Straight Key Night M.O.P.A. Transmitter SKN Operating Position After reading a lot of ancient QSTs, ARRL and Jones Handbooks plus e-mail conversations with my friend, Louis VE3AWA about American depression-era style rig design, I decided to build a classic breadboard transmitter in time for Straight Key Night. Well, breadboard MOPA seemed like a very interesting idea, it was absolutely unusual for me - I never used wooden chassis (breadboard) without any metal shielding before. Second problem - Id started this project too late, for only one week before the SKN. To my surprise, I got my firefly finished and fired-up during Straight Key Night! Without any success - there was no SKN participants over here. But what done is done and I was so glad to hear many loud and clear signal reports and heartwarming words from EU CW stations. Maybe next SKN, VE and W stations will make a sked to work UU1CC. DESCRIPTION The complete circuit diagram is shown below. It is nothing special - choke loaded triode crystal oscillator and neutralised power amplifier. The antenna tuning circuit is arranged for the low-impedance loading such as Marconi antenna or coaxial (twisted line) feeding dipole. Slightly less common point of this design is a bias step-by-step keying circuit from the old Soviet handbook. Yes, i assume that such solution (especially germanium diode usage) is not so stylish for the golden-era wooden MOPA, but signal quality has a vital importance in my case - i planned to try this QRP baby with the powerful tube amplifier on the our local club station sometime. So, how does this keying method work and why I chose one as a best signal improvement? QRX, Ill trying to translate the handbook article... Lets go: The differential keying circuit is shown on blah-blah... At the moment of the key pressing capacitor C1 (0.25uF) quickly discharging through diode VD1 and resistor R2 (1k), thenceforth crystal oscillator starts to oscillate. Hereafter capacitor C2 (0.03uF) slowly discharging via the R3 (100k) and amplifier stage opens. At the other hand, when key unpressed, capacitor C2 (0.03uF) charging through the same resistor (100k), but C1 (0.25uF, much more than C2) - via high resistance of the R4 (100k). Thats why oscillator starts before and stops after the amplifier. Is it clear? Im not quite sure - too complex for understanding even without my terrific translation. Making long story short, this magic circuit provide same start-stop timings for the amplifier, but different ones for the oscillator. As a result - no chirps, no clicks at the ether and very smooth keying. PARTS I used common vintage parts from the 1940s up to the 1955, in particular resistors, paper and mica condensers, tubes. These tubes are Soviet analogs of the same RCA ones - native 6L6 has been replaced with the 6n3 tube from the 1942 (can be replaced with the more contemporary types such as 6n3c, 6n3c-EB etc.), in the triode oscillator stage i used 6c2c (analog of the 6J5-GT, best choice) and my lovely beauty 6c5c (analog of the 6C5-GT, pretty tube, but has slightly less output). Just for fun - I played with the Magic Eye Tube in the oscillator circuit - so pretty outlook, but very low level of the oscillation. As a XTAL I used several ancient Soviet rocks from the aircraft-mobile military VHF radio called RSIU - these crystals has been used in that station for the fast frequency switching. Exactly, i used only 7Mc native RSIU rocks, for the 3.5Mc band I made replacements using RSIU brown tubes (c) VE3AWA terminology) and penned tiny modern crystals. In the keying circuit I used vintage germanium diode D7 - such diodes has been used in the rectifiers of the old Soviet radios and TV-sets in the early 1950s. There are many types of diodes can be used in this circuit - from the modern silicon rectifier-type diodes up to the ancient selenium plates. Well, read the entire part list below: Name Value Description R1 9k1 1W R2 1k 0.5W R3 100k 0.5W R4 100k 