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Monday, July 19, 2021
Michael Newton Hopkins, AB5L, Author of the FMLA series
Tuesday, June 29, 2021
Jack NG2E's Pebble Crusher
Check out NG2E's Pebble Crusher homebrew transmitter. Doug DeMaw would be enormously pleased.
Jack will no-doubt have this 250 mW rig on the some peak along the Shenandoah Valley, handing out QSOs to SOTA fans.
Jack's blog page has a really nice video on this project:
https://jackhaefner.blogspot.com/2021/06/pebble-crusher-40m-xmtr.html
Monday, June 14, 2021
M0NTV's Latest FB SSB Transceiver
Saturday, February 6, 2021
Some Thoughts on Singly Balanced Mixers with Two Diodes and One Transformer
Thursday, December 31, 2020
So Many Wonderful Things on W7ZOI's Site
There he is. Wes Hayward, W7ZOI in 1957. I had never seen this picture before. I found it on Wes's recently updated "shackviews" web page: http://w7zoi.net/shackviews.html .
There are so many treasures on that page, and on all the other portions of Wes's site.
Some highlights for me:
-- Wes's description of the station in the above picture.
-- On his page about Doug DeMaw, Wes mentions that after Doug edited Wes's 1968 article about direct conversion receivers, Doug built some himself, experimenting with different product detector circuits. Having used Doug's mixer circuit in many of my rigs, and having recently experimented with different product detectors for my HA-600A, I kind of felt like Doug was watching over my shoulder, guiding me along as I experimented.
-- Wes's use of a digital Rigol oscilloscope. Makes me feel better about giving up on my Tek 465.
-- The page about Farhan's visit to Wes, and the awesome gathering of homebrew Titans that ensued...
-- Wes's meeting with Chuck Adams.
Thanks Wes. Happy New Year and best of luck in 2021!
Monday, November 9, 2020
Improving the Product Detector in the Lafayette HA-600A
Steve N8NM built the HA-600A product detector both in LTSpice and in the real world. It worked fine in both versions. Steve even put the product detector into his S-38 receiver -- he reported it worked well there.
I too built the thing in LTSpice. Then I went and rebuilt the circuit on a piece of PC board. I connected the new circuit to the HA-600A, using my external FeelTech sig generator as the BFO. IT STILL SOUNDED BAD ON SSB.
At this point I started Googling through the literature. I found a promising article by Robert Sherwood in December 1977 issue of Ham Radio magazine entitled "Present Day Receivers -- Problems and Cures." Sherwood wrote:
"Another area that could use additional work is the product detector. As the name implies, its output should be the product of the two input signals. If BFO injection is removed, output should go to zero. If this is not the case, as in the Heath HW series, envelope detection is also occurring, which causes audio distortion."
I checked my circuit. When I removed the BFO signal from the product detector, envelope detection continued. In fact, with the receiver in SSB mode, and with the BFO disconnected, I could listen to the music of WRMI shortwave. It seemed that Sherwood was explaining well the problem I was having: Simultaneous envelope and product detection was making SSB sound very bad in my receiver. What I was hearing just seemed to SOUND like what you'd get with a mixture of product and envelope detection: "scratchy" sounding SSB. This also seemed to explain why SSB would sound fine when using the diode detector with loosely coupled BFO energy -- in that case it would be envelope detection only, with no ugly mixture of both kinds of detection.
Finally, I needed to find a way to use the BFO in the HA-600A with the new product detector. Obviously I needed more BFO signal -- I needed about 7 dbm, enough to turn on the diodes. I converted the outboard product detector board into a simple amplifier and put it between the HA-600A BFO and the BFO input port of the new product detector. This works fine.
A few issues remain:
1) The output from the HA-600A BFO through the above BFO amp (and across the 50 ohm resistor) is NOT a pretty 455 kc sine wave. But the peaks of the distorted wave appear to be enough to turn on the diodes, and when I look at the voltages across each diode (on my two channel 'scope) I see mirror images -- one is on when the other is off. Is this good enough?
