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10
votes
3answers
3k views

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 ...
7
votes
2answers
1k views

Dipole Antenna Current Distribution at any Time Instant

Above is a connection of half-wave dipole antenna. The book states that the current profile is same at any given time instant on both the radiators, each of quarter wavelength length. Now my ...
6
votes
1answer
568 views

Can tropospheric scatter effect be used by 802.11 links?

What are the lowest EIRP and antenna gain requirements that make possible use of troposcatter at the distances of 100 to 150 kilometers assuming conventional WiFi (6 Mbit/s data rate with OFDM/BPSK ...
5
votes
2answers
420 views

What are the requirements of the address given for a US licence?

I'm going to be visiting the US soon (I live in the UK), and since I've heard it's very easy to get a US amateur radio licence and it's something that could be beneficial, I thought, why not? I see ...
2
votes
1answer
6k views

PL-259/SO-239 vs N Type vs BNC which is best connector to use when?

I understand that the: PL-259/SO-239 connector (so-called "UHF connector") isn't great for UHF frequencies, but is very common N type connector is water-proof; and the BNC connector is quick to ...
10
votes
2answers
963 views

Why do some DX listen on a different frequency than they transmit on?

I've heard some DX indicate "CQ up 5" for instance, indicating that they are listening on a different frequency than they are transmitting on. What are the reasons one might want to do that?
5
votes
1answer
9k views

How to calculate single-stub match (general case)?

I'm trying to build a 1/2 wave "Coaxial J-Pole" antenna, similar to what is described here: Such an antenna would be great for stringing up in a tree when operating remotely, no tuner needed. The ...
5
votes
1answer
472 views

How Does the Performance of Elevated Radials Differ from That of Buried Radials?

NEC4.2 provides some information about this topic that may be of interest to some readers.
3
votes
4answers
1k views

Is it legal to broadcast an FM radio signal with a Raspberry Pi Zero?

I saw a video lately where someone soldered an antenna to a Raspberry Pi Zero and broadcasted radio signals. https://www.youtube.com/watch?v=GXedC5dQyNk&t=9s They said they were not worried to do ...
3
votes
6answers
521 views

How to make an RF probe for accurate power measurement at QRP power levels?

Typical SWR meters don't measure forward power very accurately at the lower end of the scale, which can be a real problem at QRP power levels. Better power meters like the Bird model 43 are expensive,...
2
votes
2answers
3k views

No module named 'gnuradio'

I encountered with the "No module named 'gnuradio'" error while I was trying to run GnuRadio python code in my python web server. And this is my gnuRadio generated code: ...
21
votes
10answers
94k views

What antenna on a BaoFeng UV-5R Pro will give me better reception? [closed]

I am happy with my BaoFeng UV-5R Pro but the local UHV VHF repeater and simplex reception is terrible, even for contacts less than 50 kilometers. I assume that it's because the rubber-ducky antenna on ...
18
votes
3answers
5k views

SDR sampling bandwidth - do the bits per sample matter?

I'm looking at data converter chips for a homebrew SDR design, and I see that I can choose not just the sampling frequency, but also the bits per sample. Obviously the sampling frequency has to be ...
13
votes
1answer
2k views

How would a time-difference-of-arrival receiver with two antennas know which side the signal is from?

An easy TDOA design by Byonics was published with the following schematic: It appears that the antennas are switched at a rate of 640Hz, which allows a 640Hz tone to be heard in the radio when the ...
19
votes
6answers
26k views

Using a Morse code key with a computer?

Are there standard ways to connect a hand key (straight or paddle) to a contemporary computing device (PC laptop with no parallel port, Mac, Android, iOS device, etc.) for developing or improving ones ...
18
votes
4answers
110k views

Using my Baofeng UV-5R to talk to walkie talkies

I have a few walkie talkies at home and sometimes I connect my UV-5R to them to talk to them and act as another walkie talkie. At one time, I built a little simplex repeater out of it. Should I not be ...
22
votes
2answers
13k views

What makes a 5/8 wavelength vertical desirable?

