Re: Microwave mixer diode substitutes
Sulaiman, Thu May 18 2017, 06:22AM

I use BAT62-03W at 100's MHz, I believe that they work into the GHz range,
from the datasheet, BAT15 work to 12 GHz and are available as singles or duals or ring.

Re: Microwave mixer diode substitutes
Proud Mary, Thu May 18 2017, 07:47AM

The BAT15 looks promising and a big cost saving!

Thank you so much! :)

Re: Microwave mixer diode substitutes
Proud Mary, Thu May 18 2017, 08:49PM

Sulaiman, I bought five SMD dual BAT15 for £3.99 and they do look very useful as follows:

Qty. 5 New Infineon Schottky mixer/detector diodes. These are dual independent diode devices.

High sensitivity detector with low forward volts drop and low junction capacitance Due to the low barrier construction and low series inductance this device will operate as a mixer to 12Ghz

Very low forward volts drop 0.23V at 1mA
2 independent diodes on the 1 package, allows a detector with simultaneous positive and negative outputs to be constructed or use as a single detector with the other diode used for DC temperature compensation. Can also be used in a voltage doubler configuration.
Low junction capacitance 0.5pF typical
Operation to 12GHz
Allows greater flexibility for projects as the diodes are electrically independent of each other
SOT-143 4 lead package SMD Code S5s

A big difference pricewise to the 1N21 NOS microwave mixer diode at £6 each!

Thanx for the heads up! :)

Re: Microwave mixer diode substitutes
Sulaiman, Thu May 18 2017, 09:28PM

You may also be interested in pin diodes for switching or clamping, HSMP-382x series.
I have the 3822 type, quite useful for switching, but I've not worked at GHz.
also useful as a clamp on the antenna input etc.

I hate those stupid 4-lead SOT-143 SMDs ... prototyping is a pita

and note the BAT15 PIV rating ... 4 V !

Re: Microwave mixer diode substitutes
Proud Mary, Thu May 18 2017, 10:40PM

My basic concept for the UHF impedance bridge is adapted from a simple ham design that drives a panel
meter directly, but I can see that in order to keep the RF test signal voltage down to a safe level for the diodes, I'll have to amplify the output to drive the meter (a very nice Russian 100μA model with an arc of mirror). I've got a few OP07 and I'm sure that will be all I need for amplification at this stage.

I have very little experience of SMD construction, and what experience I do have tells me to avoid using those horrible little parts at any cost, but there's no way I could get my Z bridge to motor over 1GHz or so without using them.

I have another ham design for a Z bridge that the author claims is good to 3GHz, which it manages by miniature design. If I can make it work at 2.5GHz I'll be over the moon, as the claimed maximum frequency of my Nooelec NESDR SMArt SDR is 2.35GHz, and that of my Thumbnet N3 SDR 1.766GHz.

I'll put up some pictures when I've got something to show for it (parts heading my way from China at this moment!) in case anyone else is interested in designing UWB antennas for SDRs.

Re: Microwave mixer diode substitutes
johnf, Fri May 19 2017, 06:59AM

1N5711
are some of the best they do do a surface mount version but I use the legged version 2 pf junction capacitance is about as low as you can go and VF starts at 0.25 volts so equiv to germanium

Re: Microwave mixer diode substitutes
Sulaiman, Fri May 19 2017, 09:53AM

I've used quite a few 5711s, they are excellent at VHF (2m)
(e.g. compared to 1N4448/1N4148)
I doubt that they will be much use at 2.3 GHz, but have not tried,
at 2.3 GHz the wavelength is about 100mm on a pcb,
so the overall length of a 5711, even with short leads, becomes a significant part of a wavelength,
if you are smart you can compensate for this ... I can't.

EDIT: I stand corrected,
I just googled "5711 GHz" and found lots of 2.4 GHz detectors etc.
but based on capacitance, (at 2.4 GHz, 1pF = -j69R)
1N4148 4 pF
1N5711 2 pF
BAT62 0.35 pF, 0.6pF max
BAT15 0.35pF max

Re: Microwave mixer diode substitutes
Hazmatt_(The Underdog), Fri May 19 2017, 04:05PM

Check Minicirciuits. They have mixers, couplers, detectors, everything except isolators (not sure why that is), and they are reasonably priced.

Shipping may be unreasonable though because they're here in the states.