2) Moving the BFO input from L1 to the junction of the two 50 ohm resistors (that is actually a 100 ohm pot) has big implications for how this mixer works. With the BFO energy going through the toroid, BOTH diodes are being alternately turned on and turned off. But both are on, and then BOTH are off. With the BFO energy going in through the other side, one diode turns on when the other is off. I think the mixing result is the same, with AF coming out of the output port, but the way the mixer works in this configuration is very different. Does this sound right?
Friday, August 21, 2020
The Original Tuna Tin 2 (and the Mojo Transfer Ceremony with W1REX)
-----------------------------------
Here is my only encounter with the original Tuna Tin 2 -- In 2014 Rex W1REX conducted this solemn ceremony in which some of the TTT mojo was transferred to my homebrew BITX 17.
Sunday, August 9, 2020
Presence (Absence?) and Direct Conversion Receivers (with wise comments from Farhan)
Farhan's DC40 |
Sunday, July 19, 2020
Knack Story -- Tom WX2J
RTTY Model 15 |
Friday, April 17, 2020
Walter's VFO
Main VFO board under plastic -- buffer board off to the right |
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.
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.
Wednesday, January 16, 2019
National Dial and Gearbox Problem Resolved
Pete was right -- the problem was really with the variable capacitor. The one I was using was kind of stiff and irregular in its motion. I found another one in the junk box that was easier to turn (it has one set of ball bearings). This fixed most of the problem.
I also spent more time making sure the shaft of the cap lined up perfectly with the shaft of the gear box. This also helped a lot.
I realize now that some of the "stickiness" that I occasionally feel while tuning may be coming from the dial -- not from the gear box. It looks like my dial took a hit that slightly bent one portion of it. It seems that the numbers have a bit of trouble clicking over on that portion of the dial. Some lubricant may help there. But I can live with it.
The receiver now tunes very smoothly and I can go right back to a frequency and find the signal exactly where I left it. There does seem to be a very slight difference depending on whether I "approach from above" or "approach from below" -- but this is not a big deal.
Check out the pictures of the receiver and the VFO. Note the "cardboard from a coat hanger" coil form. The winding is held in place with nail polish varnish. I had planned on having the variable cap, the coil , and the associated fixed caps all in a box for better thermal stability, but the VFO is very stable even without the box. I have the VFO running 455 kc ABOVE the signal frequency. It runs from about 7455 kc to about 7800 kc. I could have set it up to run 455 kc BELOW the signal freq. That would have made it a bit more stable (it is easier to attain VFO stability at lower frequencies) but VFO is so stable that I probably won't mess with it. I followed DeMaw's rules: Physical stability, NP0 caps. For the NP0 caps, put several of them in parallel to get the desired capacitance value. Keep heat-producing active components away from the coils and caps.
Thanks again to Armand WA1UQO for giving me this amazing piece of radio history. And thanks to Tim Sutton for the big box that holds this receiver.
James Millen knew what he was doing. See: http://www.isquare.com/millen/millen-page.htm
Wednesday, November 14, 2018
W7ZOI: Direct Conversion Receivers -- Some Amateur Radio History
http://w7zoi.net/dcrx68.pdf
Farhan and Pete WB9FLW alerted me to this wonderful article by Wes Hayward, W7ZOI. I guess my interest in DC receivers must have been noticed by the Google algorithm because I am bombarded by ads extolling the virtues of "Zero IF." Hey Google -- I'm already a believer! I was converted by W7ZOI's 1968 article in QST. And my belief in the technique has been greatly reinforced by his November 2018 50th anniversary article.
There is so much good stuff in Wes's look-back piece. The travails of trying to write for QST are presented very well. And we learn that none-other-than Doug DeMaw himself is responsible for the use of the word "presence" in describing amateur radio audio.
