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- Dave did a teardown of a plane transponder, so we talk a bit about RF (without much knowledge)
- There is a PIC16C84 on board
- Learning or relearning
- Transmits 1030 MHz, receives 1090 MHz, 140W
- We’ll ask Jeff Keyzer on the upcoming Keyzermas
- Crystal radio is basically a pin diode with long antenna.
- Dodgy wiring on 3.5kW aircon
- Coefficient of performance
- Dishy (Starlink) teardown. Discussed briefly when Joris Aerts (518) was on the show.
- Which PCB software is the best? Question posed by past guest Robert Ferenec.
- 100 Photos vs 1 Photo anecdote
- Greg Davill is doing an “Advent for circuit boards“. This had been done by Alan Yates for circuits back in 2014.
- This is also a thing for learning code, called Advent of Code. These are all based around Christmas traditions (advent calendars)
- Chris figured he’ll be doing a lot of firmware this winter and asked for advice on Twitter about it.
- Bunnie wrote an interesting article about the PCB for the Precursor phone (?) Involves past guests
- The Arecibo Telescope has failed and is down for good. The final blow may have been a small earthquake. There are multiple views.
- Dave and Chris pretty much agree on the Hyperloop
- Train bridge construction in China. That was not from @MachinePix (by Kane Hsieh) but there are lots of great onese if you follow.
- Chris is thinking about trying out the CM4. Not mentioned on the show, but Timon did a copper clad PCB breakout for it and it worked great.
- High speed signal guide from TI
- High speed getting more common? When Jay Carlson was on the show, he mentioned his intern doing a DDR3 layout easily.
Many thanks to our Patrons! You can join at Patreon.com/TheAmpHour if you’d like to join the crowd. A special thanks to our corporate sponsor Binho, who now distribute the Sensepeek PCBite.
Toby Robb says
the australian standards for wiring is the AS 3000. Circuits supplying final sub-circuits can have mixed equipment if the breaker is labelled as such. However there are limits to this and this sounds dodgy to me!
I havent got my book in front of me atm , but A/C should have a dedicated circuit IMHO.
I am a licenced electrician in NSW.
With the RF interference, could be AM interference detected by a transistor junction, or FM detected by slope demodulation if there is something that is acting as a tuned circuit that has amplitude depending on frequency, allowing the simple AM detector to demodulate it. However a lot of AM transmitters in the USA have FM translators providing the same signal on FM in addition to the AM signal, so once you know the station you can look up the FCC database and find the transmitters, the locations and the output powers, which can be rather high for AM stations, over 50kW being typical.FM much lower power, under 1kW in most cases, and the interference likely is AM, seeing as a shorter cable removed it.
Martin Hanks says
+1 on the slope comment.
You are likely receiving FM broadcasts from Sears (Willis) or Hancock. In a tuned circuit, a strong fm signal will modulate the tuned circuit, which will the be detected in a am-style mode. There are multiple FM’s on Sears, and the majority of the Hancock transmitters are in a combined antenna.
There are no AM antennas on either tower; a broadcast AM tower with any kind of performance requires ground radials that are literally in the ground, and the entire tower is energized as the radiator. You cannot do that practically on a skyscraper rooftop with so many other tenants., though it has been done. You can also mount an isolated FM antenna array to an AM tower. Many AM stations are directional via a phased by an array of antennas, sometimes as many as 8 or more hundreds of feet apart!
WVON-AM is 10k AM with a tower just 10 miles south of the loop, that might be an AM that could get into a sensitive amp. WNTD-AM 950 is close in to the loop, with 1k by day, switching to another site further away at night. The big 50kw AM sticks are west and south of you, the closest being WMVP ESPN Radio 1000 in Downer’s Grove.
But, I’d bet you’re detecting an FM from Sears… most are about 4.5kw, and at 1500′ on the east mast looking over flat Illinois that’s a killer signal.
Chris Gammell says
Any other info about the FM interfering in a tuned circuit? This is the device in question:
Martin Hanks says
Huge fan of the show, btw… you are my Monday morning train buddies.
The deep dive on slope detection is here:
I have the H4N Zoom recorder, and though I’ve never tried it in a high-rf environment, I haven’t had any RF noise issues. Your best troubleshooting path is to try to identify the station. Stations are required to announce their call letters and city of license as close to the top of the hour as they can, though this rule is has been greatly relaxed. You’re more likely to get the station’s promotional name more often, but that’s easy to Google. If it’s an AM station, it’s going to be one of the close ones.
FM Towers radiate in a torriodal pattern, and while that looks like a donut going out, there is high power node going straight down perpendicularly from the donut hole. If you’re in that “wash” you can be in trouble. I remember a community radio station that had a 200′ antenna on the side of their 2 story building. The RF coming straight down wreaked havoc on their audio gear either as detected audio or a continuous hum.
Your Zoom recorder may be picking up AM in it’s front end, either from an unbalanced connection or just leakage right into the analog section before the A/D conversion. Try a recording, and see if the offending interference is in the file. If not, your whole problem is in the headphone output stage, which might be far less shielded or balanced. I suspect the good people at Zoom spent far more of the engineering budget on the front end.
Balanced audio inputs (typically using XLR connections) use common mode rejection to fight electrical noise. The noise immunity achieved by that is very, very good. I’ve run mic level signals 150′ feet or more near very electrically dirty lighting power with pretty amazing results. If you have a faulty side of the balanced cable, you may get audio, but none of the electrical nulling of received noise.
deep dive here: http://ew.lens.unifi.it/notes/Balanced_Amplifier.pdf
Great episode, it was nice to hear Dave again after three episodes. I have two feedbacks for you guys, hope it helps.
1. Loved the segment about the iconic telescope. I think it would have been fun if you guys could have gotten into the electronics involved in it.
2. I have noticed that you guys are championing open source a lot. Have you considered talking about its impact on proprietary enterprises enabling expensive researches that has gotten us to our current technological state?
I think it would be best to talk about pros and cons.
Thank you both for all your work.
All the best