555 Super-Regenerative IF HF Spectrum Analyser - Page 1
Forum section: electronics / projects

author: lordvader88
author_rank: Frequent Contributor
timestamp: June 16, 2019, 06:13:20 am
content: I'm finally making this project in full, and I hardly know anything about JFETs.http://www.vk2zay.net/article/256This uses J310's, I have J112, J176, 2N5485, is there much difference ? I could try allI've made L1,2,3, with I think 22AWG phone cable, however it has the plastic insulation left on, IDK if that matters or not for RF inductors.I have an LCR meter, it only go's up to 100kHz, so IDK how the real life inductance changes across frequency. It reads different inductance at 100Hz than 100kHz.For the 4x 170nH inductors, I don't have the real type of ferrite cores. I just have cheap green and yellow ones, about the right diameter, from ebay. So I don't know the core type.But I have the rest of the parts and copper clad board too. Hope this works and looks cool

author: ChristofferB
author_rank: Frequent Contributor
timestamp: June 17, 2019, 05:42:35 am
content: The core material of the toroidal matters quite a lot. I'd recommend getting a bag of the right ones, there's no rf components I love more than standardised toroids. They tare so much guesswork out of circuit design, and there's a website called toroids.Info that will let you calculate wire length from core type and wanted induction, it's great!Wire insulation shouldn't matter much, as long as you can fit the right number of windings still.I suspect most of those jfets would work, but I'm not certain.Remember small stiff vhf coils are easily tuned by just changing the distance of the windings with a plastic stick or a bamboo skewer!Let us know how it goes, I've been eyeing that project for some years!--Chris

author: lordvader88
author_rank: Frequent Contributor
timestamp: June 17, 2019, 01:15:22 pm
content: Well I made is but I had to use open air coils to get 170nH coils for the input filter. So IDK how much that will really matters as the LP filter. I'm using the VHF 2n5485.IDK if it's working or not. I'm only inputting the very weak signal from a xr2206 signal generator. It has very little drive, and works up to 3.8MHz. The ramp-gen is working, 2 JFETs in the mixer are on but I think only barely. The LO JFet seems off. The detector output is only at 0.4Vdc atm, and the AC is barely 5mVI'm new to JFETs. So far I've not seen any real voltage on the Y output at all.I could try driving a BJT from the xr2206.I'd like to adapt this to much lower frequency, but IDK how the JFET biasing works or their RLC parts. I should play around in LTspiceI should make a JFET Hartly or Collpits oscillator again to see 1 working again.

author: mikerj
author_rank: Super Contributor
timestamp: June 18, 2019, 07:51:25 pm
content: The 2n5485 has a lower Vgs(off) voltage range and a much lower Idss range so it's unlikely the original biasing arrangement will work well.

author: lordvader88
author_rank: Frequent Contributor
timestamp: June 19, 2019, 12:07:58 am
content: If it was working, what to u think the JFETs in the guy's working circuit should be doing with no input ?I'll try new JFETs, but maybe it's just I haven't used a strong or high-freq. enough signal. I just made a little crystal oscilattor. If I just try amplifying that a few times, but to what level ? And if I actually make something that can drive 50 or 75ohm load, what current and voltage is that atIs this thing meant to work with AC input coupling as well ? The 56ohm resistor on the mixer JFET is only 1/4 atm, I don't see any big resistors in his case.Aside from the ramp gen, should anything be oscillating from say a tank circuit when the circuit is turned on ? Should the LO be doing anything? Or does it only follow an input frequency? If this was an all BJT circuit, I'd know what to expect a lot better.I made Mr.Carlson's Super AF/RF probe, it works great. It doesn't hear much from the 555 SA.On XY mode, I though I found something that looked like it might be real, but I was looking at clouds.So if the JFETs were biased about right, when turned on, roughly what should the DC voltages be on GDS, and several of those are on Vcc and GNDI must experiment with single JETS