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KE1GF's 455 kHz => 11 kHz down converter + neat applications

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Author Topic: KE1GF's 455 kHz => 11 kHz down converter + neat applications  (Read 7065 times)
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"Season's Greetings" looks okay to me...

« on: January 16, 2006, 01:57:06 PM »


I recently built a 455 kHz = 11 kHz down converter using a schematic that was sent to me by Bill (KE1GF). Bill was kind enough to give me permission to disseminate it, along with information about how to get the parts, and how to use it.

I think you will find it to be an extremely useful device, which you can easily build for around $20.00 (the cost of the parts)... and which works in conjunction with the existing sound card of (almost) any plain vanilla computer.

To see the schematic and the associated information... including a screen shot of the r.f. spectrum of an AMer, taken off the air with my receiver => Bill's converter => my computer => a freeware application called Spectrum Laboratory (that you can download from the Web)... go to my Web page:


Best regards

Stewart ("Stu") Personick. Pictured: (from The New Yorker) "Season's Greetings" looks OK to me. Let's run it by the legal department
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« Reply #1 on: January 16, 2006, 02:38:01 PM »

Thanks for posting this Stu.

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« Reply #2 on: January 16, 2006, 03:49:01 PM »

Stu, for a few more bucks I am trying to do a I/Q converter. I'm taking the flex front end with a couple modifications. 2- 74ATQ74s as a divider chain and I/Q LO generator and the simple crystal oscillator and comparator from the soft rock circuit. A color burst crystal will give a 8.44 KHz IF to the sound card stereo inputs. Spectrum monitor and SDR demodulation.  KISS. This could be used as a SDR interface to an antenna with a preselector ahead of it. The plan is a simple building block for doing SDR. It will work with SDR software and 3 other packages I have downloaded free.
Just yank out the crystal and add a synthesizer and you have a SDR receiver.
I figure under $40 for parts.
BTW bills circuit will work with sdradio.org ver .99 demodulation software. fc
Johnny Novice

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« Reply #3 on: January 16, 2006, 08:32:23 PM »

Frank, in keeping with the spirit of things, you gotta get that cost down to $20 + a handful of FETs.

FCC:  "The record is devoid of a demonstrated nexus between Morse code proficiency and on-the-air conduct."

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« Reply #4 on: January 16, 2006, 10:34:20 PM »

John,  express pcb will run $17 if we are lucky. My drafting friend talked me into the same inst. amps used in flex rather than op amps. There is another $10 up from $8.
then 2- 74ACTQ74 for the divide by 8/ I/Q generator, the dual mux for the double balanced tayloe converter. stereo and SMB connector.
Color burst crystal $0.50, 2n3904, Comparator, 7805 for the oscillator. hand full of caps and resistors.
The price has gone up about $5 since yesterday being talked into better parts and local voltage regulator.
I figure it will be around $40 to $50

There will be enough provisional jumpers to make it a flex front end. Flex used relays to change the gain of the inst amps. That would be against my religion to put a relay in an amp feedback loop.

our goal will be to make a couple boards to plug into our 6830s. I will be glad to share the design since it is mostly a modified copy of flex and soft rock. We may have someboards made.

How many of us have talked about sync detectors. now it can be done cleaner with a dsp with the added attraction of a spectrum display and variable bandwidth. also it can be connected to just about any IF. I tried the fT1000 board as a converter and the pll is a pita. This can be connected to any 455 KHz IF with only an attenuator value change. I cant make it any more simple. Now if I just take the soft rock 40 circuit and convert it to do a color burst crystal it might save $5 to $10 so why not go for the best configuration rather than cheap out.

I'm fresh out of 1N34 useless diodes.
« Reply #5 on: January 17, 2006, 02:31:44 AM »

Here's some nice eye candy that I created to help me design the input to the 80M 2FET driver.


Of course these graphs were made with theorectial FET gates, but I added some entropy to make it close. A real RF switching FET you're going to have miller capacitance varactor effects, packaging inductance. Because they are included in the module.

Speaking of simulation I've found tht IXYS has the best models that I've seen yet. There big bucks per pill but depending on the application, like MRI, NRMI and RF heaters Angry they are well worth it.

-Bil 'GF

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« Reply #6 on: January 17, 2006, 09:11:01 AM »

I notice the gate source loads. Yup they pull it resistive very well. I just put some in my 160 meter final to square things up. I kept adding them until the peak gate voltage dropped to 12.5 volts. My driver is running class d at about 30 watts input.
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