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Thursday, May 23, 2024

Charlie ZL2CTM's New Receiver


It is truly a thing of beauty.  

I really like that variable capacitor.  (Where did that come from?  How can I get one?)   

Charlie's calculations on each of the stages is -- as always -- really nice.  

I like the J-310 infinite impedance detector,  Charlie's use of solder wick,  the wooden base, and his decision to keep the circuitry visible.   

I also like Charlie's decision NOT to put that VFO in a metal box.  Too often we see projects that try to convince us that the receiver just won't work unless everything is hermetically sealed in submarine-like boxes.  Not true!  And Charlie's receiver demonstates this.   

Charlie is clearly keeping up the Kiwi tradition of fine homebrewing exemplified by the Tucker Tin 2,  ZL2BMI's DSB rig,  and many other FB HB projects from ZL. https://soldersmoke.blogspot.com/search?q=New+Zealand+DSB

Thanks Charlie!  Be sure to check out the rest of his YouTube channel: https://www.youtube.com/@CharlieMorrisZL2CTM

Wednesday, May 22, 2024

Rigs on Vertical Boards -- Then and Now

 
I saw this on Facebook today.  G1AVQ (SK) Rig

The G1AVQ rig reminded me of the N3FJZ rig that I worked in 2015:

I am a big fan of breadboards, and have recently been flollowing the lead of Frank Jones W6AJF in using pine boards as the bases for my homebrew rigs.  Mine are more horizontal, but we see here from N3FJZ and G1AVQ that a vertical orientation works too.  

Tuesday, May 21, 2024

Laser Communication in London 2007 -- a Pointer, a VW Solar Panel, and Radio Kismet


Hack-A-Day has an article today about using a laser for data transmission.   This reminded me of a discussion I had with Mike KL7R about similar systems.  My son Billy and I built a very simple version in London in 2007.  Check out the podcast above.  Scroll foward to 19 minutes 15 seconds and you will hear how we did this.  

This was Mike's last podcast.  He was killed in a car accident in Hawaii about 10 days later.  RIP Mike.  73 OM.  

Mike KL7R


Friday, May 17, 2024

Band Imaging Rigs (Receivers and Transceivers) -- Video from WA7MLH


In the video above (from 16 years ago) we see Jeff Damm, WA7MLH's  band-imaging receiver for 75 and 40 using an IF of 1.750 MHz and a VFO of 5.2 - 5.7 MHz,  For a signal at say 3.579 MHz (!) you subtract the signal from the VFO and you end up at the IF.  For a signal at say 7.030 MHz you subtract the VFO frequency from incoming signal and get to the IF.  (By the Hallas rule you get sideband inversion on 75/80 meters, but Jeff was on CW so this doesn't really matter.)  

Sixteen years ago this receiver was a work in progress and Jeff was having some trouble with the bandpass filters. I had similar trouble with bandpass filters. Like Jeff, I eventually got this sorted.  

I was happy to see a comment from my friend Joanthan-san on Jeff's old video.  

Jeff has an awesome and rececntly updated QRZ site:  https://www.qrz.com/db/wa7mlh

Band imaging like this is an old idea, and a very good one:  I used a slightly different scheme:   Start out planning on using a single conversion design.  Pick two bands you are interested in.  Select an IF midway between the two.  Build a single VFO that --when added to the incoming (or the outgoing) signal will get you to one of the bands, and when subtracted from the signal will get you to the other one.  Bob is then your uncle.  Two bands, with minimal switching. 

I got started with band switching with my Mythbuster rig:  I would get 75 and 20 meters.  The IF was midway between the two at 5.2 MHz.   My VFO (from an old Yaesu FT-101) ran around 9 MHz.  Boom, it worked, with the added benefit of receiving and transmitting LSB on 75 and USB on 20 with no switching of the BFO/Carrier Oscillator.

Then I did 17 and 12 meters.  Kind of a WARC-band special.  IF was at 21.4 Mhz.  VFO ran around 3.5 MHz.  So by adding the incoming modulated signal 18 MHz signal and the VFO, you get to 17 meters.   By subtracting the VFO from the incoming 24.9 MHz signal you get to 12 meters.  And both are on USB (apply the Hallas rule), so again, no switching of BFO/Carrier frequencies are required. 

