If you need an amplifier, [Hans Rosenberg] has some advice. Don’t design your own; grab cheap and tiny RF amplifier modules and put them on a PCB that fits your needs. These are the grandchildren of the old mini circuits modules that were popular among hams and RF experimenters decades ago. However, these are cheap, simple, and tiny.
You only need a handful of components to make them work, and [Hans] shows you how to make the selection and what you need to think about when laying out the PC board. Check out the video below for a very detailed deep dive.
To get the best performance, the PCB layout is at least as important as the components. [Hans] shows what’s important and how to best work out what you need using some online calculators.
Using a NanoVNA and a USB spectrum analyzer, [Hans] makes some measurements on the devices using different components, which is very instructive. The measurements lined up fairly well with the theory, and you can see the effects of changing key components in the design.
[Hans] has a lot to say about RF PCB design. If you want to get into a lot of details, don’t forget to check out [Michael Ossmann’s] Supercon workshop on RF design.
I thought this is HackADay, not EEVblog Forum.
I know you only just managed to read the second sentence, but the article basically goes on to say design your own with these cheap and tiny RF amplifier modules and put them on a PCB that fits your needs.
its been very offtopic lately
Anything I would write about your comment would get me banned. Lame.
There is an ‘ArtsandCrafts’aDay article up right now.
3d printed sea cucumber lamp or something.
Also: bets on how long it takes the usual suspects to figure out what OPs name means in American parlance?
Hint: ‘Puffer jackets’ are not a thing in the USA. We look at the Brits funny when they say that.
While not called that any more (They certainly were in the 80s), Real ones are still common in places where it gets cold, and modernized “fashionable” versions exist in many women’s wardrobes pretty much everywhere in the world above roughly 42 degrees latitude.
The issue with just selecting amps based on gain and P1dB (power) is that it neglects a very important part of an amp, which never gets listed anywhere (it’s rarely a searchable feature in lists) – the amp’s active directivity, or isolation. Namely, its S12 – S21.
There are tons of amps out there that only have an active directivity of ~3 dB or so, which means it’s extremely easy to make them oscillate with a poor output match.
To clarify a bit: taking 2 amplifiers and cascading them like that with no pad (attenuator) between them is just asking for a whole heap of trouble.
Both the GALI-S66 and the GALI-74 are HBT amps, which have notoriously bad active directivity: you’ve now created basically a nearly-40 dB amp which can easily be set resonating if facing a bad output match. You put, say, a -30 dBm signal in, it becomes a +10 dBm signal out, bounces off the bad match, and appears back at the input only down a few dB – at which point it gets amplified again, bounces again, etc. etc.
https://www.microwaves101.com/encyclopedias/active-directivity-of-amplifiers
Putting an amp like that in an enclosure will make things worse because the cavity resonance can enhance the output-to-input coupling, and again, those HBT amps are so bad (even below -3 dB active directivity at some points!) it takes extremely little to set them off. This definitely isn’t theory, it happens all the time with designs with multiple cascaded HBT amps.
You definitely want at least a 2 dB pad between them, if not more.
I’ve taken apart satellite receiver LNBs and the good ones have circulators on input and often to prevent reflected signals going back through the amplifier. The circulators are three port directional couplers. There is a 50 (typically) Ohm resistor on a port that is between the outlet and inlet of the circulator thus dissipating reflections entering the outlet in the resistor instead of back into the inlet side.
I have a pretty good stock of Mini Circuits MAR-3 and MAR-6. The MAR-3 has ~12 dB gain (NF 3.7 dB) to ~2 GHz with 17.5 dB return loss on both input and output. The MAR-6 has ~18 dB gain (NF 2.6 dB) to ~2 GHz with >28 dB return loss on both input and output.
They’re very affordable and pretty easy to use with a modest amount of care in layout and decoupling for mid range UHF applications.
Circulators are great at high frequency for isolation, but they’re generally very narrowband (in terms of fractional bandwidth).
They’re not directional couplers, though – they’re non-reciprocal devices. A lot of people naively think directional couplers (which are very different from circulators) provide directional isolation (I mean… they’re called ‘directional couplers’) but that’s backwards: as a two port device, they’re reciprocal. That’s why Mini-Circuits uses the term “active directivity” for the S12+S21 of an amp. The “directional” nature of a directional coupler is that reflections off of bad matches at the coupled port don’t go to the output (they do go back to the input, though). As in: port 1 to port 2 looks the same as port 2 to port 1, but port 1 to port 3 does not look the same as port 2 to port 3. This is different than a circulator (S12 != S21).
(Can you tell I’ve had to explain this to people who say “just use a directional coupler” to fix a bad output match?)
Also, to be clear, it’s not only the gain/return loss that matters. That’s S21 and S11/S22. It’s the S12, relative to the S21. THe MAR-3/MAR-6 are both HBT amps, they’ve both got terrible active directivity.
It is a pain in the neck to find highly-directive amps in search functions, and a ton of “old standby” gain block amps which just worked are gone. Avago had a family of amps (ABA-xy563 where x indicated 3V or 5V and y was max output power, 1-4) which were great general-purpose gain block amps, with lower power and just wouldn’t oscillate at all, and when Broadcom bought them up, poof, all gone.
This explains quite a bit I’ve been confused about when trying to find parts, thanks.
I was just wanting to make a 132.4kHz circuit to try to read pet RFID tags. Is this a good method for that, or is it better to use a variable-frequency RF IC?
132kHz isn’t really RF, just use a high bandwidth op-amp.
When did 132kHz get taken out of RF frequencies?
“experimenters decades ago”… are you saying… oh yeah… I am that old now.
Thanks, Hackaday!
:-)
Yeah, me too
Universal, lol try selling that to my bike repair shop owner