Questions tagged [ham-radio]

Ham radio (also called amateur radio) is a licensed form of radio communications for private and non-commercial use. Frequency allocations are made available specifically for ham radio and power levels allowed are typically much higher than available in unlicensed areas of the spectrum.

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7
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3answers
2k views

Why does the ionosphere reflect HF but allow VHF signals to penetrate through?

Wikipedia says: ... Unlike high frequencies (HF), the ionosphere does not usually reflect VHF waves (called skywave propagation) so transmissions are restricted to the local radio horizon less ...
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3answers
180 views

Final transistor in VOX circuit design is saturated even when no audio is supplied

Background: I have a μBITx v6 HF transceiver. It has an audio input and output, and a mechanism where the transmitter is keyed up when the ring connector (called PTT, push-to-talk) from the audio ...
5
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3answers
2k views

What determines the transmit frequency in this 555-based transmitter?

I'm a general class ham, and am just starting to do my own homebrewing. I was planning on basing a QRP transmitter off of this instructables project, seeing as I have a veritable plethora of 555 ics ...
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4answers
6k views

Can I only use a crystal earpiece for my crystal radio?

I am building a crystal radio for my science fair project, and I am having some issues. For my earpiece, I am using a telephone receiver which may be the issue. For my ground, I am using a water ...
9
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1answer
7k views

What, if anything, makes shielded loop antennas so great at rejecting local noise?

There is a folk wisdom, among amateur radio operators, that if you have a lot of noise on HF, such as in an urban location, then using a shielded magnetic loop antenna for receiving is really great ...
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2answers
83 views

Can an antenna be modeled as a 2-port passive network?

I've been using xnec2c to model antenna characteristics in Linux and the latest version is able to create a CSV by frequency of SWR, Zr/Zi, dB gain, and other metrics. I was thinking it would be neat ...
1
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1answer
298 views

Can Grid Dip Oscillator (GDO) detect WiFi, Bluetooth and NFC?

Can I use GDO to detect those waves? Can I buy one somewhere or I need to build one? I would to have digital one, that will just show the frequency of the waves.
1
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3answers
188 views

How would you combine DC power, bi-directional serial data, and an RF signal on a single 50-Ohm coax feedline?

I would like to power a remote device and communicate with it over some serial protocol on the far-end of a 50-Ohm coax feedline (RS232, i2c, SPI, etc), while at the same time sending/receiving an RF ...
0
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4answers
351 views

Different antenna lengths for different frequencies?

I just want to understand a few things which I couldn't get clarity from a lot of websites searched through google as I could see differing information. My questions : How does a single FM antenna ...