Re: Microwave mixer diode substitutes
Proud Mary, Fri May 19 2017, 04:37PM

Thanks guys - quite a bit of experimenting to be done with all these suggestions! :)

Re: Microwave mixer diode substitutes
Proud Mary, Sat May 20 2017, 11:48PM

Sulaiman, the BAT15s came super quick in the post today, and they are even smaller than in my nightmares!

My first step has been to send off for a better magnifying glass!

Re: Microwave mixer diode substitutes
Sulaiman, Sun May 21 2017, 08:51AM

O O
\_/


can't say I didn't warn you

At work, stupid-small smd components have come to be known as 'fleas'
I could not understand why for months, I thought it was because of the size only,
until I found how easy it is for them to leap over a foot through the air when handled by tweezers,
they usually land in a pile of something then hide

I remember my first job in the early '70's when an older colleague was complaining to me about
having had to move from 0.15" veroboard to the stupidly small pitch of 0.1" due to dil ICs
... now I'm the grumpy old guy !

I think that miniaturisation is just a sneaky way of removing older, higher-earning, poorer-sighted employees
to make way for younger, cheaper, more energetic youth.
It's a conspiracy !

Re: Microwave mixer diode substitutes
Proud Mary, Mon May 22 2017, 06:30PM

Here is the circuit diagram of my first UHF/SHF project.

The author, Mr Paul Wade, N1BWT, relates that he took the circuit of an existing VHF VSWR meter which was good up to 450MHz, and effectively translated it into the UHF/SHV domain by specifying all components as chips.

N1BWT comments: "Now that we've gone to the effort of using chip components and making the VSWR bridge as small as possible, how much have we gained? With good 50Ω SMA terminations at J2 and J3, return loss was greater than 30 dB (VSWR > 1.2) from 10 MHz through 2304 MHz, while at 3456 MHz, the return loss was 22 dB (VSWR = 1.9), so performance is degraded but still usable. However, at 5760 MHz it was worthless. So we have increased the upper frequency limit to at least five times as high as the original version. It is possible that this style of VSWR bridge could be pushed even higher in frequency by making it even smaller, using tiny (and more expensive) microwave chip capacitors and resistors."

Exciting stuff, but it means I've got to learn what for me is a new technology.

Re: Microwave mixer diode substitutes
Sulaiman, Mon May 22 2017, 07:50PM

I think that you may be employing the wrong topology,
google stripline swr e.g.

Re: Microwave mixer diode substitutes
Proud Mary, Mon May 22 2017, 09:41PM

Thank you for that reference, which I shall read with interest.

My plan for now is just to follow the circuit and copy the PCB diagram as best as I can from Paul Wade's 1995 article A UHF+ VSWR Bridge here:

The article seems well thought through, and modest in its claims, but would I notice even the most terrible of errors? I'm not so sure!

As for getting things wrong. I don't know very much about this subject, and am sure I have gotten a lot of things wrong - but don't yet know what they are. If the day arrives when I get more right than I get wrong, I shall count myself a fortunate person! :)

Re: Microwave mixer diode substitutes
Hazmatt_(The Underdog), Tue May 23 2017, 02:11AM

from 1GHz and up you want to use back to back directional couplers and detector diodes, or a pre-fabricated detector, and a circuit to compare forward to reflected to give you VSWR.

Couplers are very wideband if constructed well, and are accurate.

Re: Microwave mixer diode substitutes
Proud Mary, Tue May 23 2017, 06:06PM

Thanks for that, HazMatt.

I don't as yet know very much about it - but better late than never - so I am going to continue with the UHF+ VSWR project as I've ordered the parts - some have arrived already from China - and the author seems a very knowledgeable fellow who gives enough info about the circuit, including the all-important board layout, for me to proceed quite quickly once I've put in some flying time soldering/desoldering junk chips to/from scraps of board.

From what I've seen of hobbyist SDR so far, most - but by no means all - hobbyists are dependent on kit designed and constructed by other people, with the result that there are plenty of part-assembled kits and modules for listening in to air band, satellite weather, listening in to the cops, and so on, and not very much about, for example, radio astronomy.

Anyway, I'll keep everyone posted on my first UHF/SHF project, and maybe get some good advice if things do not always go as hoped! :)

Re: Microwave mixer diode substitutes
Sulaiman, Sun Jun 04 2017, 07:15PM

Radio astronomy is a non-starter for most of us due to antenna size and antenna positioning requirements and background noise.

The only achievable stuff is solar and Jovian observation, e.g.