Finally,  at solar max, I built rigs for 15 and 10.  Here the IF was 25 MHz.  Again the VFO was around 3.5 MHz.  Adding the incoming 21 Mhz signal to the VFO gets you to 25 MHz, subtraction of the VFO frequency from the in coming 28 MHz signal takes you to 25 Mhz and thus 10 meters.  Again, no sideband inversion (Hallas rule).   Both signals are USB and stay on USB. (I built two versions of this rig -- one stays in Virginia, the other is heading to the Dominican Republic.) 

In the ARRL book QRP Classics, there is an article from the 1990 Handbook entitled "A Band-Imaging CW Receiver for 10 and 18 MHz."  The article may have been based on a receiver built by Dave Newkirk AK7M (Rod Newkirk's son). Unfortunately in the write-up for the ARRL handbook, the drafters repeat the oft-repeated myth about how 9 MHz IF and a 5.2 MHz VFO would supposedly produce LSB on 75 and USB on 20.  This just doesn't work.   But if you put the IF at 5.2 MHz and the VFO at 9 MHz, it does work, as demonstrated by my Mythbuster rig. 

Thursday, May 16, 2024

A Light-beam QSO in Hollandia, Christmas 1944


This old QST article caught my eye, largely because my father was also in Hollandia on that  Christmas day in 1944.  He was in the Navy hospital there, recovering from wounds received in the battle of Leyte gulf (in the Philippines).   Hollandia, also known at Humbolt Bay, is now Jayapura, Indonesia. The picture above shows the harbor in 1944.  Rod Newkirk W9BRD went on to write QST's inspirtional "How's DX?" column for many years. 
----------------- 
From S/Sgt. R. H. Newkirk, W9BRD, "Christmas, 1944" QST, January 1946, pages 25 and 102.

Christmas, 1944


In a wartime world the singular and exclusive camaraderie that exists in the hobby of amateur radio results in so many unexpected and coincidental meetings between good friends, who have previously never seen each other, as to make such happenstance fairly commonplace. But I boast a tale in which time, place and circumstance combined to cause a similar occurrence to be most extraordinary.

The Liberty ship El Segundo Ruiz Belvis lay at anchor in the murky waters of Humbolt Bay, New Guinea, on a tepid tropical night in '44. In the absence of the moon, the Dipper and the Southern Cross scintillated bewitchingly. On the shore, the lights of the army base of Hollandia burned steadily in contrast to the varipowered signal blinkers which intermittently pieced the opaque darkness throughout the harbor. The latter were visual communication between ships and shore plus an admixture of ship-to-ship chatter, official and otherwise. There was an underlying tense tinge to the atmosphere and the stillness was broken only by the sharp staccato of the Belvis' blinker shutters as the signalman transacted port business with the powerful land station.

This was rendezvous. Our Liberty, with scores of army personnel aboard, had here become a unit in the formation of a huge convoy. Crammed into holds, on hatches and into every available nook and cranny of the steel deck, we were Leyte-bound. Stifled, sweaty and hungry on our two meals per day, we wore out deck after deck of pinochle cards and read every available piece of literature over and over again. It was almost a month since we had left Sansapor, scene of our last operation. We were exuberant in the knowledge that we were soon to leave New Guinea.

Christmas was but a few days away and we had had no mail for weeks. Men leaned languidly on the rail and thought of home while others dreamed of the same in their cramped quarters. The circumstances certainly made this Yuletide one to be long remembered. Nevertheless, all that would feature this day for us would be a possible piece of priceless turkey added to the usual dehydrated viands. Just another dragging equatorial day to be piled atop hundreds of others like it.

It was ten o'clock. I was wide awake; only my eyes were tired. Presently, I found myself detachedly reading the blinkers which poked their focused fingers indiscriminately about the bay. My quarters, in the cab of a 399, were on the port rail amidships and afforded a good view across the water. I became absorbed in various bits of chatter between nearby vessels. It struck me that QRM was quite heavy tonight—a sort of an optical 80 meters. I saw one of the lights sign off with a "73." This was interesting as among the host of merchant marine signalmen, hams are spread pretty thinly. I seized my M-1 torch and focused an insipid beam in the direction of that ship. I sent CQ CQ CQ K. A ham call sign is a cumbersome thing to handle with a blinker. Furthermore, I had no faith in the DX powers of my 3-volt flashlight bulb. I was therefore elated when a bright interrogatory sign beamed forth, aimed obviously in my direction. Contact! True, it was outside the hambands, but band divisions in the microwave region are indefinite anyway.

