EMI problems

I think you mean monopole antenna, but I get the idea. Please note that I'm not suggesting that lifting the shield be a part of design. Not only can it cause other problems, but production would probably shoot it down as difficult to build and easy to do wrong. What it's good for is testing for ground loops. On some connectors (phono, PL259), I can simply retract the plug until the shield disconnects, eliminating the need for a special cable or adapter.

I have a collection of 1:1 RF transformers, which is another way to eliminate or test for ground loops.

I sorta cheated with my examples of web articles indicating that grounding one end of the shield was proper practice. Those were mostly about CAT5, which is a bundle of twisted pairs, surrounded by a shield. Grounding one end there works because the shield is NOT part of the signal path. In ordinary coax cable, the shield is part of the conduction path, and needs to be intact.

I would say it's only a bad idea and that it does have its uses.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Use a clamp-on ammeter for 60 Hz, or some sort of CT for higher frequencies.

I vote for "always terrible."

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Well, your spectrum analyzer shows 9 mv rms into 50 ohms, which is: P = E^2/R P = (9*10^-3)^2 / 50 = P = 1.62 microwatts Ummm... I think you'll need a bigger antenna.

That's fine as long as you don't require the EMI or RFI for the circuit to operate.

Sigh. All my various spectrum analyzers are ancient. None of them are FFT type. None of them have any kind of storage. I'm looking for something better, but have some other priority purchases to deal with first. Incidentally, the IFR-1500 in the picture has a really awful power supply.

Yes. Cookies must be sacrificed in order for the can to resonate. If you left the cookies inside the can while sweeping, it will lower the cavity Q making it more difficult to see the dip or peak in the trace.

I have a confession to make. I spend far too much time on fun diversions, academic exercises, and pursuing oddities, than I should. It's a bad case of arrested growth, where I've never really outgrown my childhood curiosity. While this had provided considerable entertainment and education values, it tended to greatly irritate my former employers. The standard line was "Am I paying you to do this"?

Notice that tracking generators produce sine waves. As I recall, you don't do sine waves.

The tracking generator appears to be a hardware option on the IFR

2399c. I couldn't find block diagrams or theory of operation for the 2399C or other FFT spectrum analyzer to see how it's done. The Rigol DSA815-TG, 832, and 875 all are FFT SA's with built in tracking generators. No block diagrams for those found. Well, I did find this photo of the DSA815-TG. Tracking generator is at bottom. but that doesn't count as a block diagram.

My guess(tm) is that the tracking generator starts at some frequency. The SA saves the highest value in the FFT bin that corresponds to that frequency. The bin values are saved and the frequency is incremented to land in the next higher bin. Repeat about 1000 times, and you should have a continuous trace.

However, if you don't like sine waves, there are other ways to generate a frequency response curve. A noise generator works quite well: Record an FFT trace, average over the previous 1000 or so measurements, and you get a nice looking line instead of a noisy mess. I didn't want to invest in a tracking generator, so I went for a cheap eBay noise generator:

I can also get a frequency sweep without a spectrum analyzer using a sweep generator, RF detector, DC amp, and an oscilloscope. The pile of HP8620, and the white Wavetek on the shelf are example.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Certainly. But a high-Q resonant antenna can do some serious coupling.

A good LED is visible in office light at 1 uA, which is around 2 uW.

It's impressive how many apparent product failures, or goofy poinless experiments, turn out to be valuable later on.

But my customer does, in his specs, so I have to humor them.

We do make a few arbitrary waveform generators that can be dumbed down to make sine waves. This one makes 1 MHz with about -50 dB THD, not bad for a signal generator.

A custom lowpass filter improves that by about 80 dB, so we're about

-130 on harmonics to test our photodiode amp.

We have it.

I couldn't find block diagrams or theory of operation for the

Sweeping the tracking gen must slow down the scan, unless it sweeps in big jumps. I could try that and see if it's so.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Sure, but it doesn't need to resonant. Aim a big dish antenna, with a broadband feed (waveguide beyond cutoff, LPDA, bow tie, etc) at Mt Sutro and see what comes out the coax. I have the Mt Sutro RF exposure data buried somewhere and can probably calculate the field strength from some of the transmitters at your location. However, it's Sunday, I'm overheated, and quite sober, which means I don't have a handy excuse if I mangle the calculations. How far away from Mt Sutro are your old and new offices?

I didn't know they were that good. Impedance of the LED would be around: P = I^2 * R 2uW =1uA^2 * R R = 2/1 = 2 ohms So the fun part will be transforming the inpedance from a 75 ohm antenna to 2 ohms. 37.5:1 transformations are possible but not fun.

Incidentally, we've been here before in 2012, except that you were planning to do it using the AM broadcast band:

Yep. I've designed 3 products, at 3 different companies, where everyone within criticism range announced that it was a dumb idea, nobody would pay for it, it's a waste of time, and so on. I didn't keep track of the reasons they should have failed. All of them eventually had a very successful product run and lifetime. Nobody ever thanked me.

Lesson learned: Don't tread on managements toes.

I haven't seen one in action or found the block diagram so I don't know how it works. If it's anything like using an RF sweeper and spectrum analyzer connected with no sweep synchronization, it's going to be really slow. Since the two sweeps are at different rates, the only time anything appears above the baseline is when the generator and SA frequencies just happen to coincide. With a short persistence SA screen, it's hard to see anything. Doing the same with a storage scope, DSO display, or an HP8750A "storage normalizer" should produce usable sweeps.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

A resonant antenna can be a lot smaller than a plain one, but in the FM band I can do a 1/4 or 1/2 wave, and make it broader band to slurp up more stations.

Aim a big dish antenna, with a

I had in mind a bit of wire, not a giant structure!

I have the Mt Sutro RF

Current, 2.2 miles. New will be 2.5.

I'd need a rectifier that can deliver a few uA into maybe 2 volts. The gross load impedance is ballpark 1 meg. So I need a step-up, not down.

No rush.

I suppose a smooth or stepped sweep through each of successive FFT windows would work.

But sine waves are boring.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

The receiver antenna capture area is proportional to the square of the wavelength. The capture area is sometimes illustrated as an ellipse about 1/2 x 1/4 wavelengths, with a half wave dipole in the middle.

The captured power [W] thus increases rapidly at longer wavelengths as

expect to get much larger power levels from an AM transmitter than an FM transmitter with some distance and power.

The capture area of an electrically short (much less than 1/2 wavelengths) dipole is nearly as good as full size dipole. The problem with very short dipoles is that it is reactive (huge capacitive reactance). You can only extract power from the resistive part of the impedance, not the reactive part.

Loading coils can be used to generate inductive reactance and hence cancel the antenna capacitive reactance (conjugate match). Thus, for best power extraction, the antenna elements do not have to be resonant, but the antenna _system_ (antenna+loading coil) must be resonant. The problem is that if you need a large resistance or reactive change, the network is quite narrow band.

In addition, a random wire longer than 1/2 wavelength doesn't increase extracted power, since any voltage induced into half wave sections tend to cancel, so on FM band a random wire longer than 150 cm is not of much use.

Of course yagis etc. can be used, but they tend to be directional. The directivity is good thing, if there is only a single transmit tower at line of sight, but a bad thing, if you want to capture power from multiple towers or from (indoor) reflections.

They generally have strongly lobed patterns, though, so you'll get more signal if you wiggle them around to maximize it.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

Empty Altoids tins also work and have an iconic design language. In this case the connectors work best on the side.

Altoids jelly bean mixer

Thank you,

--
Don, KB7RPU