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Microwave mixer diode substitutes

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Proud Mary

Wed May 17 2017, 11:00PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

I've been experimenting making a simple UHF impedance bridge to test out some broadband antennas I've been working on for my SDR setup. (Thumbnet N3 and NooElec NESDR SMArt running SDRsharp for anyone who's interested.)

Does anyone know any cheap substitutes for microwave mixer diodes that would be good up to 2GHz - or even 1.5GHz if that's all I could hope for - please?

I have two Russian equivalents (or so it's claimed) of the legendary 1N23 microwave mixer diode, but I don't want to commit these until I absolutely have the circuit working with everything under control so won't be putting them at risk.

All help welcome. Thank you. Stella.

Sulaiman

Thu May 18 2017, 06:22AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

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.

Proud Mary

Thu May 18 2017, 07:47AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

The BAT15 looks promising and a big cost saving!

Thank you so much! :)

Proud Mary

Thu May 18 2017, 08:49PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Sulaiman, I bought five SMD dual BAT15 for Â£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 Â£6 each!

Thanx for the heads up! :)

Sulaiman

Thu May 18 2017, 09:28PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

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 !

Proud Mary

Thu May 18 2017, 10:40PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

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 100Î¼A 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.

johnf

Fri May 19 2017, 06:59AM

Registered Member #230 Joined: Tue Feb 21 2006, 08:01PM
Location: Gracefield lower Hutt
Posts: 284

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

Sulaiman

Fri May 19 2017, 09:53AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

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

Hazmatt_(The Underdog)

Fri May 19 2017, 04:05PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

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.

Proud Mary

Fri May 19 2017, 04:37PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

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

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