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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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Guidance on development of FM radio [closed]

I am in the process of learning all about FM/AM and already have managed to make my own working transmitter. All these are some starting steps in order to make my own FM radio. Regarding that, I would ...
Gregory Kafanelis's user avatar
-2 votes
4 answers
117 views

How can an audio signal with varying frequency be modulated using FM? [closed]

An audio signal can have varying frequency and amplitude and both are the part of the information. As I understand it, frequency modulation is a technique where the frequency of the carrier wave is ...
Ritam Sarkar's user avatar
6 votes
2 answers
123 views

How accurate is the antenna reciprocity principle in practice?

The Antenna Theory book by Balanis goes through a theoretical explanation. In my real antennas (I'm an Amateur Radio operator) there are other things like transmission lines and matching circuits. I'd ...
gschro's user avatar
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2 answers
289 views

Why won't the TL084 amplify the RF output of a tank circuit?

Specifically, if a circuit can amplify a 10mV (10kHz) injected sinusoidal signal to about 6V, why does it not amplify the 10kHz RF output of a L-C tank circuit? The tank circuit below has a resonant ...
James V Stone's user avatar
-2 votes
4 answers
102 views

RF signal chain gain

In conventional electrical signal chain design, we now exactly what is the amplitude of signal in any node, from source to load. In radio frequency circuits which contains antenna. We don't know the ...
mohammadsdtmnd's user avatar
0 votes
1 answer
183 views

Grounding shortened vertical antenna with coils?

The calculated coil for 27 MHz shortened vertical antenna with the length of 5cm and 0.2 mm diameter is about 65uH. It is unrealistic with that bandwidth and efficiency, but it serves theoretical for ...
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0 votes
1 answer
258 views

Demodulation of FM signal frequency

After playing with homemade AM radios, I noticed that it is boring to broadcast AM signals all alone. I have also noticed that the AM stations around us, are so limited that I had no other chance than ...
user avatar
0 votes
1 answer
125 views

AM radio spectations - how does it work

I have captured a RF-AM transmitter circuit on internet. It is clear that the input signal will be pre-amplified and then it will begin to modulate the signal. The question is about how the circuit ...
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0 votes
1 answer
196 views

Why does SWR change with coax length for not matched transmission line and load?

I thought that even for not perfectly matched transmission line and the attached load, the SWR value will be constant and will not depend on transmission line length assuming the line is lossless. ...
andrzej's user avatar
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2 votes
1 answer
593 views

Critical approach to RF amplifier

This is a 20 MHz RF amplifier circuit below. I believe that it will work. It consists of a pre-amplifier and an emitter follower, which I had calculated once. I am complete beginner in electronics. Do ...
user avatar
0 votes
1 answer
124 views

How to increase the carrier signal voltage of RF AM modulation?

The circuit below is an example for RF modulation: Question is about carrier signal voltage of RF AM modulation. What happens when the message signal is amplified and it would have more voltage and ...
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0 votes
1 answer
108 views

Why grounding the circuit with external stuff, when a capacitor can do it?

I am examining my own radio circuit now for several days, so I included a pic: When the circuit has been powered up, it works fine without fingers or equal grounding methods, for example by getting ...
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2 votes
0 answers
195 views

How to calculate an rf amplifier stage

I changed the LC tank of the circuit below for operation in the 2m ham radio band (144-146MHz, I'm a licenced Class A Ham). Now I'd like to add an amplifier stage to increase the output by about 30dB. ...
Laurin's user avatar
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3 votes
2 answers
2k views

Understanding FM Broadcast Receiver with RDA5807FP

I've been trying to build an FM broadcast receiver for the last few weeks know, with simple designs like with LC circuits, but I've realized that an IC based radio outperforms simple transistor radios....
Charlie Nicholson's user avatar
0 votes
2 answers
168 views

Minimize Single Balanced Mixer Insertion Loss

I am self teaching RF via the internet, "Introduction to Radio Frequency Design" by Wes Hayward and the 2005 ARRL handbook. My intended project is a 1 stage IF heterodyne receiver. Not ...
Yousif Alniemi's user avatar
4 votes
1 answer
226 views

Why would the power sent in the first place for it to be reflected on say a transmitter if antenna is open, or a higher impedance antenna connected? [duplicate]

I'd really like to know in a fundamental way why power is said to be reflected during a mismatch and mainly if this is related to the maximum power transfer theorem. By that logic, if the load ...
George kirby's user avatar
2 votes
1 answer
288 views

Can I use an SDR to transmit on the ISM band without a license?

