my opinion might show my ignorance.
A
stand-alone 50 MHz oscilloscope with at least one 10X probe. More
bandwidth if you plan to work above 50 MHz- If no
oscillocope, an AD8307-based power meter The modern version of the diode RF
probe.
- 3-4 50 Ω
coaxial cables with BNC connectors; a 50 Ω scope feed-through terminator, 1-2 50 Ω
BNC port terminators, a though-connector and some BNC connectors to
solder onto temporary
circuit boards or mount in a chassis.
- A homebrew return loss bridge.
- 3, 6, 10
and 20 dB BNC connector equipped attenuator pads, or a step attenuator.
- Signal
generator(s) that cover most of HF; +/- VHF signal generators as described
just above this section.
- AADE L/C
Meter IIB. Click
- 12 volt
regulated power supply good for at least 1 amp.
- Digital multimeter. I use 2 and keep 1 set up for current measurement only.
- Frequency
counter: homebrew or commercial. I ran a 40 year old, ovenized,
accurate HP counter until 2012.
With these devices, as possible, you can work in a modular, 50 Ω environment and measure gain or loss in dB, return loss in dB and absolute power in dBm. Starting small and expanding your bench around 50 Ω input and output impedance devices will provide a lifetime of challenge and excitement in RF design.
Later, the big toys can follow: spectrum analyzers, VNAs, commercial signal generators and other lab quality stuff.
Equipping an RF bench presents quite a financial burden. I started small and slowly added pieces over time. Many pieces such as my L/C Meter IIB were gifts for holidays or my birthday. Other pieces were old, inexpensive equipment that I restored and calibrated.
Above — RF tools of the trade. As scratch homebrew builders, gear like BNC, SMA and through-connectors, 50 Ω terminators and inline attenuators lie scattered on our benches.
In another blog post, I'll discuss building up your parts collection — another costly adventure.
March 19, 2012 — 50 MHz VCO Update
I've moved all the 50 MHz VCO material to the VHF to the Max! web page
March 11, 2012 — Homebrew Radio Gaining Traction Worldwide?
Some QRP home builders occasionally update me with their progress and quite frankly, I love it — Homebrew radio = a really creative hobby and viewing their work drives my own creative process. What are your thoughts?
With respect to bread boarding, some builders just won't do Classic Ugly Construction — that's okay, and I think the reasons include aversion to ugliness, pride, lore, love of designing boards and fondness for super stable component stand-offs. Who really knows? I build in Classic Ugly style because it's fast.
Above — Larry, N0SA sent this photo of a CNC-routed copper board. You may know Larry from his beautifully machined paddles. Larry provides yet another wonderful variant of Ugy Construction. Click to see this board populated with some parts — is this cool or what? . Larry built a Dave Benson design superhet-transceiver (I've scratch built 3 Dave Benson, NN1G radios and he's 1 of my all-time favorite designers). Click , click, or click for more examples of Larry's work that includes homebrew cabinets and metal knob detailing.
Above — Anthony's VFO. Anthony studies electronics in a South American University. He checks in about once per month and builds crazy-amazing stuff. Like me, he builds in the Classic Ugly style and
Above — I'm studying amplifier design and generating QRP / SWL HomeBuilder web content + an article for a Ham journal. I vacate my bench in late Spring and all Summer to spend time outside + watch football, so I must generate enough web site content each Fall and Winter to last the whole year.
Above — A U310 JFET. Rare and expensive; but the greatest part ever for low-noise common gate amplifiers. I'll be adding this part to a 6M band receiver front-end and hopefully posting it this Summer. As an amateur builder, I love handling cool parts like the U310.
Keep up the good work y'all.
March 2, 2012 — 19 days until Spring
The best stuff I've seen lately comes from others. Nothing makes me happier than to see people design and build their own gear...
