The Ten-Tec Universal 455 khz BFO is a small project board that you solder together yourself to enable AM-only shortwave radios to tune single-sideband or CW. Instead of hearing thumps or donald-duck on the bands, you can now listen in to USB/LSB/CW. Your radio needs to use a 455 khz or so 2nd IF, as the kit beats a signal near that, and this is what allows for cw tones or ssb to be heard properly. It retails for around $11 U.S.
Ten-Tec mentions that it is for "casual" use, and they are right. In other words, it won't turn your AM-only Grundig S450DLX field radio into a cheap version of a Satellite 750. Yet hearing quality SSB or CW from any radio not specifically designed to receive it, is a load of fun, and worth the small time building the kit.
In fact, I used the Grundig S450DLX as a test for the Ten-Tec BFO.
There are just a few parts, and the instructions and board layout is pretty obvious. There isn't much too it other than just making sure that the parts go in the right holes, and the banding on the diodes face the right direction. The silkscreen on the board makes it obvious.
I powered it from a single 9V battery, but had to get the battery holder wire on my own. The output consists of just two small wires you supply, or you can use maybe thin coax if you intend to solder it down to a receiver's board permanently.
Ideally you should put this thing in a metal case, which Ten-Tec also has, or you can put it into an Altoids box, whatever your fancy. For my test setup, I just let it all hang out on the desk without an enclosure. I also had a spare knob lying around, which makes it easier when tweaking the BFO pot.
How do you hook it up?
It all depends, and you have to experiment. You need to get the output wire(s) at least close enough to the radio to allow for the beat, yet you don't want it so strong that the bfo signal just swamps the front end. Sometimes you hook up the negative output ground wire, and sometimes you can rely solely on the + output wire to just capacitive couple itself into the radio.
In the case of the Grundig, below 14 mhz, I was able to just place one of the output wires along the back of the plastic case. Above 14 mhz, I had to actually clip the + output wire to the base of the antenna itself. But with my sloppy on-desk layout, there are a number of ways a decent BFO signal could be accomplished.
How do you calibrate it?
There are only two adjustments on the board - a canned tuning slug, and a fine-tuning pot. Put the pot in the center of travel. Tune your receiver to 455 khz, and tune the slug for as close to zero-beat as you can.
OR, if your receiver doesn't tune down to 455 khz, no problem! Just tune to a frequency of interest, turn the can-slug until you hear the BFO-beat zip on past, and back it in to as close to zero-beat as you can - although no need to go nuts about it, as you'll be adjusting the pot next. Now you adjust the pot until you hear the SSB or CW clearly.
Note that for withing 3 - 30 mhz, I only had to travel somewhere though just one turn of the canned-slug to land on frequency with the bfo.
Why is this casual use?
First, if you tune off-frequency a few khz, you'll have to readjust the bfo pot. In my case, below 5 mhz, I had only about 15 khz or less overall play in the pot until it ran out of steam, requiring retuning of the can-slug. When it ran out of steam, I returned the pot to the central position, and then tuned the can-slug for close to zero beat - each major change of frequency required this two-step approach.
So zipping up and down the band below 5 mhz was a tedious experience. Great quality SSB/CW, but tedious nonetheless, and I did the "retune-the-slug-dance" for large excursions in frequency.
From about 7mhz to 22 mhz, things were better. The pot itself had more coverage, and on the amateur bands in between, I only had to retune the can-slug at the band edges. But, I noticed that the actual pot adjustment getting a little tighter to make sense out of ssb.
Above 22 mhz, I had large amounts of varactor pot coverage, and barely had to touch the can-slug at all, but man, I really had to concentrate when turning the pot in extremely fine increments. Do not drink coffee above 22 mhz.
So essentially, on this Grundig S450, on the low bands, I had to retune the can-slug quite a bit, followed by fine-tuning of the pot, but this fine-tuning wasn't so finicky. As I went higher in frequency, I obtained a lot of band coverage without having to tune the slug, but just breathing on the pot could make ssb unintelligable.
In the end, this was a lot of fun, and proved that the S450 is quite capable of ssb, and stable enough to follow a 30 minute qso with only very minor touch-ups of the bfo every 15 minutes or so. But the tedium of readjusting the slug for wide-frequency operation makes it just like Ten-Tec says: casual.
I suppose if you are a utility listener, and wanted to dedicate an AM-only receiver to some spot coverage of ssb, then you could go all the way and mount this kit inside it.
