Happy New Year to all. May you make good progress on your homebrew projects, and may the radio gods act favorably on your behalf.
73 es HNY de N2CQR
Serving the worldwide community of radio-electronic homebrewers. Providing blog support to the SolderSmoke podcast: http://soldersmoke.com
Happy New Year to all. May you make good progress on your homebrew projects, and may the radio gods act favorably on your behalf.
73 es HNY de N2CQR
-- April 27, 1973. Novice Ticket becomes effective. WN2QHL. Age 14.
-- July 19, 1973. First contact (with Elmer WN2NEC). Age 14.
-- February 1 and 2 1973. A grumpy old-timer calls -- during the Novice Roundup! -- to tell me that I'm putting harmonics onto the 20 meter band. I get scared and go off the air. Geez! I probably just needed to retune the tank circuit. Age 15.
-- February 23, 1974. I go back on the air with a DX-100. Age 15.
-- March 5, 1974. I take the General Class exam at the FCC office in New York City. I pass. Age 15.
-- April 11, 1974. I buy the Drake 2-B from WN2NEC. This revolutionizes my radio life. Fifteen meter contacts become possible. Age 15.
-- April 13, 1974. I work ZL2ACP on 15 meter CW. I wake up my parents to tell them. Age 15.
-- April 21, 1974. END OF NOVICE OPERATION. Apparently we were still working under a one year limitation on Novice operation. Could the expiration date have been marked on the license?
At this point the FCC screwed up and sent me a Technician License instead of a General Class License. My father got on the phone to Gettysburg and straightened this out. Thanks Dad. So I was only a Technician for a few weeks.
-- April 9, 1974. General Class License effective. I become WB2QHL, a man of substance. Age 15.
-- May-June 1974. I acquire a Heathkit HW-32A 20 meter SSB transceiver from the Crystal Radio Club. But I have to build the power supply from an old TV. Somehow, I survive. Age 15.
-- June 11, 1974. First contact with the HW-32A. Age 15.
-- November 9, 1974. Last contact with the HW-32A . Age 16.
-- March 15, 1975. First contact with my Hallicrafters HT-37. Age 16.
This has been one of the major complaints about our beloved analog LC VFOs: The frequency tuning on these circuits is often not linear. For given amount of VFO frequency dial turn you can get vastly different changes in frequency. At one end of the tuning range the frequencies are nicely spaced and tuning is easy. But at the other end of the tuning range all of the frequencies are bunched together. This is one of the problems that leads some homebrewers to defect to the sad land of "digital VFOs."
But wait. It appears that the old designers found a solution to this problem. Just look at the tuning dial of my HT-37. The frequencies are all spaced out evenly. How did they do that?
I had been thinking that this success may have resulted from Hallicrafters' engineers using the series-tuned Clapp circuit. Here the main frequency determining element is a series-tuned LC circuit and not the parallel tuned LC circuit that we see in the more commonly used Colpitts circuit.
But hold on -- how could that be? The frequency bunching problem that we attributed to the Colpitts circuit must also exist in the Clapp, right? I went back to SSDRA where there was a good discussion of Colpitts and Clapp VFOs. The advantage of the Clapp was said to be in its use of a larger value coil which helped minimize the effects of stray inductances. But there was no mention of the Clapp offering improved linearity in tuning.
I have in front of me two transceivers: The Mythbuster uses a 9 MHz Clapp circuit (see below). The 17-12 rig uses a Colpitts Circuit. I checked the tuning linearity of both. Both appeared quite linear in tuning, with no real difference between the two.
Then I looked at the tuning capacitor in the Mythbuster 17-12 rig. It came out of an old Hallicrafters transmitter, probably the HT-44. I looked closely at the stator and the rotor plates. Both are curved. I'm guessing that this may yield a more constant change in capacitance for a given movement of the main tuning dial.
Next I opened up the VFO on the Mythbuster. (It is the VFO from an old Yaesu FT-101.) I couldn't see the stators very well but it appears that their shape is different from the square shape we often see in variable capacitors. Could it be that this variable capacitor was also made to provide linear tuning?
