Comments for "Heterodyne Sweep Generator"

6th December 2014 05:33

Peter wrote ...

Schematics please.

I will probably try to go from the source you started, and have to ask u some questions.

You need/want some SFE7.02MU Ceramic resonators?

Udo/DL2YEO uses them wittily in his designs on QRP4U site.

I also have ne592's if needed.

I would gladly mail to you.

The 7.02 CRs are as rare as hens teeth except in industrial volume. They can be push/pulled from 7.00-7.04 . Also the harmonics are in the right places for CW

Peter ;)

18th March 2012 04:07

Giacomo Bovio wrote ...

Hi Alan,

I am an old italian radioamateur and I like your Heterodyn sweep generator for my lab. Could you send me the schematic?

Thanks a lot.

Best Regards


6th February 2009 13:18

Alan Yates wrote...


Those hetrodyne extender jigs are very handy aren't they. I have a 512 MHz one for my dodgy spectrum analyser that mixes-up HF to its UHF range. I've also used it with my VHF signal generator for signals on 70 cm.

All the good marker generator circuits I've seen appear to be mixing schemes of some sort (although I've also seen simple window comparator schemes driven off the sweep and calibrated manually - yuck). Some have an xtal filter to sharpen the pip, or use a differentiator. A simple scheme might use a 10 MHz xtal so the maths is easy, just add/subract 10 MHz to whatever the counter on the other generator says.

Here is an interesting one, very simple in an old tube generator:

Also, I rather like this one, it is a harmonic mixer and differentiator to make a comb of equally spaced pips:

This is something I have in mind for my hetrodyne generator if I ever finish it.



3rd February 2009 08:02

Jeff -VE3AK wrote ...

Hi Al... I tripped over your site looking for "Post Marker Injection" and how to do it. Nothing found so far. However, I just finished building a simple circuit so I could use the Marker in my old Wavetek. Since the Wavetek I have is from about 25Mhz and up, and no good for IF alignment and experimenting with filters etc. I fed a 25Mhz self contained IC into a SLB-1 and fed the Wavetek into the other port of the SLB-1. That all comes out into a 25Mhz LP filter I feed to the filter under test. It works and the marker can be an external one fed into the back of the Wavetek... So far, I can see the marker but it is too wide to work with. However, the 2Mhz filter can be sweept and looks good with this combo. regards Jeff

5th December 2008 11:40

Alan Yates wrote...


I haven't tried modelling that kind of VGA before, but I've seen the topology, I think either in EMRFD and/or on the popcorn site... Seems quite logical, use the MOSFET as a variable degeneration resistance.

I do have a good spice model of a very simple ALC system for narrow-band use, but it is class-C with collector modulation, so it can't operate over an octave without switched and rather aggressive low-pass filters. Basically the detected DC feeds a NPN transistor base who's collector load feeds directly into the VGA control port. The collector voltage drops with more base current from the detected signal so the VGA gain is reduced. As long as the gain and time constants are reasonable the loop works great in a transient simulation in spice, stabilising in about 50 us - it is slightly under-damped but that isn't a big deal or too hard to fix.

The same general approach would work for the VGA I've got working, I just need to draw it up in spice (or build it). The low-distortion VGA has the advantage that it doesn't mess up the waveform and generate all kinds of harmonic energy, so the filtering at the output can be less critical. I don't want to use an IC VGA myself, as you know I like to build with discrete transistors when they are sufficient - even to the point of avoiding op-amps for the ALC loop amplifier.

I toyed with the idea of using a PIN attenuator, but I've largely given up on that for now. Might come back to that later, a PIN quad IC and a few MMICs would be a clean and easy way to achieve a levelling loop at higher frequencies. Over the next few days I'll post all the spice files of the various VGA approaches I've fiddling with in silico. They are all useful in their own right, so as building blocks for other applications they would be handy to have documented. I'll have to try the MOSFET degeneration approach too.



5th December 2008 04:34

Arv - K7HKL wrote ...

I wonder if your variable gain amplifier and related ALC control might be just a BJT amp with the emitter bypass cap in series with a MOSFET. By providing some rectified RF as DC feedback to the MOSFET gate you might be able to get enough gain control to meet your needs. If workable, this could be a more reproducable approach than using some possibly essoteric variable gain wideband RF IC.



4th December 2008 15:51

Alan Yates wrote...


Yes indeed. Once I finish it I'll write it up fully with circuit diagrams, etc. It is work-in-progress at the moment. The ALC loop in particular.

The usual disclaimer applies: So many projects, so little time! Although I've been getting better about finishing stuff off to completion of late. This device in particular is important for several other projects (believe it or not, but I drew a graph of the dependencies between my various projects to work out what to attack next) so there is quite a bit of incentive for me to get it working ASAP.

One thing I am kinda confused about is how to box it up. The individual modules would be handy to have as removable units, but it would also be nice to have it all in one small box for portability... I guess I can just rebuild the modules - I've made them once after all, another time is easy. So it is a big diecast box, or lots of Altoid tins inside an instrument case... Decisions, decisions.



4th December 2008 14:33

Arv - K7HKL wrote ...


As usual, an interesting and intriguing article. I assume that this "teaser" introduction will be followed by schematics, and such?

Arv - K7HKL

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