Walter's VFO

Main VFO board under plastic -- buffer board off to the right

There is a lot of tribal knowledge in this short article by Walter KA4KXX.  (The most recent issue of SPRAT has a picture of a SPRAT cover from more than 30 years ago, announcing an article by Walter.  OM has been at this for quite a while.)  Walter's advice is similar to that of Doug DeMaw, especially on the air-core coil.   FB Walter,  thanks for sharing.  

Regarding the last line in Walter's article, please direct any complaints about drifting analog VFOs to Peter Juliano.  He will be delighted to receive these complaints, and will promptly provide all correspondents with very succinct advice on how to overcome the instability.  

My Way to a Low-Drift Analog VFO, by Walter KA4KXX

I recently built a digital VFO (from a QRP Labs Kit) to see what everybody is talking about, and it has been quite handy for my first two-band homebrew transceiver, but by the time one adds the low pass filter, a low-level RF amplifier to boost the weak output, a 5 VDC regulator, and a hefty +12VDC power line filter to the beast to keep the digital noise out of the rest of the radio, for a single band project I still prefer a low-drift analog VFO.  

My approach to minimizing drift is very simple and works well for a VFO range of 3 – 7.3 MHz, which is all that is needed for the 20 to 80 Meter bands, either direct conversion (adding a doubler for 20M) or single conversion with approximately a 10 MHz IF.  

First, see my schematic (adapted from Small Wonder Labs 40+ transceiver, original BITX40 Analog VFO, and other sources) and wind an air core inductor with stout magnet wire such as 24 or 22 AWG.  Use a thick, rigid plastic form of a diameter so that you need about 12 turns, and single coat with water-based sanding sealer, Q-dope, or similar.  Use hot glue to mount the coil firmly to the single-sided circuit board, and build a cover of some type, especially if the radio is to ever be used outdoors.
   
Second, all the VFO capacitors (except power supply bypass) should initially be the modern C0G type, which can be obtained from Mouser (such as TDK FG28C0G1H681JNT06 or the like), which I trust more than those labeled NP0.

Then, power up the VFO and tweak the coil, tuning arrangement, and range capacitor to get the frequency range you desire.

Next, monitor the drift from a cold start to see how fast it is moving as it warms up, and whether it stabilizes nicely (my goal for SSB Phone use is less than 20 Hz drift during any 10 minute period) after 10 – 15 minutes maximum.  If it does not stabilize to your satisfaction, then start substituting polystyrene caps for the C0G units one at a time until you are happy with the performance.

[Also remember that a stable BFO is important as well, and if you use the BITX 40 crystal oscillator design, I recommend installing a dedicated 78L09 power line regulator.]

If you build this VFO at the higher (7 MHz) frequency end, just change the inductor value to about 0.5 uH, with everything else about the same, but expect to do more tweaking to get stability, and the warm-up time may be closer to 15 minutes.  After years of experimenting, this is what has worked for me.  If it works for you, please send me an email (see my QRZ page) of thanks.  If not, file a complaint with Soldersmoke. 

Q-31 Quarantine Receiver -- First Signals (Video)

It still needs a lot of work, but today it pulled in its first shortwave signals.  See video.

Quarantine Rig Q-31 -- Putting the Stages Together (Most of Them)

I've been recording short videos on my progress with the Q-31 Shortwave AM Quarantine Receiver.  

Yesterday was a bit of a milestone -- I put five of the six sub-assemblies together and did some testing.  You can see the video above. 

All the other videos are on my YouTube site: 

https://www.youtube.com/user/M0HBR

Please subscribe and give me a "thumbs up." 

SITS!  Stay in the shack!  Flatten the curve.  Hang in there.   73  Bill

Other Kinds of Knack: Woodwork Wizard! (video)

This guy has some amazing tools, and even more amazing skills.  I find it inspirational to occasionally take a look at other kinds of workshops.   Check it out.  Video above. 

Along similar lines, the young Englishman Leo was in Washington state with his girlfriend when the lock-down and travel bans kicked in, so his work on Tally Ho (and his videos) continue.  See:
https://youtu.be/zXV0ywqj7zY

SITS! or Stay in the wood-shop! 

Brace Yourselves: DK7IH's New Transceiver -- The Gimme Five

Lock-down is bad enough, but now we will also have to cope with the feelings of homebrew inadequacy that Peter's rigs always cause.  But look on this as an opportunity for inspiration.  Peter once again raises the bar.   

https://radiotransmitter.wordpress.com/2020/04/11/gimme-five-reloaded-a-compact-5-band-qrp-ssb-transceiver-in-smd-technology/

This looks like it is the first in a series of blog posts. Just what we need in quarantine.   Thanks Peter.  

Videos on the Q-31 Quarantine AM SW Receiver Project (and some pictures)

I've been making some short, stage-by-stage videos of my Q-31 receiver project.  So far I have seven videos.  They are here: 

https://www.youtube.com/user/M0HBR/videos

Please subscribe to my YouTube Channel.  And give me some "thumbs up" if you like the videos. 

