Author Topic: Frequency doubler 10 - 20 MHz (Read 23549 times)

Bud · « **Reply #50 on:** June 29, 2021, 11:18:33 pm »

OP said he does not want "stuff", didn't he. The expectation was to feed 10MHz into a magic component and get a clean sine of same amplitude on the output.

Gerhard_dk4xp · « **Reply #51 on:** June 30, 2021, 07:08:52 am »

Not metrology grade, but this could fit the bill:

< https://www.digikey.de/products/de?keywords=NB3N511 >
< https://www.digikey.de/product-detail/de/renesas-electronics-america-inc/511MILF/800-1039-5-ND/1915340 >
< https://www.digikey.de/product-detail/de/renesas-electronics-america-inc/511MILF/800-1039-5-ND/1915340 >

eb4fbz · « **Reply #52 on:** June 30, 2021, 09:27:46 am »

RF Splitter and balanced mixer = Frequency doubler with good rejection to other unwanted products. Loss will be about 9-10dB.

bob91343 · « **Reply #53 on:** June 30, 2021, 05:35:32 pm »

I am still leaning toward the two-transformer-diode-bridge circuit. The Renesas 511MILF might work but its output is a clock, not sinusoidal.

TimFox · « **Reply #54 on:** July 01, 2021, 06:30:52 pm »

By coincidence, I received a promotional e-mail from Pasternack about their frequency multipliers. Interestingly, they have doublers that are all passive and therefore have insertion loss, but their triplers are powered (+12 V) and have insertion gains. The range of doublers goes down to 10 MHz input, but the triplers start at 250 MHz. I didn't check, but I assume they are more expensive than the MCL units I cited in my first response, and are built in aluminum boxes.

bob91343 · « **Reply #55 on:** July 01, 2021, 10:23:25 pm »

Everything from Pasternack is outrageously expensive. I am still working on my own doubler using a bridge rectifier but so far have nothing that works well.

TimFox · « **Reply #56 on:** July 01, 2021, 10:31:37 pm »

Pasternack stuff is high priced, but very high quality. The MCL units are reasonably priced and can be trusted.
I found it interesting that all of the triplets were powered, but all the doublers were passive.

bob91343 · « **Reply #57 on:** July 01, 2021, 11:14:30 pm »

The reason for such strange situations is usually that someone had a requirement, they built a unit, and then put it in the catalog. Apparently nobody wanted a powered doubler.

TimFox · « **Reply #58 on:** July 01, 2021, 11:35:36 pm »

More likely, there is a good reason for powering the triplers, and they advertise a series of units covering a range of frequencies. Pasternack makes custom-length cables, but most of their other stuff is catalog items. Also, the doublers go down to 10 MHz, but the triplets are higher frequency with relatively low bandwidth.

(Stupid spellcheck changed that to “triplets”.)

bob91343 · « **Reply #59 on:** July 02, 2021, 03:59:49 am »

Well I am not looking for a 'reasonably priced' item from Pasternack. This is a hobby and I have very little discretionary money for trinkets. If I were a working engineer again, it would be different.

TimFox · « **Reply #60 on:** July 02, 2021, 01:24:41 pm »

Then buy one from MCL, like I posted much earlier. "MCL" is MiniCircuits Laboratires, not a part number from Pasternack. I only mentioned Pasternack as an example of what the professional vendors are supplying and said it would be more expensive than MCL. My exact wording was "The MCL units are reasonably priced and can be trusted.", as a comparison to the expensive premium parts from Pasternack.
In general, when dealing with non-linear circuits like frequency doublers, you will need both gain (from an active circuit) and a resonant circuit or other filter to remove unwanted harmonics.

bob91343 · « **Reply #61 on:** July 02, 2021, 06:29:51 pm »

Thanks for the clarification, Tim. Where can I buy that unit? How much are we talking about, for cost?

Meanwhile I am struggling to make this home made circuit work. I might succeed, when I get to spend more time on it.

TimFox · « **Reply #62 on:** July 02, 2021, 06:57:51 pm »

The MCL website sells the lower priced units (roughly $6.00) with minimum quantity of 10. Several of the usual vendors (Mouser, Newark, etc.) come up in a Google search for MiniCircuits vendors, but I haven’t chased further. MCL has a huge catalog, based on their core technology of toroidal RF transformers.

Bud · « **Reply #63 on:** July 02, 2021, 08:49:43 pm »

You can buy Minicircuits stuff on eBay but do not buy from China. It will be counterfeit and not to specs.

bob91343 · « **Reply #64 on:** July 02, 2021, 10:57:42 pm »

Well it looks kind of grim. MiniCircuits is cheap but I have to spend $60. No way. Chinese vendors are counterfeit so I can't buy from them.

