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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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51 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 ...
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53 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 ...
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1answer
104 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 ...
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1answer
63 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.: ...
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33 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 ...
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4answers
85 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 ...
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1answer
54 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 ...
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1answer
113 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 ...
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3answers
129 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 ...
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80 views

CB Radio Effects Unit. Can anyone help with a wiring puzzle?

I’m working on a small CB radio project for a friend, but am having a hard time figuring out some technical details. If anyone has any ideas on how to solve this puzzle I’d be super grateful. The ...
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1answer
87 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 ...
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2answers
58 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 ...
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125 views

Radio Waves propagation (Intuitive Understanding of Wave propagation)

I have few similar questions regarding Radio waves communication particularly FM and AM type of Radio wave communication. Please bear with the naivety of the questions. Questions: Radio waves in FM ...
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1answer
156 views

How to add a simple ESD protection to RDA5807M FM tuner antenna pin?

I am using an i2c controlled FM tuner IC (RDA5807M) in a DIY fm radio, but I am a little bit worried about ESD protection on the Antenna line (A headphone lead being used for this). Can i add standard ...
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1answer
94 views

What is the impedance looking into a length of coaxial cable that is short-circuited at the far end and a half wave-length long?

What is the impedance looking into a length of coaxial cable that is short-circuited at the far end and a half wave long? I have been told that this the the basis of what is known as a wave guide &...
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3answers
169 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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1answer
340 views

Can I replace a 101 ceramic capacitor with a close value one?

I'm kind of new to electronics and sorry if this is a bad question. I am trying to repair my father's old radio transmitter and I noticed that the PTT won't pick up your voice. I opened it up and ...
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86 views

How to connect a 4:1 balun to a a log periodic antenna?

I'm following a plan for a home made LTE/4G UHF antenna here: https://www.thingiverse.com/thing:3221812 ...because it looks to be of a very similar to design to a very expensive 4G anntenna I know ...
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2answers
121 views

How, exactly, does the 'input signal' wave(s) modify the carrier-wave of a radio signal? [closed]

I cannot find a simple (or really, not-so-simple) explanation of how mixing the high-frequency carrier wave with the lower-frequency input signal works... Is it entirely due to constructive and ...
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1answer
101 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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4answers
248 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 ...
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1answer
73 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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1answer
89 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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1answer
2k 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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2answers
79 views

Understanding Dipole vs Commercially available antennas

I'm working on a project involving RF. I have a pretty good understanding of "HAM Radio" style RF engineering, but not at a professional level. I'm trying to find a commercially available dipole ...
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1answer
101 views

What's a good ferrite material for broadband transformers in the UHF band?

I need a single hole tube shape, that I can use up around 500 MHz. I've not found anything beyond 300MHz on Magnetics Inc, Fair-Rite etc. I need a cylinder shape with single central hole, OD <7mm, ...
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73 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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1answer
77 views

Tech help with story: Will my radio signal be blocked by a mountain? [closed]

Hoping I can get some help with a technology question for my novel. My protagonist is being pursued, and they have put a tracker in his arm he cannot remove, lest it blow up and kill him. Pretty ...
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1answer
107 views

Does a pcb as patch antenna isolate itself?

I'm currently working on a prototype patch antenna for UHF. Since I'm out of copper at the moment, I used empty PCB's as base material (don't mind the PCB in between, it's only a spacer): So now my ...
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2answers
992 views

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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0answers
104 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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1answer
523 views

Triode Regenerative Receiver Circuit - room for improvement and possible errors

I've designed this radio circuit, it's made to work on the 80m and maybe 40m band. Regen is controlled using a pot in the tickler coil. Tube is ECF82, coil is air cored on a 30mm former. Will it be ...
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1answer
312 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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2answers
1k 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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3answers
91 views

Wire size question

I am trying to figure out AWG from a European/German schematic. The wire is listed as 0,3mm. (That's 0 (comma) 3mm.) I can find wire for sale in this diameter, but I need a reference to AWG. Is ...
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0answers
36 views

Using TWS-BS-6 and RWS-374-3 for analog audio transmission?

I'm really new to electronics and thought I'd build a simple walkie-talkie as a hobby and education project. A friend suggested I consider using the TWS-BS-6 and RWS-374-3 for the radio transmission ...
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2answers
423 views

3.5 MHz 2W AM vaccum tube transmitter [closed]

What do you think of my 80m band radio transmitter I designed? Originally I though about using an Armstrong oscillator, due to its simplicity and sine wavyness, but I heard that crystals are better, ...
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2answers
991 views

JFET colpitts oscillator - very unstable

I've designed, simulated and build this simple JFET colpitts oscillator and I couldn't get it to work with real parts. I didn't have BF256B jfet model so I simulated it using some generic one. The ...
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2answers
112 views

Wanting attic antenna for LF and HF receiving

I know next to nothing about antennas and am hoping someone can tell me what antenna I need to pick up ham radio and FM signals on an attic mount antenna. I will have no need to transmit. My attic ...
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1answer
124 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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2answers
95 views

Signal Strength to ADC quantisation levels

According to the excellent site of AB4OJ, the Icom 7300 in summary has a 14bit analogue to digital converter with a 1.5 volt peak to peak input (LTC2208-14). I make this to be 91.5uV per quantisation ...
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1answer
1k views

Amateur radio practice exam question about voltage drop

So the question is as follows: ...
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0answers
56 views

Why is it difficult to localize shortwave transmissions?

I have read that it is difficult to localize shortwave transmissions, but I don't understand why that is. I know that localizing the bounced transmission is obviously difficult, but when the antenna ...
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1answer
138 views

Purpose of L2,L3 & C6 in the following CW transmitter circuit

I have been trying really hard to understand the purpose of L2, L3 and C6 in this CW transmitter, especially L3 and C6. I have received many conflicting answers such as that L3 is acting as a ...
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1answer
478 views

Transmission Line open and short analysis

I have a transmission line with the following given parameters: Characteristic impedance at 50 ohms, phase as measured using VNA or PNA and frequency. (I can get S parameters as well) Other ...
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4answers
309 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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1answer
931 views

Coaxial cable for the DC-10GHZ range

I am trying to understand how to choose a coaxial cable (for my current application, I need a 50Ohm coaxial cable that works reasonably well in the DC-10GHZ range). According to the table in section "...
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0answers
54 views

Feeding an antenna with a YIG oscillator

Assume I have a YIG tuned oscillator (2-10GHZ), output power 10-20mW, and an ultra wideband antenna corresponding to this range. Is there a problem with feeding the antenna directly with the ...
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1answer
393 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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1answer
118 views

grid dip AN/PRM10: Is the normal operating distance so small?

I recently bought an AN/PRM-10 multifunction grid dip. After I replaced some electron tubes by new ones, most of the functions seem to work fine, but in the grid dip mode, I get no dip unless I place ...