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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1 answer
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Amateur radio practice exam question about voltage drop

So the question is as follows: ...
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13 votes
2 answers
27k views

Why do some radio antennas require a path to ground and some do not?

I'm currently learning the basics of radio and have noticed that some radios, such as crystal radios, have a monopole antenna that is essentially a wire buried in the ground. However, other radios, ...
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12 votes
6 answers
819 views

Getting started in Ham radio

It's been quite a while since I heard about amateur (ham) radio. I think it's a good hobby to dabble into to develop an understanding of communication technology and electronics. But whatever research ...
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10 votes
3 answers
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Are there any open / unrestricted radio frequencies that are free for any use?

The only 'free radio frequency' that I could think of are the HAM radio bands. But they really aren't free, for they are regulated by laws that require you to hold a license, restrict what purpose you ...
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10 votes
4 answers
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Why can a feedline be cut randomly when the antenna needs a specific length?

With a mobile two-way radio you have the radio, an antenna mount kit and the actual whip antenna. The antenna needs to be trimed to the correct length so to match the freequency you are Tx/Rx on. ...
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9 votes
1 answer
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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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8 votes
9 answers
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Does there exist an internet-like peer-to-peer packet radio system?

Has anyone designed a peer-to-peer communications networks system, which works almost like the internet, but wirelessly? I mean a system, which: you can connect the transmitter to an usb port and ...
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7 votes
4 answers
3k views

Why would I use a transformer instead of one inductor in a crystal set?

I'm reading up on A Simple Radio Receiver. I have a question about this image: The signal from the antenna (perhaps a few tens of microvolts, or hundreds for a nearby transmitting station) is ...
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7 votes
2 answers
2k views

Tube transmitter tuning

I am trying to tune/tweak/repair this transmitter for a friend of mine. It is oscillating, and it has rf power on the antenna, but it just doesn't seem as "strong" as it should be. The diagram says ...
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7 votes
3 answers
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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6 votes
1 answer
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Ham Transceiver to computer Interface design question

I am building a Ham transceiver to computer interface, which has the RS232 port controlling the PTT on the radio. The circuit currently calls out for a 1.2K resistor in series with the RTS line and ...
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5 votes
2 answers
479 views

What is the purpose of diodes after RF power amplifier and before LPF?

I am planning to build an RF transmitter using an integrated PA module (RA30H1317M1). While studying schematics of similar transceivers, for example IC-2200H (that also has a PA module) I see all ...
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5 votes
3 answers
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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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5 votes
1 answer
393 views

BJT Clapp Oscilator for 3-6MHz

I designed a Clapp VFO to aid in my Ham Radio projects (Non-superhet SSB and CW recievers for 80M and hopefuly 40M). I chose the clapp topology for it's frequency stability. I want it to tune at least ...
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5 votes
1 answer
924 views

What is the best radio protocol for long range serial communication? [closed]

I'm working on a project that would require up to near time (<=5mins) of packet base communication over Long Distances of upwards to 80 Gm. Obviously the base station would have to be scaled for ...
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5 votes
3 answers
5k views

How to build cheap radio propagation beacon?

I want to build a Radio Propagation Beacon but I would like to find an integrated circuit that does most or all of the work of the transmitter. Transmit to 28Mhz (Ham 10-meter band) Allow me to feed ...
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4 votes
5 answers
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Does CW or SSB consume more power?

CW pumps out the full carrier but has a better SNR. On the other hand SSB suppresses the carrier, and one side-band but this suppression demands additional circuitry. There are probably additional ...
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4 votes
3 answers
514 views

Why is speech malformed when listening to a USB signal with an LSB receiver?

When you listen to an LSB (Lower Side Band) signal with your radio set to USB (Upper Side Band) or vice versa, the speech you hear is malformed. What causes this behaviour?
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4 votes
3 answers
37k views

How do I estimate the transmission distance of a 50 watt 2m radio?

