Favourite parts with off-label uses?

The old VOMs used copper oxide rectifiers! Before silicon was discovered.

It's a sin to waste garlic bread.

No, it's just on a shelf for admiration.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

Something like this?

I had a piece of test equipment that I couldn't open the shipping container, I had to wait for a really hot day to put it outside, until the pressure equalized. I bought one of these, so it was no longer temperature sensitive storage.

It doesn't look hard, a lot of people have done it. I've built the amplifier, I just need a noise diode that will give me me 20db ENR or better to feed into it. The only zeners I can easily get are 1W and above, so have big capacitance, only good for audio. I need a physically small device that will have low capacitance. That's why I started with a GHz transistor.

I've thought about trying an HSMS286 series microwave Schottky, which break down at about 4V (if the data sheet is to be believed). The literature says that devices with a sharp breakdown curve last longer - a soft curve indicates partial breakdown at the edge of the die, which leads to early failure. So I'll need to evaluate the sharpness of the breakdown to see if it's likely to last a while.

But first I'm going to crank the Vbe on this BFR93A to see where it really breaks down. If I can get it to zener on w 12v supply, that'll probably do.

I'd prefer not to need a higher supply voltage, but I might have to compromise on that. Pure zener noise (low voltage) is much lower amplitude than higher-voltage devices which have avalanche multiplication.

The only generators I have are several home made ones, and I don't have my 100-4000MHz generator complete yet. The closest thing I have to a spectrum analyser is a couple of SDRs.

Hmm, I should finish that generator :)

Clifford Heath

I have done that thing with the BFR93A many years ago and at the Weinheim VHF ham meeting there was someone who measured these homebrew things. I got 22 dB noise or sth. like that and it was flat enough for tuning filters. Not good enough to measure noise figure, both for amplitude and source impedance. The breakdown voltage of the BFR93A was 5 or 6V IIRC. I think it went to ~ 2 GHz. I used a CCS just like the charger of my HP-35 :-)

Today I would not use a "Zener" source. If you have them, spend

2 more ERAs and amplify the noise of a 50 Ohm resistor. Yes, they have a noise figure of a few dB but you know it and it's flat. More flat than a BFR93A breakdown, and much better than any Z-diode with its huge capacitance. 1K may produce more voltage noise, but @ 50 Ohms you know that the ERAs will behave.

The problem with noise filter measurements is that the bandwidth of the noise is so large and if you want to see the stop band you need lots of power. Thus, you will have large signal conditions at the output of your noise generator. Getting closer to saturation than 20 dB will damage the crest ratio / noise statistics.

The ERAs may also need more than 5V if you include the bias resistor?

good idea!

cheers, Gerhard

Oh, thanks, nice to know I'm on a right track. I basically just guessed that the BFR93A should work, not that I saw it elsewhere.

That would be good enough for my first try!

I just thought I'd use a resistor, since I have a known supply voltage. Not a good idea?

Well now it's interesting, but I have exactly the right amount of room left on this proto-PCB for two more, and I have 20 ERA-3's.

It's on a grid-punched board with assorted top-side copper strips. I used sticky-backed copper foil to make a ground plane on the back. It doesn't seem such a bad way to prototype RF circuits, given that my toner-transfer process is in recess (the new printer creates porous blacks that don't etch well).

Assuming the ERA-3 or the layout doesn't filter it, it should stay flat.

Well I could try 220R and just check it's not oscillating I guess. Otherwise 50.

Right. Not sure what that will do to the spectrum though?

I figure they want 40mA, and based on data sheet values for other voltages (from 7V up) it looks like they settle around 3.3V, so I calculated a bias resistor for 5V and was pretty close. I guess it will be more temperature sensitive than it would be with a higher supply voltage.

I'm using 0805 resistors but not series inductors, for now. Will that affect flatness (rather than just lose some gain)?

Anyhow, I'll raise it to 12V and try that before adding more ERA-3s and switching to a resistor.

Many thanks for your advice,

Clifford Heath.

Ok with 12V, 2.6mA through the BFR93A's b-e, it zeners at 5.8V.

Two stages of amplification is possibly too much - the noise is assymetrical around 0V, see this scope photo:

I guess I need to reduce gain somewhat?

I haven't investigated the spectrum yet.

They're now biassed as recommended from 12V, with 240R.

Replacing the BFR93A with 100R drops the noise to under 1mV - still visible, but will need more amplification (no oscillation visible). One more stage might be enough gain.

--
Clifford Heath 

> I figure they want 40mA, and based on data sheet values for other  
> voltages (from 7V up) it looks like they settle around 3.3V, so I  
> calculated a bias resistor for 5V and was pretty close. I guess it will  
> be more temperature sensitive than it would be with a higher supply  
> voltage. 
>  
> I'm using 0805 resistors but not series inductors, for now. Will that  
> affect flatness (rather than just lose some gain)? 
>  
> Anyhow, I'll raise it to 12V and try that before adding more ERA-3s and  
> switching to a resistor. 
>  
> Many thanks for your advice, 
>  
> Clifford Heath. 
>

No idea. But a customer of mine had some problems with the autocorrelation of pseudo-noise for ranging purposes. The measured S-curve did not look so triangle-like as it was supposed to be.

Pure resistance from high VCC is probably easier for the beginning. Use smaller R in series, it's a matter of C over the resistor vs. C from resistor to GND. You get predictability and spend VCC.

