signal indicator

You could unbalance the pulldown loading on that buffer by 10-20% and detect that. Differential drive are the original wideband rectifier.

Probably an ordinary BFS17 would also do. RC series in front of the base, base at near zero DC via another resistive path. The BE junction rectifies some and then an LED in the collector path is lit. Very little base current will do because modern LED in the collector path at 1mA can generate light that is uncomfortably bright. It'll pulse but very fast.

It is not very elegant but less parts.

I'd hesitate to call a simple diode detector 'RF'. It's about as simple as it gets. But why is RF a black art? Logic and even opamps are so fast these days that they work well into the RF domain.

Jeroen Belleman

Skyworks has nice sampling diodes, also of the cheaper kind. Pick an LED with low Vf and it could work. Some are really bright with just a fraction of a mA. Just keep in mind that some fast diodes can go PHUT when you exceed a couple of volts reverse by too much.

It isn't. It's fun. Whenever I do RF at a client that is about the only time where I really regret getting older and retiring. There is so much to do and it seems the next generations aren't supplying enough engineers for this field.

Yeah, but "real men's RF" is discrete. Just like real cars have a clutch. Which I was really happy to have on a drive in the mountains yesterday.

BFS17 is great precisely because it's fast but not too fast. But probably a tad slow to detect 2 GHz. Ft is just about 2 GHz.

The dual doubler thing looks good, from a few hundred KHz to over 2 GHz, with 5 pF loading on each side of my diff ECL logic.

If I use a Hittite HMC987 fanout chip, I can use one of its diff ECL outputs just for the monitor LED, and I can load that as hard as I like.

That Hittite chip is $20.

I like their SMS7621. It's rated 2 volts reverse but it doesn't leak much until about 5.

I don't mind a schottky detector and than a comparator or opamp to drive the LED.

I work in time domain, picoseconds some times, but I don't think that's RF. RF, to me, is LC-tuned narrowband circuits and antennas. DC-to-10 GHz is more macho than 9.9 to 10.1 GHz.

My Audi is the first automatic I've ever owned, and I think manuals are silly now. The 6-speed dual-clutch tranny is faster and smarter than I am, and it's great on the hills here. I can manual shift it if I want, and occasionally do for engine braking, like on the crazy downhill after Donner Summit, where grannies in SUVs (and truck drivers) are smoking their brakes.

Exactly. Conquering all those instabilities, strays and parasitics fearlessly head-on. Not suitable for wimmin or gays.

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I know lots of Real Men who are afraid of the p-word: picosecond.

Some are even afraid of the n-word.

Good plan, but that mainly detects duty cycle unless the load is frequency-dependent. And, over a thousand-to-one range of frequencies, at that. Am I being unreasonable in wanting to get an indication of amplitude or frequency from a detector?

An oldschool plan: two termination resistors, one capacitor-coupled. Thermal-couple both resistors to diodes, and detect any difference in forward drop on the diodes. The only RF components are resistors and a blocking capacitor to reject DC. A humble LM324 jellybean can handle the fine details of driving an LED.

Box it up with a couple of penlight cells, and you have a low-Z RF probe.

Agreed. I'm envious sometimes of our RF colleagues who can 'tune out' some parasitic capacitance or other, or noise-match some amplifier to sub-1dB noise figures, with just a simple L-C network, while I'm struggling with wide-band analogues of the same, much harder, yet also much more interesting.

Jeroen Belleman

That's ok, you aren't relying on it being a perfect amplifier. Only to have the BE junction rectify a little and cause enough CE current to keep an LED lit. The LED won't see much of the RF. In essence the same that happens in EMI cases but where this isn't desired, where cell phone RF >1GHz rectifies itself at the first BE junction of even slow opamps and causes a demodulated signal in the output.

Nice but that's a lot of parts.

Ouch!

That is also one of my favorites. I found that when you push them past

That should work nicely but I'd try a transistor just for sports.

Time domain is usually harder and it's real RF. TDR, for example, where you can get weird kinds of reflections and you have to understand and diagnosed where they could be coming from. A slight connector or via mismatch may not even show up in a 10GHz narrowband circuit but in pulse-echo it can cause a lot of frustration.

I drove a rental car like that in Germany and it's ok. 7-speed automatic when the stick was pulled towards one side, hand-shifting when pushed to the other side, no clutch pedal. I still don't want it on ice, snow or in mud. Or when you have to rock the car out of a nasty diagonal rut with shifting rocks in there.

When I later rented a stick-shift box truck with clutch and all I was surprised nobody came out to the truck with me despite my California license. Maybe they thought if someone can speak German he knows how to drive those.

With ECL swings, about 800 mV p-p, it works better with fewer diodes:

Then an opamp to drive the LED.

It's wonderful. If it helps me sell a bunch of $1500 boxes, it's a bargain. The CML comparator ahead of it costs almost as much.

We're looking at some distributed amplifier chips in the $200-400 range, and some fast logic gates for $70 each.

Nanosecond. I saw what you did there!

So don't. Beer you can buy.

Cheers

Phil Hobbs

Time domain is usually harder and it's real RF. TDR, for example, where you can get weird kinds of reflections and you have to understand and diagnosed where they could be coming from. A slight connector or via mismatch may not even show up in a 10GHz narrowband circuit but in pulse-echo it can cause a lot of frustration.

I drove a rental car like that in Germany and it's ok. 7-speed automatic when the stick was pulled towards one side, hand-shifting when pushed to the other side, no clutch pedal. I still don't want it on ice, snow or in mud. Or when you have to rock the car out of a nasty diagonal rut with shifting rocks in there.

When I later rented a stick-shift box truck with clutch and all I was surprised nobody came out to the truck with me despite my California license. Maybe they thought if someone can speak German he knows how to drive those.

Cars and computers should do as they're damn well told. I drive a 2012 Mustang convertible that I bought new in 2017. (It got snagged in the Takata air bag recall.)