Looks like a no-win situation.

bob91343 · « **Reply #65 on:** July 03, 2021, 12:32:31 am »

All very true. I was hoping to avoid an active solution. The only reason I suspect a sine is best is because this is going to substitute for a crystal. I could of course leave the crystal in and drive it with 20 MHz which would certainly provide the accuracy I want. (The driving signal will be very accurate.)

Since it's a crystal oscillator load, it should end up just being synchronized by the source, which is fine for my purpose. But I can't synchronize it with 10 MHz. At least I don't think so.

TimFox · « **Reply #66 on:** July 03, 2021, 03:34:22 am »

OK. Take a single transistor, bias it appropriately, and run it into a tuned circuit (tuned to the second harmonic).
Have you tried Google to locate a vendor who will sell you a cheap MCL doubler in singles? I leave it as an exercise for the reader.
Several of my classic test instruments that use an internal 10 MHz clock can take an external 5 MHz drive and run it through a 10 MHz crystal to get a high-quality clock.

bob91343 · « **Reply #67 on:** July 03, 2021, 05:00:49 am »

Tim, tell me more about the synchroniation you mention in your second paragraph. If they can synch a 10 MHz xtal with a 5 MHz signal, I should be able to do the same at double those frequencies.

TimFox · « **Reply #68 on:** July 03, 2021, 01:45:45 pm »

It's not really synchronization, it's using the 10 MHz crystal in a crystal filter circuit following an input amplifier that distorts the 5 MHz sine wave so that it contains second harmonic content.

bob91343 · « **Reply #69 on:** July 03, 2021, 05:17:38 pm »

I was thinking along those lines. Do you have more information?

TimFox · « **Reply #70 on:** July 03, 2021, 05:28:17 pm »

This will take some time, but I’ll try to refer you to an instrument manual.

TimFox · « **Reply #71 on:** July 03, 2021, 07:24:02 pm »

See the manual for the PTS-160 frequency synthesizer, http://manuals.repeater-builder.com/te-files/MISCELLANEOUS/PROGM%20PTS%20160%20Instruction%20Manual.pdf , from Programmed Test Sources (ca. 1980).
The manual comprises separate sections for different modules, with the pagination restarting at each. The maximum output frequency is 160 MHz.
The relevant section is pp. 65 to 80 of the .pdf file, with the crystal filter shown in the schematic on p. 77.
As described in the manual, either 5 or 10 MHz can be applied from an external standard, and the filter produces a 10 MHz reference for use by the modules.
PTS made several variations on this design, with different frequency ranges, and at my former employer I believe we had a 40 MHz version.

TimFox · « **Reply #72 on:** July 03, 2021, 08:02:55 pm »

The PTS-160 is all BJTs and digital ICs.
Gerhard_dk4xp, in reply #50 to this thread, mentioned a multiplier using a JFET.
An advantage to the JFET over the BJT in this doubler application is that if you apply a decent sine wave to the gate, strong enough to get a non-linear response, but not so strong as to switch the device ON/OFF, in theory the output of the FET (quadratic response for ideal JFET) will contain only the fundamental and second harmonic spectral components, while the BJT (exponential response) will contain the fundamental and all integer harmonics.
Since neither a pure sine wave nor an ideal square wave contains anything at the second harmonic, something must be done to distort the waveform before extracting the harmonic. Applying a sine wave to a device with even-harmonic distortion gives an asymmetry between the "goes up" and "goes down" parts of the waveform, shifting the zero crossing away from the center of the period, and thereby generating even harmonics. If the distortion is odd, then the "goes up" and "goes down" both get distorted from their ideal sinusoidal shape, but the zero crossing stays centered, thereby generating only odd harmonics.

bob91343 · « **Reply #73 on:** July 03, 2021, 11:15:12 pm »

It seems that there is no simple answer to this. I haven't gotten back to the circuit to try to generate 20 MHz but might do so this weekend.

Even a single diode should work. Its rectified output will be unipolar, thus containing even harmonics. I might try that instead of a bridge. I have yet to study the transceiver circuit to see what might work. Up until now it's just been a thought, nothing more.

Bud · « **Reply #74 on:** July 04, 2021, 01:34:44 am »

Quote from: bob91343 on July 03, 2021, 11:15:12 pm

It seems that there is no simple answer to this.

Glad you realized this !

Quote

Even a single diode should work. Its rectified output will be unipolar, thus containing even harmonics.

To maximize 2nd harmonic content your diode should only conduct for 120 degrees out of 180 unipolar. Look up "conduction angle" in relation to harmonics content for details.


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Author Topic: Frequency doubler 10 - 20 MHz (Read 23549 times)

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