Category: AM

SolderSmoke Podcast #217 — Beach trip, ’30s station, uBITX mods, HRO RX AM, ELMAC, Teensy, MAILBAG

Bill’s Bavaro DR Beach Station
uBITX in the box, HB key
SolderSmoke Podcast #217 is available:


1 February 2020

Travelogue! Dominican Republic trip. uBITX on the Beach. EFHW. LiPo Battery. First contact of the new year.

Bill’s Bench Report

Following up on proposed uBITX mods:
— Put pot on sidetone line from Raduino to keep the sidetone a bit quieter.
— Fixed the key — pounding brass
— Will install 4 States QRP Active AF filter.
— Need to reduce power on CW to 5W
— Stereo to mono headphone adapters.
— Turning off display and mic amp circuit not really worth it — they don’t pull much current.


Pete’s Bench Report:
ELMAC Power Supply project
1930s era transmitter?
Teensy and SDR
PETE’S IDEA ABOUT GETTING LSB AND USB FROM BITX40
KWM-2 suggestions

Back to Bill’s Bench:

Working on HRO-ish Receiver.
Bad SBL-1
Got idea for wider ceramic filter from Paul VK3HN
Ordered parts from Mini-kits in Australia. They sent 6kc filters.
Bruce KK0S sent me some 10 kc filters too.
Installed 6 kc filter with L network matching networks. Works great.
Also installed Infinite Impedance Detector that Paul used.
Needed some additional amplification ahead of the IID, so I used one stage of BITX amp.
Works great. I can tune full 40 meter band AND 49 meter SW band. Radio Romania, China, Radio Marti, Brazil, South Carolina.
Beefed up the shielding to cut down on AM detection.

MISCELLANY
— AM and DSB in LTSpice
— Duly Noted: Paul VK3HN’s RIG: “THIS MACHINE KILLS KILOWATTS”
Kanji YC3KNJ’s QRPesso Expresso Coffee in the field
— The DANGERS of powerful magnets.

MAILBAG:
–KK4DAS Dean doing great things. MMM heard at Penn State. Where is the rest of the CBLA?
— Thanks to Don for kind donation to the SolderSmoke cause
— Dale BA4TB — First SolderSmoke feedback from China. Thanks Dale!
–Steve Silverman: Sideswipers and bugs were made to handle “carpal tunnel of the day” So do I need a keyer for casual CW work?
— Peter VK8VWA on the limited knowledge gained from kit building. Listens to podcast while walking on the beach in Australia.
— Allan Hale — Clothes Pins as Toroid holders. Yes! More Clothes Pins Wild Woody Keys from Dave Ingram
— Pete WB9FLW 100 Watt Amp from WA2EUJ
— Dave Wilcox K8WPE A medical question: Does the Michigan Mighty Mite work differently depending on what kind of medicine was in the pill bottles used for the coil form? Good question Doc! Dave suggest that putting CBD on the coil or the crystals. Anything to mellow out the ham bands…

Pete’s Plank SDR
When you know stuff, you can do stuff!


How to Generate an AM Signal (and DSB!) in LTSpice

Pretty cool and very useful. You can also do this by using the Modulator symbol, but I found this technique easier and more straightforward.

But be sure to watch all the way to the end of the video. Early on, he forgets the step that causes the carrier to stay in the simulation, but then shows how to correct this. In the process we learn how to create a DSB (suppressed carrier) signal in LTSpice.

Lebanon’s First Radio Website

I found this site through Paul VK3HN. He took the AM detector circuit for his AM receiver from one these Lebanese homebrew radios.

There is some really great information on this wonderful website. It has been online for some 20 years — I wish I had found it earlier. The author shares his Knack story — this is a wonderful example of the International Brotherhood of Electronic Wizards (IBEW).

http://www.midcenturyradios.com/index.html

And he has very cool schematics, really well done. Click on image to enlarge:

VK3HN’s Inspirational AM Receiver (video)

I’m always delighted when I check the SolderSmoke blog and YouTube list (right hand column of the blog) and find a new post from Paul VK3HN. And this morning’s post is especially good.