Popcorn QRP Homebrew
I'm amazed at the number of builders beginning or rediscovering homebrew radio electronics. Some email me photos + offer vivid discriptions of their design and breadboarding experiences. "Joie de vivre" abounds. Consider the handywork of Boris, YU2UD from Serbia who designed his popcorn transceiver + circuit boards and then assembled this gorgeous rig. Click or click for photos of his popcorn superhet receiver and transmitter with break-in circuitry — all cleverly built into a Kenwood 520 remote VFO chassis. Pure inspiration!
MDSR
This Winter, Alex, VE7DXW emailed to share the soundcard software (MDSR
Modulation – Demodulation Software Radio) project he and Guy, ON6MU
developed and continue to hone.
Their innovative approach allows
hobbyists to use favorite old analog transceivers, or
more modern rigs like the FT-817, IC-703 and transform
them into SDR filtered/demodulated/modulated receivers and transmitters. All of their efforts are
non-commercial and the MDSR team includes 543 members on a Yahoo user group. World-wide contributers
advance this exciting project and their efforts are published
annually in the TAPR magazine.
Check out the
MDSR website hosted by
Guy, ON6MU.
MDSR Software
The MDSR software
modulates and demodulates 12 KHz AF signals. All you minimally need to run this
app is a Windows XP computer + a decent sound card (For example, a 24-Bit Audigy
card).
MDSR Hardware
To drive the MDSR computer software via a sound card, incoming and
outgoing signals are converted from your rig's 455 KHz to 12 KHz (or back) with a
Bi-directional Low Internal Frequency (Bi-LIF) converter.
For SWL, or
receiver-only applications, you may design and/or build your own 455 KHz
I.F. to 12
KHz converter, or opt to purchase a receive-only kit employing an NE602
Gilbert cell mixer and with a seperate local oscillator from the MDSR web
site.
Please consult the extensive MDSR web site. Big
thanks to Alex and Guy for their great work!
February 15 , 2012 — VHF to the Max! Update
Above — I moved all the MAX2606 experiments to a new, permanent web page called VHF to the Max!
Tunable Hall Network
Professor Kuhn recently published a paper discussing a Tunable Hall Network for Electronic Design. I 'll wait until the print version becomes available before experimenting with it, although some may prefer the web version.
His tunable Hall network should fit many applications including duty as the filter in an audio distortion analyzer, since you get both the band-pass + notch filers which improves performance over just the notch alone.
January 22, 2012 — Feedback Amps at 50 MHz
Above — An experimental hybrid-cascode feedback amp for 50 MHz. Despite much bench tweaking and trying multiple output transformers, a strong output return loss eluded me (only 10 dB). Shunt feedback obviates the high reverse isolation we normally get with a hycas amp; a good fact to know. The poor output return loss and low reverse isolation puts this circuit into the "failure pile". I'm comforted by the fact that it's not an epic fail !
I've found RF design at 50 MHz on up much more difficult than at HF — I can't imagine what the microwave experimenters go through when bench designing their circuits.
Above — A prototype board laden with NEC's NE46134. After floundering around with the hycas amplifier above, I returned to the familiar Beaverton Special topology — designing around the NE46134. Although, I'll still use the 2N5109/2N3866 pair for bench surfing, this SOT-89 part really shines and now = my go-to medium power, microwave fT BJT. Watch for instability!
Above — The 50 MHz feedback amp schematic. I tweaked every resistor + the current to find the overall best gain, return loss and signal handling — my hand calculations and bench experiments matched. More current improves the maximal signal amplitude the amp can handle + boosts gain, however, lowers the output S11. Normally a 3 to 6 dB pad follows a Beaverton Special feedback amplifier to preserve the input S11 and this happliy boosts the output S11 too.
This amp will likely serve as the final stage in my future 50 MHz VFO.
Above — The feedback amp breadboard. A commercial 10 dB attenuator threaded onto my 50.0 MHz oscillator helped drive the amp with a well matched signal generator. The whole SOT-89 prototype board serves as a heat sink — even at 35 mA emitter current, it was only warm to touch (27.3 degrees C).
