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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39 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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49 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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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
64 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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64 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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138 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
97 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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39 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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105 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
83 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
119 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
51 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
69 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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49 views

RIT design: math isn't adding up!

I am building a 7 MHz morse transceiver. It has a Hartley VFO and uses the capacitance of a reverse-biased diode to shift the frequency when transmitting. However, I'm struggling with this offset. ...
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1answer
543 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
60 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
52 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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67 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
75 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
98 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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1answer
564 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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77 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
343 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
222 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
994 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
85 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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33 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
341 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
694 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
89 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
117 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
79 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
54 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
128 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
397 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
261 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
706 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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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
370 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
101 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 ...
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1answer
292 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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1answer
703 views

Antenna for qrp pixie 2 [closed]

I recently set up a qrp pixie 2 transceiver i purchased from Aliexpress.I want to use it for sending morse code,and listening to the shortwave transmissions.and i want to learn more about it.so i ...
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2answers
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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1answer
391 views

QUCS simulation radio transistor amplifier

I'm trying to design a small amplifier for AM signals to use before the usual diode-C-R detection (the reception in my area is very poor). I devised a QUCS simulation as below: The diode and ...
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1answer
259 views

How to find input impedance of RA30H1317M1 RF power amplifier module?

I am building an amateur radio VHF transmitter. I want to use off the shelf transmitter module like DRA818V (or similar) as the drive amplifier and RA30H1317M1 as the final amplifier. This is my idea:...
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2answers
434 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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3answers
811 views

Identify Symbols on Circuit Diagrams for VHF Radio Build

I found these circuit diagrams for VHF transceiver online, and am having trouble recognizing a number of the symbols. Would you please help me identify the boxed symbols? Here's what I've got so far: ...
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1answer
144 views

Decreasing sensitivity of a touch paddle

I made a simple touch paddle using the circuit here. It is too sensitive and also triggers when my finger is only near one of the sides. How can I decrease sensitivity?
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2answers
664 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 ...