I was still dubious as to whether my man was an amateur. Rather than complicate matters immediately, at this speed of 8 words per minute, I began in the language of the layman: HELLO PAL WHERE YOU FROM? K. Back in an agreeably rhythmic style came: R TULSA OKLA NAME IS HAL K. The given name and place struck a subconscious inner chord vaguely. Next, I blinked: GE HAL IM ROD FROM CHGO K. There was a pause. He reoriented his beam to compensate for tidal drift and then startled me with: W9BRD DE W5EGA K.

The night quickly took on an exhilarant aspect as we lapsed into ham vernacular, spiced with many Morse slaps on the back. Hal Frank was no other than an old c.w. crony of mine. We had heckled each other on 80, 40 and 20 a countless number of times in the prewar days. In memory I was hearing again that beautiful swing and T9X sledge-hammer signal off his three-element rotary. We discovered mutual ham friends and we exchanged much welcome information and recounted bygone days. He was quite amazed to learn that I was behind a mere GI flashlight (with low batteries at that). The QSO continued far into the night—the next and the next.

We seemed destined to rot in our anchorage. The convoy movement was postponed from day to day. However, this Christmas season took on a much different aspect for me as arrangements were made and, at 0900 Christmas Day, my friend, Wilbur Kuure, W9YNY, and I debarked unsteadily down the ladder and made our way across an undulating swell to the Liberty ship Chittenden. There, we met Lt. Hal Frank, W5EGA, personally, for the first time. We all agreed that it was quite a small and bizarre world that December 25th.

Verbal reminiscences cluttered the air within W5EGA's exceedingly neat cabin for several hours. Shelves in his quarters were lined with excellent reading material including many late QSTs. Compared to our situation aboard the Belvis, Kuure and I thought this a bit of heaven.

We were thoroughly acquainted by the time we appeared in the officers' mess. As the cuisine took shape before us and disappeared into our eager gullets, my army pal and I felt somewhat sorry for our less fortunate buddies on the home ship. But such is life. We had, in nautical terms, a "Little Roundhouse," consisting of a generous helping of everything on the menu. We swept our plates clean to Hal's amusement. I remember, most distinctly, the dessert of apple pie and ice cream.

Nightfall found Kuure and me "back to earth" on the Belvis after a most delightful Christmas Day. According to plan, we blinked a "goodnight and thank you" to W5EGA through the twilight. That was our last QSO of that series. Not long after that we weighed anchor and headed for our next stop on the long road back home. Our holiday was over, a new year had begun and there was still a war to be won.


From S/Sgt. R. H. Newkirk, W9BRD, "Christmas, 1944" QST, January 1946, pages 25 and 102.

Wednesday, May 15, 2024

CuriousMarc Looks at Phase-Locked Loops (PLL)


I really like Marc's (AL6JV) videos. It is great fun and very educational to watch him and his team troubleshoot some of the old gear they work on.  There is also a lot of humor. 

In this video Marc delves into the circuitry of the Phase-Locked Loop.  I didn't know that the PLL circuitry has its origins in the space program.  NASA needed a circuit that would permit very narrow band reception of a signal that was undergoing the kind of Doppler shift that spacecraft produce.   Viola! Enter the PLL.  Far beyond Apollo, PLL circuits started to show up in ordinary radio gear.  The General Electric (and JC Penny!) CB transceivers that we rescued from 11 meter infamy used PLL as the frequency determining circuit. 

Marc gives a really good explanation of how the PLL circuit works.  Thanks Marc. 

However, Marc gives an incorrect pronuniation of "kludge" (it should sound like fudge).  But he is a computer guy and is originally from France, so all is forgiven.  He also redeems himself by making fun of the inaccuracies that appear in what he calls "data shites." 