Thanks.  SITS!  FlattenTheCurve!  73 

Pads from Pete, toroids from Farhan

The diode ring

Altoids-sized tins will hold the circuit boards

Stay In The Shack -- Or in the front yard. 

Blog -- "Chinese Electronics Products Tested"

I was looking for information on my  FeelTech FY3200s Signal Generator.  I came across a very informative blog; it covers a variety of other Chinese gear and parts.  

Here is the Feeltech FY3200S article: 

https://chinese-electronics-products-tested.blogspot.com/p/fy3200s-function-generator-tested.html 

Here is the home page of the blog: 

https://chinese-electronics-products-tested.blogspot.com/

And here is backround information on the author: 

Thanks Jos! 

WB9IWT's Quarantine Mighty Mite and N3FJZ's "Hiram Percy Maxim Recognition Factor"

Leif WB9IWT has, during the emergency, been working on a Michigan Mighty Mite (See pictures above and below).  FB Leif.  

But also check out the very astute comment from Rick N3FJZ (below) .  I am, of course, all in favor of the HPMR Factor.  Almost all of my rigs would score quite high.    Others, I know, would seek a low score.  To each his own.  This is all for fun.  

Leif,

Great work.  If a ham from the 1920's were to see this rig, they
probably wouldn't recognize the actual components right away (but
knowing hams, they would no doubt figure it out), but the breadboard
layout circuit flow would be immediately recognizable; e.g. the plug-in
crystal, the coil, binding post.  The transistor and variable capacitor
may baffle them at first, but seeing there are three leads on the
transistor would start to give them clues.

That's the cool part about analog discrete component radio, no matter
how many years go by, and the appearance and size of the actual
components change, the physics of what's going on at the electron level
stays the same (SDR not withstanding).

I guess this could be a litmus test for us analog radio builders.  It
could be called the "Hiram Percy Maxim Recognition Factor" or "HPMR
Factor" with a range of 0 to 1.  After you  build your rig, take a look
at it and pretend that you could present it to Mr. Maxim and the more he
could understand the circuits, components and circuit flow on his own,
the closer to a factor of 1 your radio would achieve.  For example, an
SDR might only achieve a factor of .1 or even maybe 0, where as your rig
may achieve a factor of .8, and one of your crystal receivers would
definitely get a 1.

Someone could even workout a check list or formula where you would add
or subtract some fractional numeric values for each component you used;
e.g. you would subtract some value for every IC chip, microprocessor or
LCD display you use, and add some fractional value for each hand wound
coil, vacuum tube/valve or open air variable capacitor, et cetera.

Fun to think about.

Keep building.

Rick - N3FJZ

Quarantine Reading: Tribal Knowledge: Two Gems from Pete Juliano N6QW

WB9FLW recently reminded us of two very useful documents that have been kind of buried on one of Pete's web sites.   I think these documents are just the kind of thing we all need during these dark days of quarantine.  So just sit back, StayInTheShack,  and soak up tribal wisdom from the Wizard of Newbury Park.  

http://www.jessystems.com/Homebrewing%20for%20QRP%20SSB.pdf

http://www.jessystems.com/How%20To%20Stuff%20A%20Junk%20Box.pdf

Here is the message from WB9FLW that unearthed these gems:  

Morning Pete,

Three cheers for posting the Simple SSB Transceiver as a possible project during the pandemic lockdown.

Suggestion, folks that are new to your Website may not have seen some of your earlier posts especially on jesssystems.com. 

"Homebrewing For QRP SSB" is a gem and a great lead in to the simple SSB Transceiver project.

http://www.jessystems.com/Homebrewing%20for%20QRP%20SSB.pdf

There is a lot of wisdom in those pages, perhaps you can add a link for those interested in building the rig.

"How To Stuff A Junk Box" is good as well.

http://www.jessystems.com/How%20To%20Stuff%20A%20Junk%20Box.pdf

Hope you and the family are doing well.

Pete  WB9FLW

ZL2CTM Charlie Morris on "QSO Today" with Eric Guth 4Z1UG

Eric Guth 4Z1UG had a really nice interview with our friend Charlie Morris ZL2CTM.  Charlie shared with Eric a lot of wisdom about how to homebrew radio gear.  I especially liked Charlie's comments on keeping most of his rigs on the wooden prototype boards.  He said something important when he talked about the benefits of taking a break from a difficult problem, then coming back to it with a rested and refreshed mind. I noted, however,  that he said most of these frustrating problems have to do with software.  

I got got several chuckles out of Charlie's comments on the difficulty of building stable analog LC VFOs (here he seemed to be channeling our good friend Pete Juliano).  I chuckled because as I listened I was happily building the analog LC VFO for my Q-31 Quarantine receiver.  The centerpiece of this project is a variable capacitor that Pete gave me;   Pete took it out of an old  Galaxy V transceiver.   Believe me guys, no rotary encoder could possibly look as nice or have as much soul as that capacitor from Pete, with all its gears, reduction drives, and anti-backlash mechanisms.  It even smells of machine oil.  Call me a Luddite, but I will stick with the coils and capacitors.  