Paul has built an AM receiver. Above you can see his video. Here is his blog post with details:
https://vk3hn.wordpress.com/2019/12/06/8-band-superhet-am-receiver/

 This is the kind of blog post that makes you want to heat up the soldering iron and start searching through the junk box. I’m thinking about putting Paul’s 6 kHz filter in my 40 meter HRO-ish receiver. And I may make use of his AM detector circuit. And maybe I can put that same receiver on 75 and 160… And then there are the SW broadcast bands… See what I mean?

Thanks Paul. 73

HT-37/2B QSO with K6ZA (three short videos)

On January 23, 2019 on 20 meters I talked to Barry K6ZA. He is near San Francisco. I was running my Hallicrafters HT-37 with my Drake 2B. I was really pleased to discover that the guy I was talking to loves these two pieces of gear as much as I do.

Barry said he wished I could record his voice coming out of the HT-37. My iPhone came to the rescue.

EF Johnson’s 50th Anniversary Speech. Very nice radio history

Thanks to W0VLZ for this wonderful 13 minute recording of Edgar F Johnson’s 50th Anniversary speech. There is a lot of great radio history in this speech. Highly recommended.

Just click here to listen:

https://www.prismnet.com/~nielw/EFJohnson/EFJ50thTalk.wav

EF Johnson’s hometown bio:

http://www.wasecaalums.com/public/389.cfm

NN2K’s Beautiful Pine-Board Al-Fresco Thermatron AM Transmitter

On Saturday mornings (around dawn) I often listen to the Old Military Radio Net on 3885 kHz. I find it inspirational. This morning the inspiration was provided by Rick NN2K. His signal from Binghamton New York was makeing the trip to Northern Virginia. When I heard him mention that he was using a “Pine Board Transmitter” I felt the urge to look for a picture. QRZ.com provided the photo.

Rich says he built this rig in January 2018 based on a QST article by Bob Heil. FB Rich!
And thanks to Ted W3PWW for running the Old Military Radio Net for so many years.

Mike Rainey and Heavy Metal AM Phone

Michael Rainey AA1TJ wrote:
I can tell you exactly what’s going on here. I’d just received a license upgrade from “Novice” to “General.” My new license granted radiotelephone privileges and I was eager to try them out.

In the early 1970’s no self-respecting amateur radio operator would dream of using amplitude modulation (AM) on wavelengths above 10m. It wasn’t illegal, rather, it was frowned upon due to bandwidth issues, among other things.

But in my excitement – and in the time-honored spirit of, “don’t ask permission, ask forgiveness” – I tuned my clunky, Heathkit DX-100 to the 40m radiotelephone band and began calling CQ on AM. Everyone that I contacted was very polite, but to the man they all mentioned how “odd” it was to hear an AM signal on 40m. I eventually took the hint, but not before I’d figured out that yakking on a microphone wasn’t my thing after all. Morse telegraphy was my first and enduring love.
————————————-
I think Michael’s next phone transmitter was that voice-powered rig that he used in an attempt to cross the Atlantic with the only power source being his vocal cords. But even there, he was using his voice to send Morse.


C’mon back to radiotelephone Mike. There is more to life than dots and dashes!

Thermatrons Al Fresco: W4GON’s FB HB AM Rig

I was listening to 7290 kHz with my BITX this morning and I heard W4GON say his AM rig is homebrew. So of course I fired up the DX-100 and the HQ-100 and gave Joel a call. Conditions were terrible but we had some support from the radio gods.

From Joel’s QRZ.com page: “It uses a pair of 6L6s in Push-Pull Class AB1 high level plate and screen modulating a 6146. I still have a lot of work to do on this rig, like building an enclosure, but it works and I just couldn’t help but getting on the air with it!”


I think it is a thing of beauty.

Intuitive Repair of a Sony Shortwave Portable

A few years ago my wife got me this nice little Sony ICF-SW7600GR receiver. On the front it proclaims that it is “AM DUAL CONVERSION” and “PLL SYNTHESIZED.” It has a BFO, and a filter of suitable width for SSB. It also has a synchronous detector — it generates an internal carrier that matches the frequency and phase of the carrier being transmitted by the SW broadcast (or ham AM) transmitter. This helps overcome the selective fading that often plagues AM signals. Sony advises switching to USB or LSB once the synchronous generator locks onto the carrier. Pretty cool.