0.5W R5 47k 0.5W R6 33k 0.5W C1 0.25 Paper 200V C2 0.03 Paper 200V C3 6800 Mica 500V C4 6800 Mica 500V C5 220 Mica 500V C6 1-15 Ceramic or air-spaced trimmer C7 2x300 Twin sections in series, rotor not connected V1 6J5, 6C5(GT) Analogs 6c2c and 6c5c V2 6L6 Analog 6n3 has been used VD1 D7 Vintage germanium rectifier diode Q1 7Mc, 3.5Mc FT-243 (nearly the same xUSSR rocks has been used) L1 Choke RF Choke L2 - See below L3 - See below Winding the coil on the non-pill bottle I placed in the separate chapter for several reasons. ALCOCOIL™ First of all, this bootleggers style in the coil-winding art has a great importance for the Depression-era MOPA builders. With little spare cash Novice HAMs had to use some unusual parts (such as fathers bottles or moms hair rollers) for the coil winding. On the other hand, there was much more dry bottles than hair rollers everywhere, on any attic because the Eighteenth Amendment. Mareira Wine Coil FormsSecond reason is obvious: I like the Madeira wine - its not my main hobby, but I like it, thrust me. Who does not love wine, wife and song, will be a fool for his lifelong! I would like to add the Morse code to this great assertion, but rhyme becomes really ugly. And at very last: Putting the fire back in firebottles - this is our slogan, isnt it? But who said that Madeira bottle cant become a Firebottle once upon a time? Souvenir wine bottle 1 7/16 inch. diameter has been used as a coil form. The ends of winding (including center tap) tied using a thin strip of cardboard as shown on the animated image. It is common solution for winding on slippery surfaces, such method ensures strong fixation without drilling holes. Winding the alco-coil For 80 meter operation the coil has 32 turns close-wound enameled wire, winding space occupies 7/8 inch. long. Same coil should be tuned to 40 meter using variable capacitor C7 - I successfully did it before, but I plan to make another (less inductive) coil for the 80-30 meter coverage in the nearest future. Antenna coil wound over center part of the plate coil and has 2 turns of strong enameled wire. CONSTRUCTION The SKN MOPA transmitter has been mounted on a dry varnished beech board 5 1/2 in. x 11 in. The arrangement of the various parts is shown on the following photographs. The keying circuit completely mounted on the small Bakelite board, bias resistors R5 and R6 soldered between this board ant tube sockets. As I mentioned before and as shown on the photograph below, rotor of the plate capacitor not connected at all - only stator blades has been soldered. One stator soldered to the tubes plate and the end of the coil winding, second one soldered to the another end of the coil and neutralizing condenser C6. A wooden cylinders was screwed at the corners on the underside of the baseboard, so as to elevate it from the table top to permit mounting the bypass capacitors C3 and C4 (6800). The various montage wires has been placed also under the board. I have a small amount of the rubber cotton covered varnished wires (remained from the military surplus antenna), so Id used these good-looking wires in the my MOPA for more ancient outlook. OPERATION What can I say? It is really plugnplay device - just plugging the XTAL and come on. Measured power was 17 watts on 80 meter band, slightly less (14 watts) on the 40m. Power output depends on crystal activity and triode used in the oscillator - when I played with The Magic Eye Tube, I got 5 watts on the 80m band at all. During the Straight Key Night 1 January 2008 I fired up this transmitter at the 40m band using the Long Wire antenna 270 feet long, but 25 high only. Here is my New Year roster below: CallSign UTC Sent Rcvd Comments SV1DPI 01.26 599 599 Kostas UA9MBR 01.30 599 579 Sergey, Omsk UA4IW 01.39 599 599 Vasiliy, Samara UR5THM 01.58 599 599 Sergey SM5BVF 02.28 589 579 Henry, nr. Stockholm UA4LF 03.30 579 559 Vladimir, Ulyanovsk, Homebrew DL4VM/QRP 03.50 589 589 Tom, Saar, 5W DK1KH 03.53 599 599 