Ham Radio Magazine: harmonic mixer K1ZJH 40 Mar 85

This little device will downcovert or upconvert a signal from a generator by mixing it with a 50 MHz internal crystal oscillator, the mixer is a passive MCL DBM. Total parts cost was under 20 bucks at the time.

If there is enough interest I'll try to find the info and post a schematic and parts list on here. This is not in the same league as the HP-11710B; but it will let you do a lot more with a limited range generator. 50 kHz IFs, etc. are easily handled by any generator.

Pete

I might be persuaded to reinvent the wheel, and do a construction project for ARF. More modern 50MHz DIP packaged oscillators have hit the market, and cost pennies. When combined with an inexpensive MCL DBM mixer you will expanded generator coverage above and below your generator's coverage limits.

Pete

Hi Peter,

It sounds interesting... BTW, I own a couple HP-11710B. One was got back when there was a big surplus of NIB units on ePay. In fact, that one is still unopened on its long term storage packaging.

Some months ago, I got another unit, used and in AS-IS condition. But it was pretty cheap . And it just needed some cleaning, both externally and electrically (dirty switch contacts). But it was otherwise perfect and works fine

But, you know, you never have enough test equipment

Regards,

JOSE

PS: here you have some pictures of my last acquired unit, as I got it and then after I worked on it:

I'm not sure if I would build it but I would be interested in hearing more about it.

Rod

Mine was brand new in the military box... never used )

Doesn't sound like too much interest, so I'll hold off on the project.

Pete

I for one would be most interested...

Don

<AOL>
Me Too!
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I always read those sorts of things over closely to pick up what I can...

(Yes, I've a 11710B, but who knows when I might have need for two.............)

Okay, lets make it a poll. I'll start one. There are several approaches.

Pete

The mixer in mine was blown but amazingly Mini-Circuits still makes the part, so all I had to do was call them up and order a new one.

-Matthew

It would be added work up-front, but I wonder if the design would be applicable to a down-conversion of 30 or 35 MHz?

Being able to build one for a different frequency offset could make it more usable with other generators/sweepers.
There are plenty of such instruments that do not have digital frequency control, and have ranges/bands at various "odd, analog" frequencies.

I'm interested. I want to use my Boonton below 125Khz sometimes. Instead I have to switch to a flaky B&K function generator.

Tony

With many having synthesizers and/or counters, a stable mixing signal is often available using the internal time base signals available at the rear panel of most of those units. !, 5, and 10Mc time base signals are available on different counters and synthesizers so just about any sweeper can be used with it I'd think.

Excellent point, Mike... a 1 MHz reference would make a good LO to drive a mixer. Most DBM diode mixers are rated for 7 dBm LO injection, so I'd expect the LO level might be a bit shy of what is needed. But, it would work.

Pete

+7dbm is around a volt and a half P-P, so I'd think TTL outputs, which I'd guess most older gear would have, could certainly do it. If such turns out to be the case, we're looking at a really low parts count widget here, a balanced mixer and a couple of clip leads.

I looked at my Boonton 103D last night. The reference output is halfway between a square wave and a sine wave (think square wave through a series resistor to a shunt capacitor). It reads about +10dbm (2.x volts peak to peak) into no load on the SLM at 1Mhz and about -7dbm with the SLM input at 75 ohms.

Tony

That is good news, Tony...

So, a cheap MCL doubly balanced mixer package (about seven bucks, shipped) and a small minibox with three BNC fittings would provide an easy way to generate signals below 500 kHz using a good quality generator.

One could use either a 10 or 1 MHz reference output, and the generator output, to produce IF signals below 500 kHz. So long as the generator is stable at 10 or 1 MHz, the output can be taken from the IF port of the mixer, and it would be good down to DC! That means it could produce an usable signal down to the audio range.

If one wanted to get fancy, some LC filtering could be added to reduce the spurious mixer products.

Pete

Yay! The General Radio BFO gets reincarnated in digitally synthesized form

Steve said;

But this is lots littler.

This should give quite a few fellas here a step up, and, mounted in a tiny cast box as Pete suggested, you just toss it in the Junque/coax adapter/attenuator drawer, for future reference.

If I had an 8640B or one of those Boonton 102/103’s that don’t cover down low I would be all for something like this.

-Mark-

I've got a Boonton 202-G that's set up for an obsolete VHF telemetry band: 185 to 270 megacycles. I've been thinking about making a downconverter for it to make it useful. I have some precision 50.000000 MHz TxCOs with TTL output; I figure mixing with the third harmonic would let me output 35 to 120 MC.

I found an MCL mixer that should work on ebay for 7 bucks shipped so I ordered it. We will see how well this works.

Tony