Most Popular
1500 questions
12
votes
3 answers
Why does "high SWR" damage transmitters, instead of "impedance mismatch"?
In the audio realm, where cable lengths are insignificant compared to the signal wavelength, I would understand an impedance mismatch damaging an amplifier as follows:
Take an audio amplifier that can deliver 100 watts of power into an 8 ohm speaker…
natevw - AF7TB
- 7,529
- 3
- 29
- 63
12
votes
1 answer
Confusion about SDR
I've just written code for the RTL2832 to receive and decode ADS-B packets (very cool!). I had some confusion about what is actually happening:
Is the raw data coming from the USB dongle literally samples of the ~1090 MHz wave? Or is the carrier…
Nathan Wong
- 223
- 1
- 4
12
votes
3 answers
What is the origin, history behind "Ben's Best Bent Wire"?
Bens Best Bent Wire
My uncle, who was a Merchant Marine in WWII used to tell me this. He was a ham, and said it would develop my fist musically.
I was a small child at the time, and through his enthusiasm for all things geeky, especially Ham Radio,…
tallship
- 171
- 1
- 8
12
votes
5 answers
What is the difference between channel & frequency & band in RF?
I am reading about wireless networks basics. I found three terms I cannot find exact definition for: channel, frequency band, frequency.
Can anyone give exact definitions for them?
ashok
- 221
- 1
- 2
- 3
12
votes
2 answers
How much RF energy do trees and branches absorb?
For the 20m - 10m and 6m bands, will having my dipoles below the tops of trees (I live in redwood forests) drastically affect the RF power out or radiation patterns of my dipoles if I can still get them at least 1/4 wavelength above the ground?
Or…
gdc
- 308
- 1
- 2
- 8
12
votes
1 answer
Why does AM have sidebands?
Why does AM have sidebands? Isn't the whole point of AM to broadcast on ONE frequency and ONLY change the amplitude?
In the picture there is only ONE frequency and the amplitude changes, so why got AM sidebands? And why can't AM work without the…
Axel H.
- 145
- 1
- 6
12
votes
3 answers
What are the relative bandwidths of the amateur bands?
While I was operating on 40 m for Field Day, I noticed a higher SWR than when I first set my antenna tuner for the band. This happened, of course, because I was in a different part of the band, but I hadn’t done enough HF operation to expect the…
Kevin Reid AG6YO
- 25,080
- 7
- 55
- 106
12
votes
4 answers
What is generally considered "too much" power for JT-65 on HF?
Recently, I have begun experimenting with JT-65A, mostly on 20 meters. I usually run about 5 watts with that mode, since I know that JT-65 is a weak-signal mode. Is that still too much power? What is generally considered excessive power on JT-65?
krzysz00 KF5SOQ
- 551
- 1
- 3
- 10
12
votes
1 answer
What do the three-letter modulation codes (emission designators) stand for?
I've seen these weird three-letter modulation codes like J3E, A3F, A1A, F3E and so on. Someone even wrote 2K40J3E or 12K5F3E. What do these codes stand for?
user
- 4,908
- 2
- 32
- 61
12
votes
5 answers
How does an antenna transform impedances along its length?
If I insert some impedance (like a loading coil, or a trap) at the base of a monopole antenna, the effect on the feedpoint impedance is easy to predict: the impedance is in series with the antenna, so whatever the feedpoint impedance was, the added…
Phil Frost - W8II
- 52,635
- 8
- 91
- 225
12
votes
5 answers
Grounding a second-story shack with an outdoor antenna
My shack is on a second story, really far away from the house ground. To run a ground from my equipment to the outside/ground is a run of at least 60-75 feet. The antenna is at least 100 feet away as well.
How do I ground this system? I cannot reach…
Jay
- 121
- 1
- 3
12
votes
4 answers
Are antennas circuits?
For an antenna to work, doesn’t charge have to flow through it? A current must be present. To me it indicates it must be a circuit, but how is a dipole a circuit?
If they are not circuits, then how does charge flow in them?
mikew
- 345
- 2
- 8
12
votes
1 answer
How do I discover APRS coverage?
I'm considering adding simple APRS transmitters to my vehicles. I'd rather just put one in and forget about it, but I understand there are areas of the US where a stronger transmitter would be required to successfully send an APRS update…
Adam Davis
- 12,295
- 2
- 51
- 111
12
votes
3 answers
When is APRS use considered commercial?
I've heard that APRS is only allowed for non-commercial use. I was thinking of a building a weather station that uploads data via APRS (so far, non-commercial). If I then include data from that weather station on a website with advertisements, is it…
Anssssss
- 263
- 1
- 8
12
votes
3 answers
Protect rig from static charge on antenna
How can I continuously discharge static from my end-fed antenna?
My Electraft K2/100's autotuner (schematics) has an SWR bridge using two 1N5711 pin diodes. These diodes get blown if any static builds up on the antenna. I've replaced them four…
Wayne Conrad KF7QGA
- 470
- 1
- 4
- 11