January 1, 2012 — Happy New Year!
Books
Above — New books added to the QRP / SWL HomeBuilder library for 2012.
NDB
This Fall, I exchanged emails with another NDB enthusiast concerning low-pass filtering for Non Directional Beacons. Click for her web article NDB A Low Pass RF Filter in an Altoids Box Design and Construction of a Low Pass Filter for the Low Frequency RF Spectrum by Dr. Carol F. Milazzo, KP4MD. Also consider viewing her on-line power point presentation and awesome web site.
I recommend using # 61 ferrite toroid mix for NDB low-pass filters — higher Q and less losses than # 43 material.
December 17, 2011 — VHF - Butler Oscillator Experiments
Above — I moved the Butler Oscillator Experiments to a new web page called VHF - Butler Oscillator. Access through the top level 2010- 2011 menu. This concludes the new web page content for 2011.
Tilman, SM0JZT exhalts passion and curosity for circuits, that I relate to. Swedish builders have long contributed to amateur electronics design. Another example = Harry,SM0VPO who operates 1 of the best and most popular Ham construction sites in the world.
Above — The web site of Tilman, SM0JZT as it looks with Google Translate. Link
December 4, 2011 — Preparing for VHF Experiments in 2012
Equipping the QRP work bench for 50 to 175 MHz both challenges and stresses you: What bipolar transistors should I stock? What oscilloscope to purchase? What about signal generators — VFO, VCO, DDS, or perhaps a VXO, or a fixed crystal oscillator mixed with a VFO runniing at low HF? With all of these decisions, it's easy to get overwhelmed.
Consider the raw VFO design above. I built it today and became impressed. I can probably tune it from 47 to 54 MHz with parts on hand. Frequency stability with an air coil is good enough and might be improved with temperature compensation. I even built a version with a T37-6 toroid inductor, but the air coil beat it for temperature stability. I seriously considered making my 50 MHz signal generator with a properly buffered circuit like the 1 above.
Above — A photo of the experimental 50 MHz VFO with only a resistor for a load.
Above — I've been experimenting with air inductors (solenoids). At VHF, inductor lead length becomes relevant and a wire has an inductance of a half to 1 nH per mm of length.Some of the coils I plan to use up at 104 MHz have an L of 300 nH or so, so boy there is lots to learn about winding and using solenoids. Winding on a bolt was suggested by Wes, W7ZOI and gives some degree of reproducibility. A U.S. friend sent a photo of his VHF coil forms — he emphasized the importance of well securing your air coils; the mechanical stability issue again!
I also "paper designed" some bench filters that won't ever be published until they are built and tested. For example, click for the GPLA simulation of a mixed-style, tripled tuned band-pass filter for the 6 Meter Ham band. 3d B bandwidth = just over 2 MHz. The L = 270 nH — kind of shocking to think about. Before making any VHF filters, some signal generators and a return loss bridge need to be built. Lots of work ahead, but I am stoked to transition to and learn about VHF. I'll document my journey into VHF on an upcoming VHF 2012 web page.
I conjecture that 2012 will be the best year ever for scratch homebrew radio builders.
Snapshot of Mary. I shot this photo of Mary with an old point and shoot 35 mm film camera in Moldova. Mary served as my email and server manager off and on until 2010; now she's raising a baby. I've been shooting film all month and just love it.
Currently, Galina Nikolaevna runs QRPHB while I'm on hiatus. Galina models professionally in Russia, Moldova, Ukraine and Belarus. She won't let me post her photo and it's too bad because she's so incredibly beautiful.
I've been mixing signals with the LO and RF over 100 MHz to examine filter design. Click for a 'scope shot of unfiltered RF at the IF port of a SBL-1 mixer. Time to move to a frequency domain instrument — next Fall.
All web site photos taken by me or my family unless stated otherwise. Thanks.