Monday, May 13, 2024

Ragnar LA1UH's Wonderful Museums in Norway



Here are two more great museum visits by Helge LA6NCA.  In these two he visits Ragnar LA1UH.  

Ragnar has a lot of maritime experience, so we see a lot of older ships' radios.  But his interest in the radio art is much broader and we also see a lot of other kinds of gear: 

-- Wow,  a "travel radio" in a suitcase from 1927.  Was this the idea that later lead to the Parasets of WWII? 

-- Lots of "Stay Behind" gear from the Cold War. That "Africa" receiver (that never made it to Africa!) is very interesting. 

-- We see an ART-13 with autotune, ANGRC-9s, several ARC-5 command sets.  I was hoping Raganar would fire up a Dynamotor, but no. 

-- I spotted a Galaxy V transceiver.  I have the VFO reduction drive from one of these in my homebrew 15/10 rig.   

-- We see several variometers in the emergency (500kc?) maritime transmitter.  I used a variometer in my super-simple ET-2 transceiver (with an N0WVA receiver). 

-- Lots and lots of tubes. 

Ragnar says he himself is of 1944 vintage. I hope some "stay behind" provisions have been made for these amazing museums. 

Thanks to Helge LA6NCA and to Ragnar LA1UH.  

Saturday, May 11, 2024

Jens OZ1GEO's AMAZING Radio Museum



Brace yourselves.  This is just too much, too much radio history, too much cool stuff.  We are into ham radio sensory overload territory here. The rigs, the radios, the radioactive stuff (including tubes!).  Lots of Whermact stuff.  A Chinese receiver.  Tesla coils and Faraday shields.  Much more. 

Thanks to Helge LA6NCA for alerting us to this and for shooting these videos.  And thanks to Jens OZ1GEO for putting this magnificent collection together.  I hope they find sometplace to keep this all together so that future generations can benefit from it. 

George WB5OYP points out there is more from Jens here: 

Helge SM/LA6NCA Activates Colorburst Liberation Army in Sweden!


FB Helge.   This is really cool.  I didn't realize until I saw the schematic at the end that he was on 3579 kHz -- that is the old color-burst frequency, and now the frequency of the Color-burst Liberation Army. 

It was challenging to do this without sidetone.  But there appears to be a bit of room left in the matchbox -- could he squeeze in a few more components for a rudimentay sidetone?  Maybe just a piezo buzzer across the key? 
VIVA EL CBLA! 

Friday, May 10, 2024

Wednesday, May 8, 2024

Why we have "BW Limit" Switches on our Oscilloscopes

Dean KK4DAS asked me why we have these switches on our 'scopes.  I didn't know.  Dean asked Alan Wolke W2AEW.  Alan knew: 

Alan Wolke wrote: 

Interesting background on the 20MHz vertical BW selection. This feature has existed on the vast majority of all oscilloscopes since the 50s or 60s (both analog & digital). When I explored the history of this, I spoke to some of the folks at VintageTek.org, and wound up having a chat with THE engineer that did it first!  Tt was John Addis, designer at Tektronix. 

At the time, Tektronix was located in Portland Oregon. While working on a wideband vertical preamp for a new scope (the 7A11 vertical plugin for the 7000 series scope), John Addis was plagued with interference from the local television broadcast station in the 50MHz band. So, he popped in a 20MHz low pass filter that he could switch in/out so that he could complete the work on the preamp. Since it was deemed useful, it was left in the design. 

 

And, since Tektronix added a switchable 20MHz low pass filter  in their scope, and Tek was the leader in oscilloscope technology, other manufacturers followed suit, and this feature has "stuck" as a staple in vertical setting controls. 

 

The main reasons you'd use this filter would be to improve the signal to noise ratio (SNR) for signals when their frequency content is below 20MHz.   You've probably noticed that, even without any signal connected, the thickness of the trace is thinner when you engage the 20MHz filter. 

---------------------


Alan sent a link to a Wiki page about the 7A11 that John Addis was designing.  Alan says this places the initial inclusion of the 20 MHz BW Limit filter to the mid 1960s: 


https://w140.com/tekwiki/wiki/7A11



Thanks Dean, thanks Alan!  