Listen to the interview here: 

https://www.qsotoday.com/podcasts/zl2ctm

Thanks to Charlie and Eric. 

The Low-Cost, Open Source COVID-19 Ventilator that Farhan is Helping to Build (Video)

While many of us are just trying to pass the time by building Quarantine ham radio rigs, our good friend Farhan VU2ESE has been hard at work on a really serious project:  He has been working out how to use an Arduino microcontroller as the electronic core of a simple ventilator that could save thousands of lives in the current crisis. See video above. 

Here is background info on the project (from ARRL): 

03/23/2020

Amateur radio volunteers from around the world have volunteered to assist University of Florida Professor Sam Lampotang and his engineering team in their quest to rapidly develop an open-source, low-cost patient ventilator that can be built anywhere from such commonly available components as PVC pipe and lawn-sprinkler valves. The amateur radio volunteers are developing Arduino-based control software that will set the respiratory rate and other key parameters in treating critically ill coronavirus victims.

Multiple volunteers responding to a call for help from Gordon Gibby, MD, KX4Z, included noted software developer Jack Purdum, W8TEE, and  uBITX transceiver maker Ashhar Farhan, VU2ESE. University of Florida physicians are working to address the critical legal aspects as the design moves closer to fruition.

The ventilator’s valves would precisely time compressed oxygen flow into patient breathing circuits under Arduino control, allowing exhausted patients with “stiff” lungs impacted by viral pneumonia to survive until their body can clear the infection. The software design team is also adding simple features such as an LCD display, encoders to choose parameters, and watchdog safety features. -- Thanks to Gordon Gibby, KX4Z

It is important realize that in countries around the world, many victims of COVID-19 will have no hope of getting anywhere near the kind of $50,000 ventilators found in U.S. or European hospitals.  That is one of the things that makes this low cost, open-source project so important. 

More details on the project here: 

https://github.com/afarhan/osventproto

Please pass the word on this project.  Please forward on Facebook, Re-tweet, etc. 

Quarantine Project: An AM Receiver for the 31 Meter Band. The Q-31.

During this StayInTheShack (SITS) emergency, it is good to have something to work on.  I decided it would be best to try to build something using only items currently in my parts collection.  I've been getting into shortwave listening again, and I've discovered that the 31 meter band (9.4 - 9.9 MHz) is my favorite. Thus the "Quarantine On-Hand 31 Meter AM Receiver."  A big part of the inspiration for this project comes from the AM receiver of Paul VK3HN. 

I propose that we all designate rigs built during quarantine as "Q" rigs.  This will be the Q-31. 

I had an old chassis on the shelf.  It held my WSPR DSB rig in Rome, and various other projects over the years.  It has so many holes in it that it looks like it has been used for target practice.  

A while back Pete N6QW sent me this really magnificent variable capacitor with at least two reduction dries and an anti-backlash gear.  I've been looking for a project that will allow me to use AND display this beautiful part.  It will be the main tuning cap for the Q-39. It will stay -- like the tubes in the rigs of days-gone-by --  above the chassis. 

While in London many years ago I picked up an old regen receiver at the Kempton Park rally.  The parts are still in my junk box.  A very nice 1.7 uH plug in coil (with socket) was there.  That will be the main coil in the Hartley Oscillator that will be the VFO.  I will add a few turns for the feedback coil (see circuit diagram below).  I wonder of that Eddystone coil was around for the Blitz? 

On the recommendation of our old friend Rogier (originally PA1ZZ), a few years ago Elisa got me a set of grey Altoids-sized metal boxes.  I will have three of these atop the target-practice chassis (they will provide shielding and will cover up the holes): 

-- One will hold the bandpass filter (designed with the Elsie program) and the mixer (probably diode ring, with transformers from Farhan). 

-- One will hold two IF amps with a 10 kHz 455 kHz IF filter between them (thanks to Bruce KK0S for the filters). 

-- One will hold the AM detector and the AF amplifiers. 

-- A fourth box will be under the chassis and will hold all the powered parts of the VFO circuitry.   I base my VFOs on this simple circuit from page 34 of Solid State Design for the Radio Amateur: 

This quarantine looks like it is going to last a long time, so it is best to take your time on projects like this.  I might work on the VFO today.  No need to rush... 

I am shooting videos as I go along and will at some point start putting them up on my YouTube channel.  

So, I suggest that any of you who are feeling bored and confined (that would be almost all of us) fight back by launching a Quarantine "Q-Rig"  project.   Send reports to me -- I will try to put them on the SolderSmoke blog. 

Remember:  StayInThe Shack!   #SITS!  #flattenthecurve. 

73  Bill