The BFO is the reason I wanted this receiver. And wouldn’t you know, when I dropped it, it landed EXACTLY on the little BFO fine tune control pot. It was as if the Radio Gods disliked all the fancy digi PLL synchronous IC circuitry.

I tried without success to find the value of the destroyed pot. Finally, last week I just decided to have a look in there to see if I could just figure it out.

On the board I could see that the pot only connected at two places, so I figured it would be a varactor circuit on the BFO with one end of the pot to DC and the wiper to the varactor diode. I figured I’d try a 10K pot.

This seems to have been some good radio intuition. It works. I went with a small trimmer because it is less obtrusive and because once I set the BFO in the right spot, I think the de facto channelization of the 40 meter ham band will keep most of the SSB sigs in tune. And the Sony only tunes in 1 kHz increments. If necessary I can move the BFO a bit with a small screwdriver. I just glued the trimmer pot onto the back of the receiver — two wires covered by heat shrink run back into the circuitry.

10k might be a bit too small. Maybe 100k would be better? As it is, I can move the BFO above and below the “zero beat” point, and I don’t need more range. Mouser has a small trimmer pot with a tuning wheel that looks like it might fit, so I may try for a proper repair.

Stepping Inside an AM Transmitter (video)

Very cool video. We have visited VE7ZWZ’s amazing shack before. This time he takes us inside a BIG commercial AM transmitter that he has modified for use on the amateur bands.

I know that he had the plate voltage turned off, but I still felt myself cringing when he reached up to touch the plate connectors on those enormous thermatrons. The filaments were on, adding to my unease. Dude, don’t do that! And if you are standing INSIDE the transmitter, keeping one hand behind your back might not be as beneficial as it normally would be.

His comments on his VFO were interesting. I was kind of disappointed that he went with a varactor circuit. A varactor? Amidst all those bread slicer variable caps? It just doesn’t seem right. (And BTW they are bread slicers, NOT “potato slicers.”) But I kind of liked the heater–thermistor–insulation set up that keeps the VFO at constant temperature.

I thought it was interesting that these transmitters were kept on, with the tubes glowing for years at a time.

Thanks Mr. Carlson, for another great video!

WU2D’s Wonderful Video on Retro-QRP

(Link to video appears below.)

 Stephen G7VFY sent me the link to Mike WU2D’s Retro-QRP video. In the last month spoken to Mike at least twice on 40 and 75 meter AM. Stephen was responding to a post I did about a 1958 18 milliwatt solid state QRP rig.

Mike’s video is really wonderful. I’ve never been into military surplus, but this video made me think I might want an ARC-5. The rig Mike builds and tests is very similar to our beloved Michigan Mighty Mite. His description of the build and the testing procedures he used will be of great interest to those who’ve built the MMM rigs. And he made some contacts. Finally, there is a cameo appearance by Paris Hilton. And she is holding a HOT transistor! Wow!

Mike has a real talent for making these kinds of videos. Thanks a lot Mike — see you on 40. And thanks Stephen (Stephen has sent us so much great stuff over the years, including a fantastic box of British valves.) Pete: See how nice it is to get back to QRP?

Here’s Mike’s YouTube Channel. I love the intro:
https://www.youtube.com/channel/UCN7RQv_qmzhzuJV1HhJ4OEA

VE7SL and THE POWER OF THE GREEN GLOW

Steve VE7SL recently discussed Heathkit’s wise use of the color green in the VF-1 and DX-100 frequency readouts. The power of green is visible in the above photo of the N2CQR AM station. (I used this gear to check into the Old Military Radio Net and the Lonely Guys’ Net on 75 meters on Saturday). Note the VF-1 on the shelf in the upper left, and the awesome green oscilloscope trace. Juliano Blue is all well and good, but let’s not deny THE POWER OF GREEN.