Saturday, May 4, 2024

W4YWA's Homebrew Rig on 20 Meters

 

Ed W4YWA is far too modest -- he has built a very FB homewbrew transmitter.  Congratulations Ed.  I think your original plan to use a Web SDR receiver will work, if you and the other station are just willing to pause for an additional second or two to let the internet catch up with the real world.  Also, you might find some Web SDRs that have less latency than other.  You could used a little SW receiver or a simple buzzer for your sidetone ( I think sidetone is your most pressing latency concern.)   My suggestion is to try to get a few contacts using the Web SDR (perhaps via schedule -- try the DX Summit or the SKCC web page to set some up). Then build yourself a simple Direct Conversion receiver to use with this rig.  You don't have to try to build a VFO at 14 MHz (that can be difficult) -- you could build one at 7 MHz (use the circuit from our High School receiver project) and pair it up with a "Subharmonic Mixer" so that you can tune the 20 meter band.  Please keep us posted on your progress. 

Ed writes: 

Home-Brew Fun and Failures 


I’m not much of an amateur radio operator, but I enjoy the electronics, self leaning, and the home brewing aspects of our hobby. Here’s an account of a recent effort. While trying to re-learn CW, I discovered web-based SDR sites with waterfall displays, all kinds of filtering and better performance than any of my vintage station receivers. So, I start thinking….. if I had a little transmitter and a simple antenna, along with internet access, I’d have a capable station to take on vacations to the beach. Yes I know, there are web based amateur radio stations, but remember the operative words here are: “Home Brew.” After pinging the Google machine, I came up with a two-stage 1-1/2 watt transmitter sometimes refereed to as the “Universal QRP transmitter,” or the “Little Joe Transmitter.” There’s lots of variations of this circuit but it is essentially a Colpits crystal oscillator coupled to a class-C PA. I chose 20 meters because I didn’t want to hire an arborist to string my antenna. My design modifications included a transistor switch that keys both the oscillator and PA, a VXO circuit, power transistor protection, and a 5-th order Chebychev low pass filter.

Notice the (do I dare say, good looking?) enclosure. In a former life, it was a SD card reader from a defunct PC. FYI, gutted CD/DVR drive cases also make fine enclosures for your home brew projects. I opted for a “foil side up – without holes” for my PCB design. All the parts are soldered down on the lands - no PCB holes. I wanted to change parts without having to do open heart surgery. Functional placement was also important to me. I took more time than I’d like to admit to organize the circuit layout as I did, but I’m glad I did.


When all was said and done, it was time to power it up and….. and …. nothing! Not a single function worked! I won’t bore you with the debug stories that took forever, but the only part I didn’t have in my junk box was the PA transistor. I got 10 of them for $5 off the Internets and they all failed to deliver. I could only get a few tenths of a watt from my design. In a fit of desperation, I un-soldered a PA transistor from an old CB radio and it immediately gave me 1.8 watts of pure CW ! ! ! ! Happy dance, happy dance! But, save your accolades. There were lots of other problems; they were my problems not component issues. For example, before you design your own RF filter be sure you understand cutoff frequencies. They are not the same for every filter design. I suggest Paul Harden’s NA5N site to learn about PA output filters. My first few filter attempts had the transmit frequency well down on the attenuation curve. I was attenuating my own signal ! So, after weeks of “why don’t the damn thing work,” I got a clean signal. Whoo-Hoo!


Now it was time to unshackle the dummy load and see where I can be heard. And, Oh boy… I’m beaming into Pennsylvania, Georgia and Northern VA, all from an inverted V on a tripod mounted paint stick, held apart with two tent stakes. But then, reality took over. My grandioso plans for using the web-based SDRs as a station receiver (and the side tone oscillator for my transmitter) didn’t account for the latency delays of the SDR software. If you ever listened talk radio and the host says, “Turn your radio off – the delay will make you sound like a ….” you know what I’m talking about. You would think that someone who over thinks everything, would have foreseen this issue before spending countless hours of breathing solder fumes? Humility and eating crow are my better traits. But not to worry, I’m not ready to give up. Stay tuned for more adventures of Home-Brew Fun and Failures. 

73s W4YWA

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