Back in 2013 Norm Johnson wrote about all this in the Antique Radios.com forum:
A capacitor that has uniform increase in capacitance with rotation will have the stations at the high end of the band squeezed together. Another type known as the straight-line frequency variable capacitor has, as you might guess, a characteristic that gives even spacing of frequencies with shaft rotation. These were popular in the 1920's but weren't very good for superhets where you needed to have a dual section capacitor that would tune both the RF and local oscillator, and have them track each other properly. The midline variable capacitor is more compatible with a superhet, and easier to make both sections track properly. This is the type that you see in most receivers from the late 1930's to the end of the tube era. They don't have quite the equal spacing between stations across the band that the old straight-line frequency caps had, but they're much better than the variables that change capacitance linearly with rotation.
I wrote an online calculator that helps in the design of the tuning. It shows what frequency range you'll get with a specific type of variable capacitor, including the effects of padder and trimmer capacitors. It also displays a dial scale that shows how the frequencies are lined up accross the dial.
http://electronbunker.ca/eb/BandspreadCalc.html
Steve W6SSP also provided some really good info back in 2013:
There are three types of open, variable plate caps;
SLC= straight line capacitance where the capacitance varies linearly,
these are the most common and have half-circle plates
SLF= straight line frequency where the plates are tapered to allow
for linear tuning of the frequency
SLW= straight line wavelength, you get the idea...
SLF and SLW caps have oblong plates.
The effect on tuning a receiver can be dramatic. One example is the
Hammarlund SP series of receivers where the ham bands are very
compressed at one end of the tuning range. They used SLC caps
in the VFO. On the other hand rigs like the Kenwood TS-520
and FT-101 series have linear tuning across each band. These use
SLF variable caps. Most old 1920's battery radios used SLW
where stations were identified by their wavelength.
Steve W6SSP
I looked at the tuning dials on my Hammarlund HQ-100 receiver. It is fairly linear in its tuning, but not as linear as the HT-37 or the Drake 2-B; on all of the tuning ranges the frequencies seem to spread out a bit at the lower end. My guess is that Hammarlund used the midline variable described above by Norm Johnson. The HQ-100 did use a ganged variable cap, with one section tuning the RF amplifier and the other tuning the local oscillator.
Second, this is a work in progress. That is why my diagram (below) is a bit ugly. I am looking for your input and advice on how I might do this better. I will understand if religious principles prevent some of you from participating in this endeavor.
I am trying to solid-state this device WITHOUT major surgery, and without adding any reactive components that would change the resonance or tuning range of the original. The original circuit tunes from 5 to 5.5 MHz and that is fine with me.
In Part II I'll show you how this thing sounds and what it is like to use it for SWL, CW, SSB and AM.
I heard about this video while trying to track down information on John Stanley Anderson's 1939 television receiver. "Patrolling the Ether" is kind of hard to find. It is not really on YouTube. But there is a good BARC Vimeo video about WWII RDF efforts that includes at the end the full "Patrolling the Ether" video.
Here it is:
Thanks to BARC and to Brian Harrison for putting this together.
In the video, they discuss the invention of the Panadaptor by Dr. Marcel Wallace F3HM during World War II. I set up a very crude Panadaptor using Wallace's principals:
https://soldersmoke.blogspot.com/2019/05/diy-waterfall-quick-and-easy-panadaptor.html
Rarely if ever will we come across a high quality NETFLIX series built around a shortwave broadcast transmitter. But that is what we have in Gloria. It is really good. We were especially interested in it because we lived in Portugal for three years. In addition to all the intrigue and drama you will catch glimpses of broadcast antennas, big transmitting tubes, and one out-of-focus shot of what appears to be a Hallicrafters receiver (SX-42?)
More info here:
Here's the NETFLIX link:
https://www.netflix.com/title/81073977
Thanks to Thomas K4SWL of SWLing Post for the heads up.
RTTY Model 15 |
Winterfest S-38E on the left, junker on the right |
Winterfest RX on the left, junker on the right |
Where I placed the isolation transformer on both my S-38Es |
Recapping in process. Hayseed electrolytic in green can.. Old tubular caps being replaced by new yellow caps. |
Recapping completed |
Broken Bandspread string from Winterfest S-38E |
Approximating the size for the replacement string |