Can anyone point me to a reference for calculating (estimating) the transmission distance of a 50-watt, 2-meter radio? The transmitting antenna will probably be 5-7 meters above ground. Probably the ...
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4 votes
1 answer
366 views

How does this oscillator work?

I am trying to understand the following oscillator from a Cyclone 40 transceiver (http://www.4sqrp.com/cyclone.php). Here the the VFO (in the actual device, the inductor has a bolt through it to tune ...
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4 votes
4 answers
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How should I test a coaxial cable?

I'm a ham radio operator, but haven't been very active on HF bands for a while. I have an inverted-V antenna and a long run (approximately 25m) of coax that runs from my upstairs "shack" down the ...
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4 votes
4 answers
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Duplexer for portable VHF repeater

For my undergrad EE capstone project I'm designing and building a 2m band analog amateur radio repeater. Our design goal is to build a solar-powered low power repeater (something like 5-20 watts) ...
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4 votes
1 answer
490 views

Skew planar wheel antenna - is it circularly polarised or not?

'Skew planar wheel' antennas are popular for uhf. They are often described as circularly polarised, but I don't see how they would be. Are they instead just a mixed polarisation omnidirectional ...
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4 votes
1 answer
99 views

Building a personal RF anechoic chamber in a large walk-in closet?

What would one need (besides many foam absorbers) to build an in-home small anechoic chamber for transmissions in the UHF to L-bands (specifically 500Mhz - 2 Ghz), and what resources would you point ...
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4 votes
1 answer
349 views

Arduino+2X12 LCD to emulate a defective Kenwood HF rig display unit

I have an HF rig with a bad display init (LC7582A driver and custom LCD with 9 seven-segment numeric indicators and some icons making for a total of a 100 or so segments). The input pins of the LCD ...
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3 votes
3 answers
3k views

Reverse engeneering a home automation RF 315Mhz transimtter

I have this remote control and transmitter and I want to reverse engineer the 2 RF signals sent by the transmitter. This is the board. The board says "ak-rk01se". I can also open up the transmitter ...
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  • 133
3 votes
5 answers
1k views

Troubleshoot Crystal Radio

Alright, I'm totally confused. I have built the following circuit with absolutely no result, not even a click. Even after reading through several other similar questions on the board, I haven't ...
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3 votes
1 answer
424 views

Is it possible to use a YIG tuned filter to make a YIG tuned oscillator?

My application requires an oscillator continuously tunable between 1GHZ and 10GHZ (or a wider range). The output (somewhere between 1mW-15mW) has to be coupled to an ultrawide band antenna. No PLL ...
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3 votes
1 answer
3k views

How to DIY BaoFeng radio-to-soundcard cable?

I've got a cheopo BaoFeng UV-5RE that I'd like to try as packet radio. I've snipped the plug off of the headset that came with the handheld, soldered it onto some breadboard cables, and did the same ...
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3 votes
3 answers
698 views

Frequency Synthesis from 1MHz to 800MHz

I've been trying to plan out a new project for a while. It's a wideband antenna anaylyzer for radio applications. I've figured out most of the details, but the most important part - the frequency ...
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3 votes
0 answers
150 views

RFI protection for a stepper motor controller

I'm building a remote tuning device for a magnetic loop antenna. It will use a stepper motor to turn the shaft on the mag loop's variable capacitor. The electronics will consist primarily of a ...
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2 votes
4 answers
2k views

Why does this transistor oscillator not work at 100 MHz?

