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1500 questions
6
votes
4 answers
Testing for 'Bad' Coax
I have a lot of 'donated' coax that has been given to me with unknown provenance. I'm wondering what things I can do that can determine whether I keep it or send to the tip? Some of the things I have thought about doing are:
Physical inspection -…
Ben Short
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6
votes
2 answers
Is there a best ratio of L to C in a resonant circuit?
When designing a resonant circuit, for example as a local oscillator, the product of $L$ and $C$ determine the resonant frequency according to
$$f_{res} = \frac{1}{2\pi \sqrt{L C}}.$$
This means that we can reach a frequency of $7030 \text{ kHz}$…
DK2AX
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6
votes
2 answers
Do I need a separate SWR meter if the transceiver has one built-in?
I'm going to buy Yaesu FT-891 as my first transceiver.
I know that I can measure SWR with it if I use FM mode and minimum power, which is 5W for this transceiver. However, I don't know whether it's always safe. For instance, if I connect a…
Aleksander Alekseev - R2AUK
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6
votes
1 answer
Do short waves pass through or reflect off concrete buildings?
I live in Moscow, Russia and use DIY indoor magnetic loop antennas to listen amateur radio. Recently I received quite strong signals from Italy (20m, IV3UTV) and Slovenia (40m, S51CK), both operators are ~2000 km from me. One thing I don't quite…
Aleksander Alekseev - R2AUK
- 4,307
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- 55
6
votes
1 answer
How do PTT buttons work?
I'm really new to this, and I was wondering how the whole PTT system works? I have a headset with microphone, and a Baofeng UV-82 radio. I know the radio has its own PTT button, but is there any kind of PTT button that could be attached to it via…
Jack. D
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6
votes
3 answers
Battery capacity vs. weight for portable transceivers
What kind of battery has the most capacity for the weight? I want to take my transceiver backpacking, so I care about weight.
Timtech
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6
votes
1 answer
Are Elevated Radials Necessary for Elevated, 5/8-wave "Ground-Plane" Antennas?
Currents at the base of an elevated, 5/8-wave, vertical ground-plane (GP) transmit antenna are lower than when that vertical conductor is 1/4-wavelength. Does this mean that the performance of the elevated radials is less important in producing…
Richard Fry
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6
votes
2 answers
What happens when I and Q are switched?
In https://ham.stackexchange.com/a/1068/9 it's shown that one can use
$$ r = \sqrt{I^2+Q^2} $$
to decode AM signals from a direct conversion receiver. It appears that, in this particular case, I and Q are interchangeable, thus the SDR doesn't care…
Adam Davis
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6
votes
1 answer
How do I legally use a Baofeng UV-5R radio for communication?
I'm new to radios. Only ever used them for squad communication in airsoft. I have two Baofeng UV-5R handhelds and would like to use them this week to communicate on a family camping trip with no cell service. I wanted to know how to do this legally…
Rwstahl12
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6
votes
1 answer
Using Direwolf with multiple radios?
I'd like to play around with ax.25 connections. It seems that if I have more than one radio (operating on different frequencies) that I would want to have multiple ax.25 interfaces. Direwolf creates a /tmp/kisstnc symlink to the KISS pty device,…
larsks
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6
votes
3 answers
"Coaxial capacitors in line” in E4E04?
I've been studying the U.S. license examination question pools. For the most part, it is reasonably obvious what the questions and answers mean even when I am not yet able to come up with the answers on my own. However, the correct answer to this…
Kevin Reid AG6YO
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6
votes
1 answer
SNR measurement for a BPSK/QPSK signal
I have created a software (gnuradio) that performs modulation/demodulation and supports a number of modulation schemes and error correcting codes. I'm in the process of evaluating the BER vs SNR for this software by using a secondary…
Moses Browne Mwakyanjala
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6
votes
4 answers
Why does not a bigger antenna receive more power?
According to http://www.antenna-theory.com/basics/aperture.php, the power received by an antenna depends on the power density of the incoming wave, the wave length (which I consider to be fixed) and the antenna gain. So if I want to receive more…
Giovanni Mascellani
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6
votes
2 answers
Are old USA amateur radio licenses in the public FCC database?
My old man worked in avionics for 30+ years and taught me nearly everything I know about radios, like how a superheterodyne receiver works, how the ionosphere refracts signals, etc. He grew up only a half hour away from the ARRL headquarters, and…
durette
- 161
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6
votes
3 answers
What does a first-time operator need to know when looking for a DIY kit?
When I was growing up, I lived about three blocks from a Heathkit, and envied every device on the shelves. Now that I'm older, am teaching myself electronics and have a background in film and television broadcasting, I think I'm coming down with the…
dwwilson66
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