Help for the BFO-LESS

Yes you can build a Beat Frequency Oscillator for your deprived radio. This little circuit uses common parts and tunes to handle any BFO need from 400 to 500 kHz.

[@ssboot5663]

WOW!! Just WOW! I wish I was younger and smart enough to learn and retain all of this stuff!But unfortunately I'm now older (senior citizen)and missed my early boat with no real access to the information and education in the years that would have put me on track in electronics,and l had short attention problems throughout my life so Now days I know mostly the simple basics of electronics and its capabilities and not much more..! But I'm still learning as I watch your videos, keep up the good work! I have always LOVED electronic stuff, especially radios!

[@MIKROWAVE1]

Sometimes I break more than I fix. Thanks for watching!

[@W1RMD]

@@MIKROWAVE1 breaking stuff is the best way to get more in your parts bin!

[@UpcomingJedi]

You still can. Libraries still exist and being older, youre sure to have more free time to pick up the hobby.

[@W1RMD]

Great videos! This channel is a gold mine. Thanks for sharing this knowledge with us. Great delivery of content and editing as well.

[@AuroraMills]

Thanks for sharing your encyclopedic knowledge with us Mike!

[@milanstajic3294]

BRAVOOO majstore. Profesore. Odlicno objasnjeno 73 iz Srbije sve najbolje.Milan..

[@n8nkqrp595]

Dear Sir: You are the master of the crystal (Galena and cat's whisker?), the loop and the condenser! Quite possibly the aether as well. You exploit, to great advantage, 'spooky action at a distance'. Oops, wrong guy. But whatever. You follow in the footsteps of Maxwell, Faraday, and Tesla. Thank you Mike for your AMAZING vid work. The forethought, setup, carefully planned out - yet unscripted, friendly and VERY intelligent work is amazing. Merry Christmas to you and your family and a sincere '72 & 73 OM' from the great state of Michigan

[@caulktel]

Wow! Great video at just the right time, I have been researching BFO’s for the last week to add to some of my boat anchor receivers, thanks!

[@Derrick6162]

Instructions very well done. Thank you.

[@berndb.5097]

That was really an excelent explanation. The same thing I did in my early years on my old AM - CB radios. mny 73 Bernd

[@MIKROWAVE1]

Yes that is a classic application to copy SSB!

[@hwatson069]

I have watched several of your videos and really enjoy them! Keep up the good work Happy Holidays AB9UB

[@Yarz01]

Thank you so much for this video now I can upgrade some of my old receivers.

[@PapasDino]

Nice job Mike...filed that circuit away in my reference binder. Happy Holidays! 73 - Dino KL0S

[@daviddavidson1372]

Great video as always. Gonna build this and waite for part 2

[@acestudioscouk-Ace-G0ACE]

This was great, as a beginner the explanation and talk through centre tap coils was really good.

[@MIKROWAVE1]

Thanks for watching!

[@Homer19521]

Your vid was very helpful. I built a couple of BFO's but I did not understand how they could overload & desense the receiver. Now I know! Thanx.

[@MIKROWAVE1]

Great work! Building BFO's and even Q Multipliers for various IF frequencies is a lot of fun. Using a proper (separate) product detector goes a long way in reducing the tendency for self interference. But dribbling in some BFO is sure better than no BFO at all!

[@wansolve2036]

You'd think that someone who'd complain that the junk box parts you selected as "too old" would have the wherewithal to grasp the concept and simply select newer style coils or just wind their own. Thank you for putting this together, great videos!

[@MIKROWAVE1]

They are all jealous of a righteous junkbox!

[@vinceotten129]

Thank you for a very helpful video!

[@MIKROWAVE1]

Thanks Vince. I hope you build a BFO.

[@catman351]

Love the intro.

[@mostlypostie1]

Great video! thanks!

[@SpinStar1956]

Great video Mike! Years ago, I had to purchase a wideband RX and could only afford the IC-100. I always hated the fact that they went to the trouble to make it that wideband but cheap'd out on the modes. Anyway, I may give this a try. I have some super-small IF cans that I bought as a bulk-bag and I regularly do SMD projects so would like to get it into the original cabinet (maybe with a varactor or something with controls on the back. Anyway, really enjoyed the video! 73...

[@MIKROWAVE1]

Yup just a "monitoring" receiver.

[@area46241]

Fantastic!