I tried to simulate this oscillator in Multisim, but it doesn't work, I get just DC voltage from it. With the same biasing I got to make it work, but on lower frequency (around 1 MHz), while I want to ...
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2 votes
1 answer
148 views

Amateur radio practice exam question

The question is as follows: An interfering signal from a transmitter is found to have a frequency of 57 MHz (TV Channel 2 is 54 - 60 MHz). This signal could be the: And the options are as follows: ...
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2 votes
4 answers
4k views

Designing a simple CW transmitter/receiver

I'm interested in building my own radios for use on the air. I'm still rather new to electronics so I'm looking for simpler projects that I can build to learn on the way, and I'm thinking that a CW ...
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2 votes
2 answers
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Tube Transmitter Issues

I'm back working on my friend's 807 tube transmitter. I've had some previous posts on this and I'd like to thank all the people who responded for your help! I bought an oscilloscope and a dummy load ...
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2 votes
1 answer
358 views

an/prm-10 grid dip question - how the voltage can be negative at the grid? [duplicate]

I am trying to repair a recently bought AN/PRM-10 grid dip. I have replaced some electron tubes by new ones and (almost?) everything seems to be OK regarding the voltages at the pins of the electron ...
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  • 1,712
2 votes
4 answers
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 ...
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2 votes
1 answer
281 views

RF PCBs on 2 layer FR4

I deigning a PCB for an open-source RadioSonde with 403Mhz transmissions using Si4063 ic. Now, these radiosondes are supposed to be inexpensive since there is quite tough competition in the market ...
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2 votes
2 answers
1k views

Determining Power in a VSWR Bridge

I have recently been trying to build an Arduino based VSWR bridge. The final goal is to make it feature rich but right now im having trouble calculating the forward and reverse voltage from the ADC ...
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2 votes
1 answer
1k views

Buffer between high pass and low pass filter when making a bandpass filter?

For a passive filter stage, I want to combine a high pass filter with a low pass filter to create a bandbass filter. Can I just make a simple RC circuit for each and connect them together? Or would we ...
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2 votes
2 answers
213 views

Two signals alternately on the left and right of a frequency

I was listening to the WebSDR of Twente University, just outside the amateur band, and saw these signals. The x axis is frequency in kilohertz, the y axis is time, where the whole axis shown is about ...
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2 votes
1 answer
140 views

L-C-L vs Pi network

I am playing with a simple high-pass phase shifter implemented as a Pi network in Sonnet Lite with a center of 146MHz and discovered something by accident that I would like to understand: By mistake, ...
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2 votes
1 answer
133 views

What to look for when selecting an RF detector diode

I'm currently diving into the topic of RF detectors and I ask myself which are the key criteria when choosing a diode for a given frequency range. I have a simple detector using a 1N916, which works ...
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2 votes
2 answers
990 views

Turn on transistor with output from sound card

I want to turn on a transistor by playing sound through my computer's soundcard. I thought that this simple circuit with a diode to rectify the AC, capacitor to smooth it out, and a transistor to ...
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2 votes
1 answer
164 views

Does this crystal circuit work?

I need a tiny oscillator circuit for testing an application. Now I haven't much experience in creating oscillators so I would like to use this Collpits-circuit: I only need the carrier wave so I ...
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2 votes
0 answers
75 views

Why 7 dB power increase after combining identical strength signals?

I have signals from two transmitters that are combined via a power combiner (link). Both signals are at 7 dBm when fed into the combiner on their own. When combining both, the meter either reads 7 dBm ...
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2 votes
1 answer
3k views

Help with PTT circuit for icom radio

I'm trying to set up an APRS station using an old icom HT. Receiving is fine, but I'm having some trouble with the transmission side. When I connect all my parts together, the transmit light ...
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  • 614
1 vote
3 answers
263 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 ...
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  • 902
1 vote
5 answers
416 views

Can I combine a PLL and a DDS?

I need a controllable frequency for use in a radio transceiver with a range of 3–50MHz (i.e., 80m–6m). The frequency needs to be selectable using a microcontroller. Because chips like the Si5351 tend ...
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1 vote
1 answer
106 views

What causes 100Hz spuriour emissions on AD9850 WSPR transmitter?

I've built WSPR transmitter based on AD9850. AD9850 is driven by 125 MHz crystal. TX frequency is 14 Mhz. On the receive side there is upconverter (+125 MHZ crystal) and SDR (both RTL-SDR and AirSpy). ...
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