An ordinary 1/4 wavelength vertical is smaller and resonant without any loading coil or matching network. What's the advantage to a 5/8 wavelength vertical? Why 5/8 in particular, and not something ...
16
votes
2answers
20k views

How do I make a RF propagation map for a repeater?

Let's say I have a repeater. Knowing all of the information about antenna height and gain in each direction, as well as power, how can I create a map similar to this map I saw of a repeater in ...
14
votes
5answers
48k views

Good wire for wire antenna?

What properties should I look for in a good wire for building a wire antenna? Could anyone recommend something specific for me?
13
votes
2answers
15k views

What's the pinout for “Kenwood” 2.5mm TRS/3.5 mm TRS connector?

I've seen many Chinese HTs (Baofeng, Puxing, Wouxun, QuanSheng etc.) using the so-called "Kenwood connector", which has a 2.5 mm TRS connector and a 3.5 mm TRS connector. It looks something like this: ...
11
votes
6answers
2k views

Does iron ore in the ground affect my signal?

Mineral content in the ground varies from one place to another. I've visited places where the ground & waters were an orange-red shade from the high iron content; not good for trees either. This ...
9
votes
3answers
1k views

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 ...
8
votes
6answers
8k views

What is the impedance of an end-fed half-wave antenna?

It is my understanding that the feed-point impedance ($Z_a$) of an end-fed half-wave antenna is dependent on at least the following factors: $L_a$: The length of the radiating element of the antenna. ...
22
votes
2answers
4k views

Why do we use LSB below 10 MHz and USB above 10 MHz when operating SSB HF?

As a relatively new ham operator, I understand that it is customary to use lower-sideband below 10 MHz and upper-side band above 10Mhz when operating single-sideband HF. I'm curious how we got to such ...
17
votes
3answers
2k views

I hate contests. How can I avoid them?

There's nothing worse to getting home, turning on the radio, and being unable to find a clear frequency that isn't full of a bunch of meaningless QSOs where somehow everyone is 599 and no one has ...
13
votes
3answers
3k views

Is a vertical noisier than a dipole, and if so, why?

I've had people tell me, anecdotally, that a vertical is noisier than a dipole. Is this true, and if so, why? If it is true: Is this additional noise, such that SNR is degraded, or is the vertical ...
12
votes
6answers
531 views

Key CW on zero crossings - zero bandwidth?

I remember being surprised to learn that a CW signal has a bandwidth (albeit small), but when I thought it over, it made sense. Essentially, we are modulating the carrier with a low frequency square ...
11
votes
3answers
8k views

What is the effect of using different number of radials with ground plane antenna

I'm new to electronics and telecommunication at all, I having trouble with understanding the difference between 2, 3 and 4 radials, as I've searched online I've learned that I can use only 1 radial(...
11
votes
5answers
926 views

How did hams manage to tune their antennas before VSWR meters?

In the early 20th century --back when the hobby was still new-- before VSWR meters and antenna analyzers were invented, how did radio operators know whether they were tuned for maximum power out? ...
10
votes
2answers
2k views

How to do APRS in real wilderness?

I'm a relatively new ham (licensed a couple of years ago, occasional activity on 70cm and 2m, mostly repeaters). I'm looking to extend my ham experience and am interested in digital and packet modes. ...
8
votes
2answers
3k views

How does a Dual Band Handheld Antenna work?

Looking to get a (highly recommended) NAGOYA NA-771 37cm "Dual band (2M/70cm) handheld antenna" for my Baofeng UV-5R. If my math is correct - this is about a half-wavelength antenna for 70cm, but ...
8
votes
2answers
12k views

Connect two receiving antennas to the same radio

I have built a 1090 MHz ADS-B antenna roughly following some video instructions. It appears to work reasonably. However, because of how it is placed, it captures signals for more or less a half of ...
3
votes
3answers
3k views

Choke at antenna and feedpoint?