Re: Microwave mixer diode substitutes
Proud Mary, Sun Jun 04 2017, 10:22PM

May 29, 2017
Detecting Pulsars with a Circularly Polarized Yagi and an RTL-SDR

I don't have anywhere to put up even a modest antenna like this one, so your point is well made, Sulaimann, but is is nonetheless remarkable that radio astronomy that could only be undertaken by major institutions is now within the grasp of committed individuals.

My dismay at finding I could do nothing at all with the jumping flea SMD chips has been reversed by a compromise that took me ages to fall upon due to my unfamiliarity with the technology. I can nothing with 100 pF 50V chip capacitors, but found that 100 pF 1000V was just about big enough for me to use my standard soldering skills. The same with chip resistors: I can work with the 2W ones just fine! This still means that I shall not be able to reach the higher microwave frequencies, but is still a big advance over my previous thru-hole axials in the direction of miniaturisation.

Re: Microwave mixer diode substitutes
Dr. Slack, Mon Jun 05 2017, 06:10AM


Are you sure that the limitation is that you can *do* nothing? I used to think I didn't have the control skills to solder small stuff until I used a decent microscope. Then I realised it was simply because I could *see* nothing. Once I had sufficient gain in my optical feedback path, I found I could achieve good connections with 0402 parts routinely, and 0201 with a bit of care. Even stacking an extra pair of +4 reading glasses over your standard ones can bring about huge improvements.

Re: Microwave mixer diode substitutes
Proud Mary, Mon Jun 05 2017, 01:54PM


I'm sure you are right and that there is an element of that in it. And yes, good magnification is essential, but I still have to deal with unsteady old hands that first held a soldering iron 50 years ago. Starting with the larger components, and then working my way down in scale when I have acquired a bit of skill seems a sensible way to go. :)

Re: Microwave mixer diode substitutes
Sulaiman, Mon Jun 05 2017, 02:36PM

Detecting Pulsars .... from the link posted it seems that ONE or TWO are actually detectable by amateurs, not a very exciting prospect.

My two as yet unfulfilled radio aspirations are
. chatting with ISS astronauts/cosmonauts
. earth-moon-earth communications. (moon bounce)

I have not worked with 0201 smd, 0804 is as small as I want to go.
I prefer 0.1" matrix and through-hole components but like me they are now obsolescent :(

Re: Microwave mixer diode substitutes
Proud Mary, Mon Jun 05 2017, 04:05PM


I've seen people who've broken the bank making costly subterranean inductors of enormous size to detect the Schumann Resonances, but find themselves with nowhere to go once they have the Resonances resonating on the screen in front of them. So I think you are right about the pulsars pulsing away if you can detect them to which I'll add detecting the 21cm Hydrogen Line which is a goal of some rtl.sdr enthusiasts. Years of observation and something might change but otherwise it is hard to go further.

What I do find exciting is ultra-narrowband (1 Hz!) communication, where even a tinkerer of modest abilities such as myself can experiment at modest cost and perhaps surprise even myself with the distances that can be covered with just a few milliwatts. :) This - and the 8.97 kHz 'Dreamer's Band' - is the direction I hope to take my rtl.sdr experiments. :)

Re: Microwave mixer diode substitutes
Conundrum, Tue Jun 06 2017, 08:48PM

If you want them, I have four 22 GHz Gunnplexers, also a 11 GHz module.

Maybe suitable as these have mixer diodes, also have a couple of used 1N series tunnel diodes from Tek scope manufacture.

Re: Microwave mixer diode substitutes
Sulaiman, Wed Jun 07 2017, 02:19AM

Goodness me ! .... what were you doing at those frequencies ?

(are you now practicing the dark art ?)

Re: Microwave mixer diode substitutes
Conundrum, Wed Jun 07 2017, 06:31AM

Found them in some stuff being disposed of by a security company.

Re: Microwave mixer diode substitutes
Sulaiman, Wed Jun 07 2017, 12:09PM

In the late '70's RS used to sell a doppler radar module,
I made a simple speed meter using one,
passing the mixer output to an audio amplifier allows you to hear the tones, quite interresting.
Certainly worth a brief 'play'.

P.S. used 3.7m dia dish on eBay.uk

Re: Microwave mixer diode substitutes
Proud Mary, Sun Jun 18 2017, 11:44AM

Thank you so much for your very kind offer, Andre, but I have more stuff than I could ever hope to tinker with in a single lifetime and am very pushed for space to store what I already have.

Re: Microwave mixer diode substitutes
radiotech, Mon Jul 03 2017, 08:48PM

What about a 1N21 ? Scads of them around.

This one took 5 minuets to out of the heap here.