[@TerryMcKean]

Thanks for sharing, MIKROWAVE1 The concept of getting a BFO going reminds me of years ago when I built from scratch, using tubes and sockets etc etc etc from junk TV chassis and other stuff, a transmitter/receiver rig for 40 meters.* The BFO effect for that rig's rx section was attained by wrapping one end of a length of insulated hookup wire (insulation and all) a couple turns around the wire going from the primary terminal of the first IF transformer to the plate connection on the 6BE6 converter's socket and the other end of the insulated hookup wire a couple turns around the wire going from the secondary of the second IF transformer to the diode connection of the 6AV6 detector/af amp's socket, thus establishing a 'gimmick' capacitive coupling at just the right phase between the input and output of the 6BA6 IF stage and causing the IF stage to go into self-oscillation at a 455 KC rate and that made a simple effective way to hear SSB and CW signals. To control the amount of IF regeneration I put a ten-turn 2 watt 100 k potentiometer in line with the screen grid voltage to the 6BA6 IF amp. By adjusting that pot made very smooth gradual transition at that sweet spot from 'no-oscillate' to 'oscillate' and served very well at bringing up the sensitivity and selectivity for copying the AM signals. * The rx section of my 40 meter homebrew rig had a 6BA6 RF amp, 6BE6 convertor, 6BA6 regenerative IF, 6AV6 detector/af amp and a 6AQ5 af out. The tx side had a 6AG7 xtal oscillator** and a 6146 rf out, and ran about 50 watts input on CW and about 30 watts input on AM fone. The AM modulator section consisted of a 12AX7 mic amp/af pre-amp, a 12AU7 af amp/phase inverter, then a pair of 6DQ6's in push-pull for modulator-output and that circuitry tickled the plate and screen voltage feed going to the 6164 rf out at an audio rate. :-) All that circuitry along with the power supply was built into a single 12 inch by 12 inch by 12 inch metal cabinet. **The 6AG7 xtal osc also served as a buffer when I used an external VFO.

[@TerryMcKean]

The external VFO was a junked Heathkit VF-1 which I redid and simplified into a single-band 40 meter VFO. After I got done with re-doing it it's 6AU6 oscillated in the 160 meter range and the output coil multiplied that a couple times so it outputted a 7 mc carrier. Eventually I found a 1 inch CRT and built that into a 40 meter modulation monitor and power supply in it's own little cabinet, and another time I found a roller-inductor and built that along with a couple of variable capacitors into an antenna tuner in it's own cabinet. My whole station back then was this homebrew stuff. That was back in the 1980s and 90s when I lived in Phila PA and had the call of N3HJQ. I also had a Gonset GSB 100 tx and a National NC-300 rx and a Clegg 99'er and some other cool commercial-made vintage ham radio gear, including a Johnson Invader 2000 tx... that Johnson tx was friggin' awesome... lol :-D My HJQ call eventually expired in 2002 as I got so busy and involved with my work and I forgot to mail in the fees to keep that HJQ call going. "N3HJQ" has since been reassigned. Eventually I'll find a VEC somewhere here around Big Sur Calif and retake the tests and get another call and get back on the air. :-)

[@TerryMcKean]

Back when I had the E.F. Johnson Invader 2000 I experimented with that 'mitter in the effort to get the best-sounding AM out of it, which was eventually attained by totally bypassing the SSB filter by disconnecting the input and output leads to the SSB filter box and bridging the new gap with a .01 mfd ceramic capacitor, and increasing the microphone input resistor to 10 megs and fattening up the coupling caps in the microphone amp , and using an un-amplified D-104 microphone. The mods opened up both side-bands in AM and increased the frequency response and it sounded very good ... in fact, I was QSO'ing with Tim WA1HLR through the Invader 2K tx and NC-300 rx after doing that mod to the Invader 2K and he said it sounded excellent... " ...the best I ever heard from you..." he added. It got the "Official TimTron Seal Of Approval" ;-)

[@user-ig8ov4sp3n]

WOW WOW!!!!I LOVE YOU

[@MrBugsier5]

Works nice!

[@vacuumfireradio253]

Great stuff Michael. Another excellent presentation. If you're in the mood for another project would you consider building and explaining the theory of a simple crystal filter and phasing control such as used on the HRO? It would segue nicely from this presentation. You could possibly then move to more complex multi pole filters possibly.

[@markjacobsen302]

Nice vid Mike. I don't usually comment but this time I just had to. I built a 455 KHz bfo sort of like this one except I used the yellow transformer with a MPF102 and I tuned it with two LEDs connected back to back used as varicap diodes. They provided just enough junction capacitance to swing the bfo about +/- 4 KHz

[@MIKROWAVE1]

Awesome! Excellent idea on the LEDs. I will be starting the ceramic resonator work soon. It takes more C to move them!

[@kf5hcr176]

@@MIKROWAVE1 I'm sure you know this, incident light may affect LED properties

[@hwatson069]

A few years ago, I built a 455 kHz resonator oscillator. If memory serves, it was of the Colpitts type with a (Yellow?) IF transformer as a drain load and output coupling. As I recall, I was able to pull the oscillator plus or minus 3kHz without difficulty...using a variable capacitor. Oh, I think I used a N-Channel JFET 2N5245 or similar. I was thinking of adding a varactor in place of the tuning capacitor; I didn't get there yet.

[@stephenwilliams5201]

Tks my RadioShack radio Is w/o so it's good to see. Tks

[@vidasvv]

Great explanation, TNX 4 the upload! 73 N8AUM

[@zbyszekpodchmielony2642]

Your BFO is working Ok! maybe add filters for SSB and CW to this receiver :-) Thank you for the interesting video Best wishes from SP7GXK

[@RobR386]

Nice and simple, working great :-) 73 M7PDF

[@Gordonseries385]

Enjoyed your early presentation on BFOs didn't know they had bfo stations are you going to get into designing a product detector circuit to go with the bfo circuit?

