Can you help me interpret this spectrum analysis noise plot?

Yeah, but you can still see garbage if there are any intermod mixes.

It doesn't take much mixing to produce inband interference. For example: (2 * Ch_6) - Ch_11 = Ch_1 (2 * 2435) - 2460 = 2410 Mhz There are plenty of other possible mixes all of which produce interference. With a 16-22 MHz wide signal, producing intermod junk on any channel is all too easy. All it takes is two STRONG inband signals and you get a third signal for free. This is fairly easy to do with outdoor systems, where one years a fairly large number of possible interference sources, many of which can be rather strong. With the limited dynamic range of the typical Wi-Fi receiver, all it takes is something that runs the receiver out of dynamic range, and mixing takes place. Mixing can also happen in the transmitter, where a strong nearby transmitter signal, goes down the antenna, mixes in the xmitter PA stage, gets amplified, and rebroadcast by the PA and antenna.

If you feel ambitious, you can see the effect with two access points, two laptops, and a spectrum analyzer or possibly signal sniffer. Set the two access points Ch 6 and Ch 11. Connect to each one with the laptops and move some streaming data. Large packet pings to the access point IP will probably also work. Watch the display on the spectrum analyzer or signal sniffer. You'll see strong signals on Ch

I haven't done this test in many years, so I don't know if todays access points are better or worse. I guess I should try it, but I'm busy (or lazy) until maybe next year.

Punch cards were for the CS weenies. ;-) The real nerds had slip-stick scabbards hanging from their belts (I carried mine with my books). Over my senior year, the slip-sticks were being replaced by calculators (and holsters for scabbards ;-). I bought an HP, and yes, it was $400 (about 10-weeks gross pay).

Here in Alabamastan we actually have a state college, The University of Auburn, which is both the premier agricultural and engineering school. I traveled to Auburn one year to visit some friends and drove past "The Swine Research Unit". The smell could gag a maggot but the pigs were happy. In the mid 1960's at The University of Alabama, I started playing with and learning a tiny bit of Basic and Fortran in order to play with the Univac which was on its way out and the new IBM 360/50 RAX system which was replacing it. Kids these days have no idea how user friendly computers are now compared to what I started playing with like the analog computer at my school but I really believe computers were more fun all those years ago. Now they're tools, not so exclusive anymore and any kids gaming computer has much more computing power than what was considered a super computer at one time. ^_^

TDD

I can't disagree with Jeff's situation, only I don't have the new ladylove. I have all the "stuff". It gets to a point where you can't find that widget you built way back in the early 80s.

That's when it gets to me!

Huh? Wow. I had never heard of that, for antennas & reflectors. Hmmm... I've seen it on the inside of monitors I've disassembled, especially the white ones (where the inside is a scratchy gray painted color).

Hmmmmm..... so what would I paint?

I guess I'd paint the backside of the Rocketdish reflector. Would I also paint the outside of the Rocket M2 radio unit? I guess I could also paint the CAT5 cable coming into the rocket.

Oooops. I just realized, I did NOT use shielded cable for my cat5. I used indoor plenum stuff. I wonder if shielded cable would have made a difference?

Oh I had a slide rule too. It was a K&E as I remember and I wish I still had it. ^_^

TDD

I'm still amazed that you saw that, lurking inside the graphs!

You must have eyes like an eagle, because I had not seen it (until you pointed it out).

Although, for the life of me, I can't determine the *source* of that channel 9 interference since nothing inside the house or nearby seems to have a strong enough signal to register as channel 9 WiFi...

For example, here is a scan on my laptop for access points:

Nothing is on channel 9.

Here is a scan of the access points from my radio:

So, I do agree with you that there is a good amount of channel

My Dad, bless his heart, taught me how to use a slide rule when I was in high school trig class. His was bamboo and white, as I remember it. He bought me a smaller one, and I cherished it. I hope I still have it, but, I've moved a half dozen times since so it's somewhere.

Hi, You guys are little bit behind me, when I was into it during and after school, computers were called electronic calculator as such containing vacuum tubes, mechanical relays.. from there transistors, small scale IC all the way into nanotech which is now. I used to use blank punch card with columms and rows all half pre-punched so we can push the confetti out to make holes where we want to do Fortran programming. If you drop the card deck by accident, you have to resort one by one to make them in proper order before you can have it read. Also remember 51 column card? Credit card receipts were 51 column card size which could be read after they are punched by key punch operators(girls) reading the amount written and imprinted account number. My Ham radio hobby was from the '50s, licensed in '60. Hold Extra U.S., Advanced/Digital Canadian, First class Korean licenses. Right now I am busy resetting up our HT system into 7.1 with new AV receiver and speakers. Better be done before X-mas.

Hi, I still have mine in a leather case on my study desk shelf.

We must pass our knowledge and skills on to a younger generation because they are being lost. If our modern society crashed, most people would be helpless because they have no idea how older simpler technology works. Perhaps Boy Scouts could help people survive? o_O

TDD

Save that forever!

I still have some 8" floppy disks!

My kids were amazed.

I'm saving them for the grandkids, but, they never saw so-called (hard sided) floppies ... so it might not make as much an impact on them.

Ditto. Despite the briefcase analog computer contrivance, the grunt work was done with a 6" K&E. The one in the photo is what I used a half century ago. (Hmm... why am I suddenly feeling old?) I still use a slide rule for doing gear ratios. I also give occasional demos of the slide rule to kids that have never seen one. Incidentally, I give a song and dance on using a nautical sextant in a few minutes... oops, I'm late.

Mine is a Post Versalog. I still have it, as well as the HP-45 that had its 40th birthday last month. ;-)

Oh man, the HP-45 cost as much back then as a desktop computer costs now. ^_^

TDD

The HP-45 was $395 in 1973 but very different dollars. About 50x different, for me.

Kind of depends where they put the AGC. Normally it is back in the chain a bit, but some designs put it further up to get lower noise.

Yeah, sorta. These daze, all the wi-fi chips are digital. The purpose of the RX AGC to make sure the input A/D converter uses all the available bits for maximum dynamic range (and lowest digital noise). Therefore the AGC stage is usually the first device after the T/R switch.

The big question is where is the detector that tells the AGC to reduce gain. Usually, it's right after the A/D converter, inside the CPU. It checks for the peak digitized signal level. If it's above some threshold, the AGC turns down the front end gain until the level is constant.

That was a heck of a lot of money for me in those days considering minimum wage was $1.60/hr and I was paying 22 cents a gallon for regular at the San-Ann gas station. In 1971 I was working at a defense plant that made some munitions parts for the military and I was paid $1.68/hr because I was working 11pm to 7am. The 8 cents was called a shift differential paid to those who worked the night shift. ^_^

The pot's been boiling for a long time and the frogs still haven't jumped out. o_O

TDD