I would like to use my SDR to transmit arbitrary data. Can I freely transmit in the ISM bands without any license, as long as I abide by the regulations? My understanding is that I can transmit at up ...
Manuel Menzella's user avatar
1 vote
1 answer
1k views

Yet another 807 tube transmitter

I just can't seem to get away from these 807s. Although I am to the point where I might replace them with 6146s. I built this transmitter with a 6AG7 oscillator, and 2x 807 final amplifier. The ...
McMurdo's user avatar
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1 answer
243 views

Using a series of attenuators for a sampling HF transmission math or design errors/misunderstand/ignorance

TLDR: Why does my math not work. SITUATION: I have a 1.5KW 50 ohm RF dummy load for ham radio and I'm trying to design a sample port for monitoring with a spectrum analyzer. I have now realized that ...
Cory Lytle's user avatar
0 votes
0 answers
444 views

A DIY SWR bridge and some problems (toroids, diodes, etc.)

First of all, I've been a licensed radio amateur for 2-3 months. I want to make an SWR bridge myself that will work in the HF band. I want to use the MFJ 945E SWR bridge circuit as I don't have enough ...
Asena Güven's user avatar
1 vote
1 answer
593 views

TV tuner pinout

I was looking for some old VHF/UHF TV tuners for an RF receiver experiment and stumbled upon this old tuner from a shop. It has a label showing TELE1-030A and an IC inside shows ALP008M (Terrestrial ...
user132257's user avatar
0 votes
1 answer
106 views

Antenna tuner PCB trace impedance

I'm interested in building an antenna tuner for amateur radio HF frequencies. On the transceiver side of the tuner circuit, the impedance of the PCB traces can be matched to the 50 Ω of the ...
James's user avatar
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2 votes
1 answer
953 views

How do I match the output of a transistor amplifier to 50 Ω?

I'm working on a simple single BJT transistor amplifier to amplify the output from an oscillator for use as a CW transmitter at 7 MHz. I'm using an emitter follower to provide the power gain, and I'm ...
goblinator's user avatar
0 votes
0 answers
143 views

Faulty PNP Transistor switch fix...what is causing the noise on the base?

I built a ham radio amplifier kit that takes about 5 watts drive and makes 70 watts. It is called a MiniPA70. Here is a website someone put together describing its build/use. http://pa-11019.blogspot....
Jeffrey Edward Messikian's user avatar
0 votes
2 answers
201 views

What resistor value could I use to replace this S-Meter?

I'm designing a 40m radio. The schematic I'm using as reference uses a galvanometer ("S") for measuring the signal level. I'm trying to replace it with a sense resistor and an LM358 to read ...
Arheisel's user avatar
1 vote
2 answers
186 views

Are frontend amplifiers in RF transceivers impedance matched?

I think by now I get complex impedance, the Smith chart, and antenna matching, but I am wondering how in an RF transceiver, i.e. a radio, the amplifiers on the transmitting and the receiving end are ...
anyfoo's user avatar
  • 173
-1 votes
1 answer
205 views

How does a CAT 4 radio detector work in passive mode?

According to https://www.radiodetection.com/sites/default/files/Theory-Buried-pipe-manual-V10.pdf in passive mode a CAT 4 radio detector 'looks' for harmonics produced on the 50/60Hz mains buried ...
user avatar
2 votes
0 answers
111 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 ...
PlzBePython's user avatar
0 votes
1 answer
144 views

What is the name of this antenna?

I compared RSSI of several antennas including this one I found laying around: It performed from all angles about 10 dB better than for example the quarter wave ANT-433-CW-HD-SMA (Mouser Link). Tests ...
PlzBePython's user avatar
0 votes
2 answers
46 views

Datasheets, dimensioning questions

I have a problem reading this datasheet. This one is very weird, does 3-1.5 mean that pin is 3 mm wide, and 1.5 mm is meant to be a radius, or does it mean 1.5 mm and that that 3 means three pins? ...
Pavle Hribar's user avatar
0 votes
2 answers
139 views

Buying a variable inductor

I need a variable inductor of about 70 nH. I found one at Mouser. As you can see, it says that its inductance is 70 nH, but when I open the datasheet it says that inductance is from 9 to over 280 nH. ...
Pavle Hribar's user avatar
1 vote
1 answer
302 views

Oscillators-completely new approach

I found this link about high frequency VCOs. Although I don't work with such high frequencies, I gave it a try. So I designed this circuit: As you can see, I replaced BC547B (in previous post) ...
Pavle Hribar's user avatar
0 votes
1 answer
144 views

What kind of relay is used for high-power RF front-end applications?