I had quite good success with home etching, it helps during the lock-down. This here is from the same double-sided Eurocard (100 * 160 mm); the foil has been made with a Kyocera color laser on Bungard pre-sensitized material. I can etch what I can print. The A3 OKI color laser I used to have previously was clearly better, but the machine was a royal pain. The bottom side is GND and unetched. No ado with alignment.

If it needs to be really precise, i.e. microwave filters, I go to a nearby print shop and have them make an offset film from my .pdf file. That increases the wall time from .pdf to soldering from 1h:30 to 3h and costs ?8.

< > < >

Both boards were made on one Eurocard.

Cheers, Gerhard

I seem to remember something about using two zeners and subtracting them to get symmetric output

Hi Cliff, I'm not at all a HF noise guy. (So listen to Gerhard and not me .:^) But the non-symmetry is typical. You might want to look at the signal as a function of the bias current. That is your 'best' knob.

How fast a 'scope do you have? Have you tried triggering on the noise (pulses) With a DSO you can average the pulses/ noise peaks and get a pseudo-spectrum... at least a guess at the max freq.

Good luck, George H.

Yeah I've done that in the audio. It helps some, but unless you match the zeners... Well symmetrical noise is over rated... no one cares much about low frequencies.

George H.

:

es:

ound 12 GHz, but they're amazingly stable.

ost in a class with relays, but 1E5 times faster.

ulators with ceramic output caps. (It's good to be able to disconnect the s upplies during bring-up, and putting the jumper between the reg and the out put cap has this additional benefit.

ails ;)

Sorry George, parametric amplifiers only momentarily grabbed my attention ages ago (when I was trying to generate 1GHz from HCMOS).

I've always found that, except maybe at microwave frequencies that keep getting higher and higher, active circuits won out.

Cheers, James Arthur

That was also done with gas discharge noise tubes, essentially thyratrons. There was also a trick of attaching a magnet to one tube to make the noise symmetric. I haven't a clue why that would work.

--

John Larkin         Highland Technology, Inc 

Science teaches us to doubt. 

  Claude Bernard

I have thought about making an oscillator from a ceramic cap and passives, but if it could be done probably someone would have done it. It could certainly be done with a pump oscillator and some diodes and stuff.

One use for nonlinear ceramic caps is to make high voltage shock lines. Put a slow pulse into a shock line and it gets faster as it propagates.

--

John Larkin         Highland Technology, Inc 

Science teaches us to doubt. 

  Claude Bernard

20 ma LED current source chips make nice MMIC current limiters in place of resistors.

20 ma Led current source chips plus optoisolators make nice protected interlock inputs to 48 or 90VDC depending on the chip, for a whopping 63 cents.

Steve

e:

te:

ples:

around 12 GHz, but they're amazingly stable.

lmost in a class with relays, but 1E5 times faster.

egulators with ceramic output caps. (It's good to be able to disconnect the supplies during bring-up, and putting the jumper between the reg and the o utput cap has this additional benefit.

emails ;)

.

No worries, I'm mostly interested for pedantic reasons. The only 'good' physics demo's of this are mechanical, AFAIK. (oh and mag amps...)

At some point I suffer from not understanding transformers well enough. (like where the LF and HF corners are.)

George H.

Newer MMICs have internal current control loops, so can be biased from a voltage source through an inductor. The control loops have various weird low frequency effects. My new GHz o/e converter circuit will only work with old-style MMICs.

The LED current limiters are cool, but most need a lot of voltage drop.

There are some self-protecting SSRs that have low drop, basically pure ohmic up to some hundreds of mA.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

Oh, good to know, it didn't seem right that the ERA-3's could be producing this on overload. it makes sens that it's typical zener behaviour.

500MHz Tek 7904, with all the nice plug-in's :). No, I haven't tried triggering on it. But the noise looks almost the same regardless of the timebase, so that's a good sign.

But I also have a HackRF and I'm not ashamed to use it as a spectrum analyser.

Clifford Heath.

We'll see how the resistor noise looks. I'm just worried that much amplification will show the noise of the first ERA3, or power supply or ambient noise that I haven't filtered or screened out.

I could easily put a tiny wire loop inductor in series after the R, at risk of coupling to the next stage and singing. That should help at GHz.

I had excellent success with toner transfer, handling 0.6mm pin-pitch parts easily, when I was using my ancient HP LJ6L. That finally died, and the replacement HP2055DN produces a porous checker-plate that's visible only under magnification. I haven't worked out how to stop it doing that, but the etchant gets through the tiny gaps, even if I use the toner transfer foil. Perhaps I'll have another go at it, I've only tried etching once (printing many times, but only one seemed good enough to etch.

I leave the back side as solid copper, just fitting jumper wires if I need a trace. If I can't route mostly single-sided, I don't make it myself.

I haven't been able to get toner transfer working since I changed toner carts. But I've dabbled with two promising variations.

1) If you lacquer-coat the PCB *then* transfer the toner, the lacquer fills in the toner's pores. The lacquer itself, meanwhile, can be easily removed with alcohol, but the toner's pores seem to stay filled.

The toner image is printed on the paper you peel off the back of adhesive labels, or in my case, backing peeled off adhesive shelf-liner paper from the one-dollar store.

2) A variation of the above is to spray the lacquer, then transfer the toner almost immediately, before the lacquer dries. The lacquer itself grabs the toner. 3) A third method is to zap the toner with acetone/alcohol mix to make the toner tacky, then stick it to the board. That always smears the traces when I try it. "Cold Toner Transfer" e.g.

Cheers, James Arthur