For what it is, this thing rocks - it is just so much fun to use. So what's next - hey I've got a little Grundig M400 buried in a travel bag! Let's see how THAT likes doing ssb/cw !!
Ten-Tec mentions that it is for "casual" use, and they are right. In other words, it won't turn your AM-only Grundig S450DLX field radio into a cheap version of a Satellite 750. Yet hearing quality SSB or CW from any radio not specifically designed to receive it, is a load of fun, and worth the small time building the kit.
In fact, I used the Grundig S450DLX as a test for the Ten-Tec BFO.
There are just a few parts, and the instructions and board layout is pretty obvious. There isn't much too it other than just making sure that the parts go in the right holes, and the banding on the diodes face the right direction. The silkscreen on the board makes it obvious.
I powered it from a single 9V battery, but had to get the battery holder wire on my own. The output consists of just two small wires you supply, or you can use maybe thin coax if you intend to solder it down to a receiver's board permanently.
Ideally you should put this thing in a metal case, which Ten-Tec also has, or you can put it into an Altoids box, whatever your fancy. For my test setup, I just let it all hang out on the desk without an enclosure. I also had a spare knob lying around, which makes it easier when tweaking the BFO pot.
How do you hook it up?
It all depends, and you have to experiment. You need to get the output wire(s) at least close enough to the radio to allow for the beat, yet you don't want it so strong that the bfo signal just swamps the front end. Sometimes you hook up the negative output ground wire, and sometimes you can rely solely on the + output wire to just capacitive couple itself into the radio.
In the case of the Grundig, below 14 mhz, I was able to just place one of the output wires along the back of the plastic case. Above 14 mhz, I had to actually clip the + output wire to the base of the antenna itself. But with my sloppy on-desk layout, there are a number of ways a decent BFO signal could be accomplished.
How do you calibrate it?
There are only two adjustments on the board - a canned tuning slug, and a fine-tuning pot. Put the pot in the center of travel. Tune your receiver to 455 khz, and tune the slug for as close to zero-beat as you can.
OR, if your receiver doesn't tune down to 455 khz, no problem! Just tune to a frequency of interest, turn the can-slug until you hear the BFO-beat zip on past, and back it in to as close to zero-beat as you can - although no need to go nuts about it, as you'll be adjusting the pot next. Now you adjust the pot until you hear the SSB or CW clearly.
Note that for withing 3 - 30 mhz, I only had to travel somewhere though just one turn of the canned-slug to land on frequency with the bfo.
Why is this casual use?
First, if you tune off-frequency a few khz, you'll have to readjust the bfo pot. In my case, below 5 mhz, I had only about 15 khz or less overall play in the pot until it ran out of steam, requiring retuning of the can-slug. When it ran out of steam, I returned the pot to the central position, and then tuned the can-slug for close to zero beat - each major change of frequency required this two-step approach.
So zipping up and down the band below 5 mhz was a tedious experience. Great quality SSB/CW, but tedious nonetheless, and I did the "retune-the-slug-dance" for large excursions in frequency.
From about 7mhz to 22 mhz, things were better. The pot itself had more coverage, and on the amateur bands in between, I only had to retune the can-slug at the band edges. But, I noticed that the actual pot adjustment getting a little tighter to make sense out of ssb.
Above 22 mhz, I had large amounts of varactor pot coverage, and barely had to touch the can-slug at all, but man, I really had to concentrate when turning the pot in extremely fine increments. Do not drink coffee above 22 mhz.
So essentially, on this Grundig S450, on the low bands, I had to retune the can-slug quite a bit, followed by fine-tuning of the pot, but this fine-tuning wasn't so finicky. As I went higher in frequency, I obtained a lot of band coverage without having to tune the slug, but just breathing on the pot could make ssb unintelligable.
In the end, this was a lot of fun, and proved that the S450 is quite capable of ssb, and stable enough to follow a 30 minute qso with only very minor touch-ups of the bfo every 15 minutes or so. But the tedium of readjusting the slug for wide-frequency operation makes it just like Ten-Tec says: casual.
I suppose if you are a utility listener, and wanted to dedicate an AM-only receiver to some spot coverage of ssb, then you could go all the way and mount this kit inside it.
For what it is, this thing rocks - it is just so much fun to use. So what's next - hey I've got a little Grundig M400 buried in a travel bag! Let's see how THAT likes doing ssb/cw !!
