Fun with Russian step recovery diodes - Page 1
Forum section: electronics / rf-microwave

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: November 01, 2023, 02:54:47 am
content: I bought some 2D528 step recovery diodes from eBay (link:https://www.ebay.com/itm/204333835747).They seem to work and they generate nice combs up to 20 GHz, at least with my crude setup. I am putting in 550 MHz at 20 dBm.I'm sure my design can be improved (for example, a better biasing circuit with more inductors would allow operation at lower frequencies). It works rather well right now, though.I attached a few pictures of my design and a schematic. I am using RO4003 substrate. A 1.2mm hole was drilled into the substrate to mount the diode, and a 40AWG wire was used as an inductor.Maybe I should get a few Russian tunnel diodes too: (seehttps://w140.com/tekwiki/wiki/Russian_tunnel_diodes)

author: A.Z.
author_rank: Super Contributor
timestamp: November 02, 2023, 09:05:36 pm
content: tunnel diodes ? what about a negative resistance oscillator?

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: November 03, 2023, 01:47:29 am
content: I was thinking of making a fast pulse generator for TDR measurements using tunnel diodes, but it seems like none of the Russian ones are fast enough for that purpose (the Tektronix ones were 50mA at <1pF)

author: wd5jfr
author_rank: Regular Contributor
timestamp: November 04, 2023, 12:46:22 pm
content: Never heard of them before. How would they work as a noise generator for HF to 2 meters. I googled for a data sheet and see DigiKey has 10 for $40.72 plus others have them for less.Hank

author: David Hess
author_rank: Super Contributor
timestamp: November 04, 2023, 04:54:01 pm
content: Quote from: EggertEnjoyer123 on November 03, 2023, 01:47:29 amThe useful fast Russian ones all got bought up years ago.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: November 16, 2023, 07:57:16 pm
content: After replacing the 0603 capacitor with a 01005 22pF capacitor, there seems to be a few dB improvement.Those were very annoying to solder.Quote from: wd5jfr on November 04, 2023, 12:46:22 pmTry using a 24 volt zener instead.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 17, 2023, 01:47:37 pm
content: SRD is on the backside attached to the via then?

author: JohnG
author_rank: Frequent Contributor
timestamp: November 17, 2023, 01:54:41 pm
content: Quote from: EggertEnjoyer123 on November 16, 2023, 07:57:16 pmHmm, that is at least an honorable mention for "Understatement of the Year."John

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: November 18, 2023, 02:23:33 am
content: Quote from: joeqsmith on November 17, 2023, 01:47:37 pmI drilled a 1.2mm hole through the substrate and put the SRD into the hole.

author: David Hess
author_rank: Super Contributor
timestamp: November 19, 2023, 02:04:29 am
content: Quote from: EggertEnjoyer123 on November 18, 2023, 02:23:33 amTektronix did that sort of thing in the 1970s with through hole parts to extend high frequency performance. The more things change, the more they stay the same.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: July 06, 2025, 01:44:54 am
content: Here is the rise time of this step recovery diode as measured by my sampling scope. There is a 30dB attenuator so all voltages need to be multipled by 31.The amount of power needed to drive the SRD isn't that high, only about 200mW or so is needed. With higher power you can get to 10V p-p (at a slightly worse rise time). The USSR claims that the switching time is 50 ps, but there are probably stray capacitances somewhere in my circuit.The circuit is shown below. I think filtering might be needed because sometimes the circuit randomly oscillates (probably because the SRD does not act as a nice load). I read online that this can be fixed by using a high pass filter before putting the signal into the SRD. A schottky diode has been added to lower the amount of 150 MHz that makes it to the output (it shorts out the half of the sine wave which doesn't charge the SRD).My results match this research paper which uses the same diodes:https://www.researchgate.net/publication/341471384_Design_of_a_Low-Cost_Ultra-Wide-Band_Radar_Platform

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: July 06, 2025, 07:35:14 am
content: Here's the same measurements for a commercial comb generator.There is ripple (because there is a high pass filter in the module), but the fall time is significantly faster.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: October 10, 2025, 07:15:30 am
content: If anyone wants cheaper SRDs, they are available on Taobao for the very low price of 60 cents each.Link is here:https://item.taobao.com/item.htm?id=810034177247The seller claims they are MMD840 SRDs. The transition time is 50ps (typ) and 70ps (max) according to Macom.Here are the results with 25dBm at 200MHz fed in to the SRD.My test board has some unused pads for soldering an amplifier. That turned out to be unnecessary, and it is much easier just to buy an Aliexpress amplifier, which cost me 4 dollars. An attenuator is used to reduce the power and also prevent low frequency oscillations from occurring due to the SRD.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: October 10, 2025, 07:22:30 am
content: I also got a Herotek GC500 step recovery diode from the flea market.Here is the output spectrum. I'm wondering if commercial step recovery diode generators just use a better diode, or if I'm missing something with my designs. I think they are probably using a different biasing point. Currently, my DC bias for the SRD is zero volts, but that is probably not ideal.