I'm planning on putting up a G5RV. From the ladder line I connect 5m coax to the shack; would it be worth doing a common mode current choke at both the antenna feedpoint and the coax feedpoint? (I ...
3
votes
3answers
2k views

Broadband antenna for SDR radio

I recently bought a very wideband SDR receiver (DX-Patrol MK4, declared covered frequencies are 100kHz-2GHz). I'm experimenting with antenna designs because unfortunately I live in an apartment ...
2
votes
3answers
6k views

Calculating bandwidth of antenna?

Is there a way to calculate bandwidth of an classical dipole antenna having this information: center frequency wire velocity wire diameter I would disregard antenna height, to simplify. I am not ...
2
votes
3answers
231 views

LSB modulation and demodulation

A USB signal is basically a baseband signal shifted up in frequency. However, an LSB signal is the mirror image of a baseband signal then shifted up in frequency. How is this 'mirroring' modulation ...
17
votes
5answers
14k views

Why do folded dipoles have greater bandwidth than ordinary resonant dipoles?

This is something I've read in passing, but never encountered an explanation of why. For example, Wikipedia says: Another common place one can see dipoles is as antennas for the FM band; these are ...
15
votes
2answers
5k views

50 Ohm coaxial cable vs 450 Ohm or 600 Ohm ladder or window line?

What are the relative advantages and disadvantages of using 50 Ohm coaxial cable as opposed to 450 Ohm or 600 Ohm ladder or window line?
15
votes
4answers
2k views

How can RF exposure hurt you?

In studying for the exam, one question came up about RF Exposure. G0A 07 What effect does transmitter duty cycle have when evaluating RF exposure? My ...
14
votes
3answers
2k views

What is a linear RF amplifier?

Most of the RF amplifiers advertised, and most of the questions about amplifiers, are "linear" amplifiers. What is a linear amplifier, and what other common amplifier type(s) exist that requires ...
12
votes
3answers
540 views

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 ...
10
votes
2answers
95 views

Where on the web can I find a calendar of upcoming contests?

For years, I have been using SM3CER Contest Service for HF contests. It is always good to have a backup, so I am looking for more or better. What do you recommend?
10
votes
1answer
2k views

Why is dynamic range relevant for an SDR?

Sometimes I see dynamic range mentioned as a figure of merit for an SDR. For example, I know that the bits per sample used by the analog to digital converter can affect the dynamic range. Why do I ...
9
votes
2answers
764 views

If two antennas of 50 Ω and 377 Ω have VSWR=1:1, then which one is more efficient?

If there are two antennas of 50 Ω and 377 Ω (same as the intrinsic impedance of air) impedance with 0 $\Omega$ ohmic resistance, and they are exactly matched with their transmission line, then which ...
9
votes
1answer
4k views

How does a slot antenna work?

How does a so-called slot antenna work? How can one construct one? What might be the radiation pattern and efficiency compared to a wire antenna? And, if a small slot antenna "works" at mobile ...
8
votes
4answers
975 views

Two Antenna Tuners in Series

My radio has an internal antenna tuner that can be activated to rapidly tune for the frequency in use. My antenna has a disgusting SWR for the band I want to use (as measured with an AA-54 antenna ...
6
votes
4answers
407 views

How can quadrature mixing adjust the phase of all frequencies by the same amount? Can it be done in the digital domain?

This came up in some feedback I got when I tried to answer What is IQ in the context of SDRs? and revealed some of my own misunderstanding. Initially, I gave an answer something like (paraphrasing): ...
6
votes
1answer
4k views

How can a quarter-wave transmission line transformer be implemented with lumped elements?

Sometimes designs call for quarter-wave sections of transmission lines. There are some situations when using actual transmission lines would not be practical: The necessary characteristic impedance ...
5
votes
3answers
266 views

Detecting signals using statistics

I have sampled a section of spectrum every few Hz. I have mean, standard deviation, and range data for every frequency sampled (and I can gather more statistics if necessary). I've sampled for ...
5
votes
2answers
5k views

What is the impedance of a 1.25 λ dipole antenna?

I would like to make a dipole antenna. This particular antenna is used for reception only; no transmission is involved. I would like to receive as much power as possible by this antenna as it is used ...

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