Klaus, Munich SV1DOI 04.02 589 559 Sotos, Piraeus UA3CS 04.09 599 599 Sergey, Pushkino UK8IZ 04.29 599 599 Yury, Samarkand OK1US 04.57 599 599 Jiri, Budijovice, Straight Key DL1NKS 05.05 589 599 Stefan, nr. Frankfurt F9KP 06.00 599 599 Paul, Ply As I said before, I use several rocks on the 80, 40 and 30 meter bands. Here they are: 3512, 3561.5, 7010, 7032, 7051, 7055, 10122.2 kc. My preferable frequencies are 7051 kc and 10122.2 kc, near the SKCC frequency 7054.5 I use my 100W tube amplifier. Check these points time to time and who knows? ATTENTION! These simple rules (TNX to Steve WD8DAS) can help You stay alive: Lay out the circuit so live conductors do not extend beyond the edge of the breadboard. Use insulated wire and spaghetti tubing to minimize points with exposed voltage. Dont work on the equipment when tired or angry. Turn off the power supply EVERY time a circuit change is needed. Turn off and unplug the power supply if the equipment is to be left unattended. Keep children, pets, Section Managers, and other simple folk clear of the energized rig. When testing and adjusting the operating transmitter keep one hand in a pocket. NEVER TOUCH C7 IN TIME OF TUNING! - It is stunning in place of tuning! Related articles by Zemanta Evergreen Exciter for the Special Night (timelesson.blogspot) More 1934 Transmitter (w0vlz.blogspot) Reblog this post [with Zemanta] Tags: breadboard projects , DIY Radio , Glowbugs , HOMEBREW , mopa , qrp transmitter , SKN , Straight Key Night , transmitter circuit , UU1CC PROJECTS Email This BlogThis! Share to Twitter Share to Facebook 5 comments : Anonymous said... Very very nice! Ill listen for your signals. 73 Ric K5RIX January 2, 2011 at 7:46 PM Anonymous said... Andy, Wonderful web pages. Lat year, I made a 6J5/6L6 MOPA from your schematic. Uses two metal tubes so it is glow-less. But it does have the retro look. Your passive differential keying circuit works like a charm. TNX es &# Chas W9SAY SKCC 1158T July 17, 2011 at 1:55 AM Andy UU1CC said... Its so pleasure to read it, Chas! And Im very interested to look a photo - if you have one, please send it to ur3ijc (at) gmail (dot) com. Hope to meet you one Straight Key Night on this radio. 73 Andy UU1CC SKCC 3072C July 17, 2011 at 5:13 AM David Newkirk said... Great work, Andy. Ill be mentioning the page and your page about the 6E5 variant in my Boosted Pierce page at mysite.verizon.net/dpnewkirk/ej/boosted_pierce/. A question: Whats the performance difference with and without neutralization? Neutralizing a Boosted Pierce final is something Ive considered for some time in the hope of cutting down reaction from final plate tuning and decreasing the RF level at the crystal. Best regards, Dave amateur radio W9VES mysite.verizon.net/dpnewkirk/ej/ July 25, 2011 at 12:24 AM Andy UU1CC said... Hello David. I just mailed an answer, but in short: I have a big problems with high RF level on crystal and crystal overheating on 30m band. Now I think that main mistake was to use a tiny modern quartz on this band. Anyway, neutralization solved this problem completely. 73! de UU1CC August 17, 2011 at 8:17 AM Post a Comment Newer Post Home Subscribe to: Post Comments ( Atom ) Hammarlund Meter What is Glowbugs? 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To browse visit here. © Old Black Telephone Popular Posts Straight Key Night M.O.P.A. Transmitter After reading a lot of ancient QSTs , ARRL and Jones Handbooks plus e-mail conversations with my friend, Louis VE3AWA about American de... 6N7 Tube QRP Power Amplifier - One Rainy Day DIY Project Once upon a time Id decided to join a Big Guns Gang and made a Super-Duper Powerful Vacuum Tube QRP amplifier for my 800mW QRPP h... Evergreen Exciter for the Special Night Several days ago I listened to the completely empty ten meters band. There was a lot of noises, quiet CB chewing and nothing else. Sudden... © UU1CC. Powered by Blogger.
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