Steve’s discussion (and cool Knack story):

http://ve7sl.blogspot.com/2017/01/the-green-glow.html

75 and 40 Meter AM on my HQ-100 (Videos) + Digital Display

And here is how I sample the oscillator frequency for the digital counter. I use an old trick: I wrap some wire around the oscillator or mixer tube. I made the coil out of an old coil form. I had to play around with the number of turns to get suitable pickup on both 160 and 40 meters. The San Jian board allows for IF freq offset. I use a similar arrangement on the transmit side with the DX-100. By the way, the box that houses the two displays is the carcass of one of the Heath QF-1 Q multipliers from which I heartlessly pulled the nice reduction drive variable caps for use in my BITX rigs.

Add caption

Inside the Hammarlund HQ-100

I continue to work on this old beast. I picked it up in the Dominican Republic around 1994. One of the IF transformers had gone open. I fixed that. Had to replace the AF output transformer too. And the variable cap that tunes the antenna. Check out the flywheels! And the rope and pulley thing. You don’t find those kinds of things in any of those fancy modern rigs.

Earlier I had removed “the exclusive Auto-Response audio output circuit.” See:
http://soldersmoke.blogspot.com/2016/02/snowed-in-audio-mods-on-hammarlund-hq.html

 Today I installed a simple feedback network in the AF amplifiers (as prescribed here:
http://www.amwindow.org/tech/htm/hqaudiomods.htm

 It sounds nice now. The rest of the bands have been ravaged by some sort of solar event, but 160 seems to be benefiting — signals last night and this morning were quite strong. I was being heard by WA1HLR way up in Maine.

UPDATE 20 Feb 2016: After installing the feedback network mentioned above, I noticed a big increase in AC hum. It was not the electrolytics. I reversed the feedback mod and the hum went away. But the receiver continues to sound a lot better with the removal of the Auto-Response output circuit.

Snowed In! Audio Mods on the Hammarlund HQ-100

It is snowing here today, so I am stuck in the hamshack. YEA!

I’ve had the Hammarlund HQ-100 receiver on the bench because I am building an outboard digital frequency readout for it and for the DX-100. More on this later. But as long as I had it on the bench I decided to do a mod to the audio output that has LONG been needed.

Here is a nice web page that describes the problem and the solution. The problem is the “Auto Response audio output circuit” touted in the add up above. Essentially I had to remove the touted circuitry. The AutoResponseectomy only took me about 15 minutes and the results are quite noticeable. The old receiver sounds a lot nicer. I’m listening to 40 meter AM now. FB.

Here is the page:
The HQ-100 does indeed have “three dimensional beauty.”

A Snow Day Well-Spent: Chris Modulates an AD9850

Feb 10 at 7:40 AM
Hi Bill and Pete,
My work is closed today due to the snow so I wanted to show you what I’ve been up to.
I built sort of a test fixture a while back for those cheapie EBay AD9850 boards based on AD7C’s DDS circuit using an Arduino Uno as a controller.
Last summer someone posted a link to Analog Devices App note AN-423 on QRP-Tech I think.
It was always on my list of things to try.
Armed with a schematic of the eBay DDS gleaned from Doug Pongrance’s website, I got to work. It involved cutting a trace or two on the DDS board using an X-Acto knife.
Two outputs of the DDS chip are fed into a wideband transformer as in the app note’s second page and I hung a scope probe off the secondary of the transformer.
Basically you are removing the Rset resistor on the DDS board (marked R6 on mine) and using a 2N7000 MOSFET as an electronic version variable resistor and modulating the MOSFET.
This lead to much frustration over the afternoon. No output on the scope!! Did I make an error or connect something up wrong? I was using the 600 ohm output of my HP652A audio generator. I thought about it during lunch and decided to try the 50 ohm output. Bingo!! At the 3V RMS range setting on the generator I now have some kind of signal. Not a nice sine wave shaped AM output but at least something resembling a clipped sine wave. The circuit is really touchy as far as needing a hefty audio signal in. The output of my iPhone at max volume doesn’t turn on the DDS chip.
I set the DDS for 1200 kHz and can listen to it on a Radio Shack portable radio. Varying the audio generator varies the received tone on the radio just like I was expecting.
I just need to figure out what’s up with the audio levels.
Chris
KD4PBJ