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On Fri, Jun 24, 2022 at 02:28 PM, KM4TRT wrote:

other people have made this fairly simple oscillator

That's not a fairly simple oscillator.? This is a fairly simple oscillator:

Source:?

Well, I'll say this for you: you've got a heck of a lot more patience than I have!

Thanks Jim, for your insight and references, and you are right, but other people have made this fairly simple oscillator and made it work.? It's supposed to oscillate with only a cap and a resistor in place of the crystal and I can't get it to do that.
So obviously I'm missing something very basic.? Ashar made his out of the junk box.? Maybe just a cold solder joint some where.? ?Still reading.
Andy KM4TRT

Is there some reason why you have to build it completely according to the diagram?? Why not use a 100 MHz TCXO such as:





Or one of the SiTime programmable oscillators available from both Mouser and Digikey?

Or one of the many Si5351 programmable modules available on ebay?? Or the Si5351 programmable module available from QRP-Labs, also available with .5 ppm TCXO:



Or a standard 2 dollar clock oscillator, if you don't need extreme stability:



https://www.mouser.com/ProductDetail/Microchip-Technology/DSC1121CM1-100.0000T?qs=1mbolxNpo8cmMM1u4KiJ4A%3D%3D

There are a million other solutions available, don't get stuck on a particular one.? Throw the box away and think outside the box!

Hi All,?
After doing some more research, It appears that the crystal I'm using is basically good only for the fundamental.? The article says that you may not get the crystal to work at all and if it does it may be unstable. Does anyone know where to get crystals of a 5th overtone nature?? I found one company - Vectronics-? but don't know a source for them.
Andy KM4TRT

I very briefly looked at the datasheet. To me the resolution of the RSSI seem to be pretty low with only 2dBm ("Signal power in dBm = –RssiInst/2 (dBm)") whereas the Si4432 had a 0.5dBm resolution.?
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Joerg, DB2OO

This is a double post I also made on the tinySA group. It was intended to be posted here but groups.io switched to the wrong group for some reason. Anyway

Has anyone of you had a look at this chip from semtech? Since Si4432 has become obsolete I browsed for a chip that can take its place as a platform for RF tools. It has continous frequency span from 150MHz to 960MHz and comparable phase noise as Si4432 with the disclaimer that it is frequency dependant. For me, fast sweep time is beneficial as I often scan wide chunks of spectrum and this chip have a pll settling time of 30us. It’s quite good , is it? Have I missed something that makes this chip a dead end to persue further? ? ?

Link

Hi Dave,
I rebuilt the 100 Mhz oscillator on a breadboard and got exactly the same results-? 11-12 Volts going into the J310s and 2.35 on Q1 and 2.7 on Q2. .? I replaced the 22 pF with a variable all to no avail.
Also tried that on the original board.? Nothing..? I'm beginning to think that the J310's are low, but dont have a curve tracer, so I'm going to build a simple one stage oscillator to see if they work.
Andy KM4TRT

I already did, after receiving my tinySA from eleshop three days ago :). Expect new user questions soon.?

For emission and pre compliance testing you can consider to join this group:?/g/tinysa/messages
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HBTE Files section:?/g/HBTE/files
Erik, PD0EK

Hi group members
I have about 15 years as an EE developer, mostly conumer stuff. My main interest for test equipment is for debugging rf-emissions and pre-compliance testing and not amateur radio. If it is OK to discuss equipment from that perspective I am happy to join and if not I am perfectly fine with that and just keep lurking. :)

/edit
I want to add that ideas I have does not necessarily have to do with emission probing. I just like to build testgear as a hobby and learning exercise.?

All your answers seem OK and I am out of ideas and suggestions. All I can say is good luck and let us know when you get it working, maybe we will all learn something.

I am hoping that you meant J310 instead of J301 for the transistor part number. And, to reconfirm you are getting 2.3 - 2.4 Volts on each of the two sources? What are you using to verify whether the oscillator is working? What is your source for the 100 MHz xtal? Have you tried substituting a 0.01 uF cap for the xtal? It probably won't operate on frequency and changing the 22 pF cap and stretching/compressing the coils will probably let you set it about on frequency.?

Hi Dave, I found that the MPF102's pin out didnt test properly, but the J301's did.? So replaced with J301.? Now I get 2.3-2.4 volts on the source with 12+V in on drain. with no overheating.? However, it will not oscillate.? I've tried changing caps and stretching coils, but no luck.? I'm thinking that the double sided board is changing the capacitance of the circuit.? Going to try a breadboard or a circle cut board.
Andy

I would be very careful to properly identify the pin out of Q1/Q2 and also verify by testing that it is an N channel JFET. Mistakes in pinout could have 10 V forward biasing the gate to drain or gate to source, with no current limiting (since DC wise, the drain is connected to the supply voltage and the gate is directly grounded); instant smoke. These are old part numbers, Onsemi says the j310 is obsolete, don't know about MPF102. Ebay suppliers often substitute and remark other devices to supply demand for these obsolete parts, perhaps without knowing that their supplier has done that. You could get a bipolar transistor or a MOSFET. Even if its a JFET, it could be a low frequency switching device that isn't RF capable.

In reviewing the circuit design, it is my opinion that neither Q1 or Q2 are at risk of being burnt out if the circuit is properly assembled. It also won't be damaged if the xtal is bad and there is no oscillation or if there is strong oscillation at any frequency. This circuit will probably operate with either 3rd or 5th overtone 100 MHz xtals, the schematic gives no indication which to use. If you have doubts about your 100 MHz xtal, you could substitute a fundamental xtal in the 20 MHz range, which would operate on its 5th overtone or one around 33.3MHz, which would operate on its 3rd overtone. While shorting the xtal, as another commenter tried, probably wouldn't hurt anything, it would be a bit better to substitute a 0.01 uF capacitor to avoid upsetting the bias currents in the two transistor circuits, while still passing the RF signal. L10 and the 22 pF variable, plus stray circuit capacitance, forms a parallel resonant tank circuit that strongly favors the desired oscillation frequency and strongly rejects the fundamental and 5th overtone (in the case of a 3rd overtone xtal) or the fundamental, 3rd and 7th overtone in the case of a 5th overtone xtal. The xtal operates in series mode, which is low impedance at the desired frequency.

Hello Andrew / KM4TRT,
I built the SPECAN approx. 2 years ago after almost 40 years of absence from ham radio.
I also had problems with the 100MHz oscillator: I also used a MPF102 and I could tune it to 100MHz with a wire instead of the crystal. After I put the crystal in, it was not more stable than with the wire!
Due to that I decided for a different design, depicted in the Analog Devices AN-419 "A Discrete, Low Phase Noise, 125 MHz Crystal Oscillator". I only built the oscillator with the MPSH10 replaced by a BFW92 as far as I remember. Instead of the MC10ELT21 as an amplofier I used (1) an MMIC together with the ADE-1 mixer, (2) fed with a 6dB attenuator an AD831 mixer instead of the ADE-1.

Generally I have not been able, to get the SPECAN free of spurs, so that I finally abandonded the project and moved to the TinySA. The TinySA design was started by Erik Kaeshook also in this HBTE group. I built several of those following the evolution of the project.

--
Joerg, DB2OO