This article has inspired me to take a new look at the DC receiver I built last winter. Mine needs some work. I think it is kind of deaf. It could probably benefit from a diode ring detector. But it already has presence.
http://w7zoi.net/dcrx68.pdf
Thanks Wes. And thanks to Farhan and Pete for the heads up.
Sunday, October 7, 2018
Stockpiling Parts for Analog Oscillator STABILITY
Monday, January 1, 2018
Jeff Damm WA7MLH on QSO Today
Happy New Year!
There was so much wisdom and tribal knowledge in Eric Guth's interview with Jeff Damm WA7MLH. It was almost overwhelming.
https://www.qsotoday.com/podcasts/WA7MLH
My notes:
-- I sympathize with Jeff's decision to go solid state and give up on high voltage after an encounter with an undischarged 600 volt capacitor.
-- I really like the 1700 kHz IF with a 5 MHz VFO for an 80 and 40 meter receiver.
-- Interesting that EE degree didn't help much in his efforts to understand ham gear. Better to read Wes's books and Doug's.
-- Tek Spectrum Analyzers were specially made to fit down a submarine hatch.
-- Building and measuring just as important as studying the theory. Inked-up text books.
-- Learned ugly from Wes as a teenager.
--Searched for old commercial gear to gut and use as homes for homebrew solid state gear. The enclosures, panels and controls are very useful. Great way to avoid metal work. These rigs are no longer boatanchors! Again, I sympathize. I've sacrificed many Heath Lunchboxes and QF-1s.
-- Jeff Builds the VFO first. My preference too. But he understands Pete's AF-first approach.
-- Finger on the input of the AF amp! Buzz! Yea! Step your way back to the front end.
-- ALWAYS one stage at a time.
-- Osh Park Boards for standard circuit modules. Like Legos.
-- Cubic Feet of air variables. Jeff has a lifetime stash.
--Thinking about what was and should have been his section of EMRFD. Go for it Jeff. PLEASE!
-- Hesistant about chips. Analog guy. Would have been a huge time sink. Analog guy.
-- Buying parts on e-bay. Fewer and fewer RF parts at hamfests.
-- People reading QST Tech Articles for entertainment. Editor apprach: "Nobody will build it anyway." Handbooks giving priority to entertainment and less to information and education.
Saturday, July 15, 2017
Dino's FB W1FB Crystal Tester
Bill -
Enjoyed seeing someone else who has built Doug’s crystal tester on the blog. Here’s mine, built this back in early 2007. Anyone who wants to duplicate the tester can find the article in the January 1990 issue of QST or the updated article in the W1FB Design Notebook (page 192). Note that the QST article has a missing component value and a missing component (both corrected in the Design Notebook):
Saturday, July 1, 2017
G7WKE's Crystal Tester
Monday, January 23, 2017
Fifteen Back Iissues of "Hambrew Magazine" (from the 1990s) Available Online
http://www.arrowantennas.com/sub/hambrew.html
Sunday, September 4, 2016
First Signals from the "Armand HROish" Receiver
Saturday, May 21, 2016
SolderSmoke Podcast 187: 2nd Anniversary N6QW. Dayton. Bench Reports. Mailbag
SolderSmoke Podcast #187 is available:
http://soldersmoke.com/soldersmoke187.mp3
Second Anniversary of Pete Juliano's arrival on the SolderSmoke Podcast.
Dayton and FDIM underway
Bench Reports:
Pete:
-- Repurposing old Circuitry
-- Pete's small Display
-- New Transmitter
-- LBS in Japan and at Dayton
Bill:
-- S38-E The lipstick has worn off.
-- Reduction drive for the Mighty Midget's Mate
-- Back to the Barbados Barebones Receiver:
Which LO to use for 40 Meters with a 5 MHz IF?
Sideband Inversion and "Lower Sideband" filters.
Eradicating WWV with parts from AA1TJ
Improving VFO stability
A bandspread/bandset arrangement with fixed caps
Soul in the Old Machine
"The Amateur is FRIENDLY..."
MAILBAG