Addding a Beat Frequency Oscillator (BFO) to a Domestic Receiver.

[Station X]

Here's the text originally posted by Adi in this thread about Regenerative Receivers:-

https://www.vintage-radio.net/forum/...ad.php?t=11746

However, the idea of adding an extra BFO to a normal domestic radio seems like a cool idea. Would i be able to pick up much amature ssb traffic with the frequancy range and controls of a domestic radio?

I think with one of these, a good ariel and maybe a simple untuned RF preamp between the radio and the ariel something good could be knocked up.

I really even more like the idea of using a ceramic resonator for the BFO. This will save on using any coils. And the circuit looks like something that can be knocked up easily in a few minuits and use power scavanged perhaps from the o.p valves cathode or rectified heater winding.

How woudl you go about connecting a BFO to a normal reciever?

Thanks.

[Biggles]

The easiest way is to have no connection at all. Make an oscillator with a frequency of the IF of the radio, preferable tuneable a few KHz either side of the IF. With a bit of luck with the oscillator placed near the radio, you will hear heterodyne whistles as you tune across the band. These whistles will appear when you receive a transmission. i.e. no radio station, no whistle.

If the radio is tuned to a SSB transmission, without a BFO on, the audio will sound muffled and unintelligible. With the BFO on, and tuned to the IF frequency, hopefully you will hear the audio become understandable as you tune across the transmission.

You will need to experiment with positioning of the BFO in relation to the radio, and also may need to vary the BFO frequency slightly around the IF frequency. This is a VERY simplistic explanation and I am not the best at describing things, but it may give you a starting point.

Ceramic resonators are generally not adjustable, so only use these on fixed oscillators. If the radio only tunes in fixed steps i.e. modern digital ones which say tune in 9KHz steps, then the BFO will have to be variable. With an old analogue continuously tuned radio, the BFO can be fixed in frequency.

Biggles.

[paulsherwin]

You can pick up many of the amateur bands with a normal domestic SW receiver covering the 19m-49m broadcast bands. The only trouble with this is it won't receive the 80m amateur band which is popular with UK amateurs. Radio amateur forum members might like to comment further on this.

You don't need to 'connect' a BFO to anything. It will radiate at the IF frequency so you just need to ensure the IF stage of the radio picks it up. With a transistor set it will probably be enough to put the BFO by the side of the radio. A valve set with a metal chassis may need an 'aerial' from the BFO running underneath the set, or even inside it if the bottom is well screened.

I wouldn't build it inside any particular radio. It's much more use if you power it from a single AA battery and try it with different radios.

If you build it using an IFT rather than a resonator it will be easier to adjust the beat frequency. Anything scavenged from an old transistor radio will do.

(Biggles beat me to it )

Paul

[Station X]

An SSB signal received without a BFO will sound like Donald Duck, but unintelligible.

Amateur Bands to try are 80 metres (3.5 to 3.8 MHz), and 40 metres (7 to 7.10 MHz). It was on a domestic radio that I first listened to Amateur Transmissions on 40 metres. In those days it was AM though.

Adi. I'm not sure whether your aim here is to construct a receiver, listen to Amateur Transmissions to see if you fancy getting a licence, or both. I can't help feeling though that you'd be better off begging, borrowing or buying a comms receiver. They often crop up on eBay at reasonable prices and you can look for something in your area to avoid postage charges. Look out for receivers such as the Yaesu FRG7, Trio/Kenwood R1000 and Trio 9R59DS. The last named was probably the last valve communications receiver ever made circa 1970.

[adibrook]

Thanks for that info.I am on a lookout for a comms reciever, and i see the use in it. But while i havnt found one yet, it would be cool to listen to some SSB transmissions on bodget up equipment.

So, as far as i understand it...if a normal AM radio recieves SSB, it will sound like donald duck on drugs. So the 1st thing i should do is tune my normal Ekco radio around the shortwave band to see if i hear anythgin that sounds like donald duck. Then if i do that means it picks up some amature traffic, and then i can build a BFO, and it will sound normal.
Is this correc so far?

[adibrook]

Umm...error

I just realised that my Ecko doesnt have SW....duh.

In fact i have no operational radios that tune to shortwave. My PYE suitecase radio and the Vidor portlable dont tune to SW, and i dont think the othe Ekco does (its the type with no actual tuning, just presets).

That leaves possibly that old Marconi 264, which is not even operational yet.

Thats wierd, i never thought about short wave untill now. It doesnt seem that common on old radios...

[paulsherwin]

Originally Posted by adibrook

Thats wierd, i never thought about short wave untill now. It doesnt seem that common on old radios...

Actually, SW *is* common on old radios Most 1940s and 50s woodies and large bakelites have SW, and they often perform quite well. Three wavebands seem to have been expected in radios sold as 'main' sets. With the introduction of FM sets started to lose SW replacing it with VHF.

2 wavebands were common on radios sold as second sets for use in kitchens, bedrooms etc. Most valve portables would fall into this category.

It's quite odd that you've finished up without a working SW broadcast receiver. Still, all the more reason to build that 1 valver being discussed in your other thread You can build a similar set using transistors: http://vintageradio.me.uk/radconnav/...%5Ccircuit.jpg

Paul

[Sideband]

At a pinch, if you can get a set that covers SW, you can just about get away with using another radio as a BFO. Believe it of not I actually managed to get some resolvable SSB by using my Philips tuner which has a SW band and covers the 7 and 14 MHz bands. This was in the days before I had a proper comms receiver and I had re-kindled my interest in amateur SW listening.

Using my tuner set to SW I tuned in an SSB transmission around 7MHz and then tuned another radio to 'beat' with the IF of the tuner. I managed to hear quite a number of amateurs this way. Of course this method is very crude and is not very stable but it DOES work. The advantage was that it was zero cost and took about five minutes to set up. I never expected it to work at all and was completely surprised by the results.


Rich.

[jim_beacon]

The level of injection for teh BFO is reasonably critical - different levels give optimum results for CW and SSB (I forget which need more). The usual way was to take the output of the add-on BFO to a piece of coax, with the end un-connected, and stripped of braid for a short length. The bare end is then placed near the final IF transformer, so that the BFO is capacitivly coupled to the last IF stage.

There were a number of articles published about this in the 50s and 60s, including simple one transistor add-on BFO circuits.

As regards recievers, the attache portables were popular for top-band (160m) portable reception, and can be easily retuned to cover the band.

Jim.

[wireless_paul]

Originally Posted by jim_beacon

The level of injection for teh BFO is reasonably critical - different levels give optimum results for CW and SSB (I forget which need more). The usual way was to take the output of the add-on BFO to a piece of coax, with the end un-connected, and stripped of braid for a short length. The bare end is then placed near the final IF transformer, so that the BFO is capacitivly coupled to the last IF stage.

There were a number of articles published about this in the 50s and 60s, including simple one transistor add-on BFO circuits.

As regards recievers, the attache portables were popular for top-band (160m) portable reception, and can be easily retuned to cover the band.

Jim.

It was the standard Japanese transistor radio that got me started as a SWL. Some of these went down to top band without any adjustments being made. When I first heard hams I would not have known what they were, luckily my father’s colleague was a Radio Amateur! Of course this was in the good old AM days. That would be about 40 years ago.
Paul