[@mikesmuseum]

Can you use a varactor diode to vary the frequency (or the tuning ability) of a BFO? Would really like to see that implented. 👍 Great Video!

[@MIKROWAVE1]

I substituted the variable with a 12K feed resistor off a 50K pot with the 5V and a 200 pF cap to the same spot on the collector. For a varactor I used, a Motorola MV115, Red, Green and Amber LEDs, and a 1N4004 and 1N4007. Exercise: Put them in order of effectiveness in kHz per full swing of the pot. Any guesses?

[@TheGameBusterPL]

The most common kind of diodes with high change of capacitance ( delta c ) are zener diodes. 0.5W to 1W types work good. They change their capacitantes from 600pF to 200pF if I am correct, use zener voltages 1.5 times the tuning voltage. Look up "zener diode as varicap".

[@neilcampbell4833]

Could I use a bfo on a modern Sw radio with a DSP chip? Like on a radiwow ?

[@margaqrt]

Great video. I learned a lot. What component was used for the power level output adjust control? Just a potentiometer? Thanks, de KE0RFZ

[@MIKROWAVE1]

Yup, just a small 500 ohm or 1K pot is fine for RF at frequencies up to 10 MHz or so when you just need simple attenuation.

[@danedewaard8215]

Just wondering if this BFO could be used on a portable radio by inductively coupling to the whip antenna? I'm guessing that the output might need tweaking to reduce overload!? Thanks for this great walk through of BFO history, design and build.

[@MIKROWAVE1]

The BFO injection needs to be close to the last IF or the detector to be most effective. To force it through at the antenna through at least 2 tuned circuits and stages is going to require a lot of extra signal power.

[@danedewaard8215]

Ah hah, you say extra power!!! Thank you for that!

[@justinelliott3529]

What would happen if you didn’t use the capacitor

[@tubeDude48]

Here's a couple of BFO's I use: www.geojohn.org/Radios/MyRadios/S120/S120.html --- bgmicro.com carries these CANS.

[@loverofthelostnarc]

I wish I had Google in late seventies to the nineties, it would have been a great help for me to build a BFO. I have damage my father's transistorised Philips radio and it still lying with me. I cannot get those ferrite IF cores for it. They are all broken.

[@MIKROWAVE1]

Re-collect one. They are out there! There are some folks who try to relive their childhood by buying all of their favorite toys in adulthood.

[@GardenBushcrafter]

Could Q-Multiuplier work as BFO for this radio too?

[@MIKROWAVE1]

It might but you can not have it both ways. The Q multiplier works best before it goes into oscillation. And you would not put it at the end of the IF chain, you would want it at the first 455 can near that mixer.

[@GardenBushcrafter]

@@MIKROWAVE1 Thank you for your reply. Great videos as always, my favorite KZbin channel.

[@ku4uv]

Hope this isn't a stupid question, I am assuming the C1 capacitor 0.1microFarad, and all the rest are in picoFarad? Also, the R3 potentiometer is a linear pot?

[@MIKROWAVE1]

Yup on all 3 and excuse the shorthand!

[@carl112466]

Could you use a DDS and arduino

[@MIKROWAVE1]

Yes with a bit of shielding and filtering, but this old radio is pretty old for that kind of modern love!

[@stephenwilliams5201]

Ordered a Tentec bfo and inject it's out put to the if stage thrugh a cap for isolation. Scarry how it works

[@MIKROWAVE1]

Very Nice! And no shock!

[@stephenwilliams5201]

@@MIKROWAVE1 yes it works well with the Chinese cheppys. Though if it is analog or digital. You would have put up with the rigid tuning( digital)but works well for net stations recived usually in even numbers. Say net frequency Ie 7135,, 7.140. 7.150. ect so the rig is endowed with some good SSB EVEN THOUGH it wasn't designed. For such. Winner. Winner.

[@jackhreha4907]

Like the theroy review. Your parts are not that old, No dc tubes. So many raidos with no BFO'S Thanks Jack Hreha/

[@DAVIDGREGORYKERR]

That transceiver have have a way of switching to SSB mode possibly going through the menus. What about using a 74HC4066,74HC74 and 74HC00 at 455khz x2 for a SSB de-modulator i.e. lz3nf.wordpress.com/2013/07/25/280/

[@MIKROWAVE1]

Plenty of stuff on the net on the digital techniques. I used to be an applications engineer at ADI, so I shun the new stuff on my channel and try to keep it simpler.

[@MirlitronOne]

Very good, but please lose the bit about diodes detecting by rectification. You mix carrier (or beat frequency) with one or both sidebands in a non-linear mixer (diode), and you get sum and difference frequencies. The difference frequency IS the (detected) audio. No "envelope detection" theories needed.

[@MIKROWAVE1]

Interesting isn't it? Whether you describe is as a nonlinear mixer with the sum frequencies filtered out, an envelope detector by rectification, or simply as a negative peak clipper, the old fashioned crystal set still causes controversy.