My son and I are designing an RF frontend at 146MHz with a 300W amplifier on the TX side an an LNA on the RX side to be placed near an antenna feedpoint. The frontend will be inline to an existing ...
KJ7LNW's user avatar
  • 2,054
2 votes
4 answers
3k 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 ...
Pavle Hribar's user avatar
0 votes
0 answers
60 views

Estimating the range of an antenna and determining what the best option is?

I'm very new to radio communication so I apologize for the lack of knowledge about this subject. That being said, I'm looking for a directional antenna imagine a situation as follows, I'm in a rural ...
icyli2's user avatar
  • 19
0 votes
2 answers
121 views

Getting started with Radio design [closed]

For a while now, I have been exploring many RF, communication protocol and radio etc. I am kind of looking for a way where i can implement the software stack for a particular open Radio. Means like ...
Narashiman's user avatar
3 votes
1 answer
831 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 ...
Rohit Bokade's user avatar
1 vote
1 answer
93 views

Can you measure or estimate antenna reflection back into freespace caused by a freespace impedance mismatch?

Consider an antenna as a 2-port reciprocal network such that you may have S11 reflection at the feedpoint, but also S22 reflection back into freespace. S11 is well understood and measured because that ...
KJ7LNW's user avatar
  • 2,054
1 vote
2 answers
298 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 ...
KJ7LNW's user avatar
  • 2,054
1 vote
2 answers
634 views

Help with the error K2_A2 Coupling to shorted-out inductor L5 and looking for pointers for better modelling SWR

I have an RF linear amplifier kit that I am trying to better understand. The problem I am having is that my driver/transmitter is seeing a non matching impedance. To better understand the amplifier ...
Jeffrey Edward Messikian's user avatar
0 votes
0 answers
159 views

Test Input Transformer with Signal Generator

I have an RF Amplifier kit that is not working. The main problem is that the input transformer presents the radio with a high, unexpected SWR. It does amplify, so something works. The transformer is ...
Jeffrey Edward Messikian's user avatar
0 votes
1 answer
426 views

What is this binocular transformer and how do I model it in LTSPice, Have High SWR In Ham Radio

I purchased this 70 Watt Amplifier Kit and built it. Unfortunately, the kits do not come with any instructions. I have managed to find a variety of web sites where people built the amp and offered ...
Jeffrey Edward Messikian's user avatar
0 votes
1 answer
100 views

Difference between various 955 electron tubes

From the operational point of view, is there a notable difference between the following electron tubes? Jan 955 JRC 955 Jan 955 VT121 JHY 955 VT121 I'm asking broadly about the main points (e.g.: ...
MikeTeX's user avatar
  • 1,898
0 votes
0 answers
345 views

Understanding RF MOSFET Bias Circuit

A faulty in vehicle DCDC charger has fed 16V or so into a brand new radio and I'm stuck with a non-transmitting transmitter. This particular circuit has multiple amplification stages with two preamps ...
Alex Turner's user avatar
0 votes
4 answers
170 views

Building an FM transceiver

As an electronics hobbyist, I've already built a thing or two so this didn't seem like a complicated thing to do, but I was terribly mistaken. I wanted to build an FM modulated radio transceiver ...
transforman's user avatar
0 votes
1 answer
218 views

What's the maximum possible power output of this RF CATV amp?

please tell me what is the maximum possible output wattage that this RF CATV distribution amp (see below for specifications) would likely output with maximum possible input before damage? ~13 mW is ...
gene kuli's user avatar
0 votes
1 answer
587 views

Automatic Audio Source Switching

I was unable to find an answer to this question, but feel free to link any additional threads I may have missed. In my car, I have an aftermarket amp, and multiple HAM and public service radios. I ...
LevisJeanz's user avatar
0 votes
3 answers
900 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 ...
Expectator's user avatar
6 votes
1 answer
121 views

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 ...
Chipresistor122's user avatar
1 vote
2 answers
71 views

Radio Waves: Spark gaps vs general wireless radio antennas?

I was recently told by a friend who teaches college physics that "in reality radio waves are only generated when an electric current is made to move violently through a conductor". He went ...
kewardicle's user avatar