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1answer
13 views

How much loss is there in traps, really?

I searched and couldn't find a direct answer so thought I'd ask. We all know the mantra "traps aren't good as they have losses", but how much loss are we talking about, really? Am I correct ...
5
votes
1answer
41 views

How does this quarter-wave stub balun work?

I was searching for 1:1 balun designs that would be efficient at VHF yet could easily be made from commonly available materials when I came across these two: While the design on the right seems ...
5
votes
0answers
26 views

Choice of PCB coil design for filter inductor at ca 20 to 400 MHz, 5 W

Looking at the diplexer schematic from this nice question, I realized this can completely be done in PCB-formed elements (minus the connectors). (As a kind of counter-action to the original question'...
1
vote
0answers
21 views

2GFSK digital filter bandwidth calculation

I'm working on a S2LP from ST and I am configuring the RX digital filter. I need to calculate the bandwidth of the signal which has 2GFSK modulation. Do you think the code below is correct for ...
2
votes
2answers
47 views

What kind of RFI is this?

I'm getting a lot of noise now that I have a dipole higher up. The pattern on the waterfall makes it seem man made. Could it be power line? Or is it some kind of motor? Here's a short video of the ...
1
vote
3answers
77 views

What is the name of a device used to detect noisy appliances?

I live in an apartment. I don't have control over all of the appliances but perhaps I can mitigate if I know where the noise is coming from and under what circumstances. If I'm shopping for such a ...
1
vote
0answers
39 views

Convincing kids to learn NATO alphabet

I'm trying to make learning of the NATO alphabet interesting for kids. I invite them to spell car plate numbers during vacation with their parents. So both, the kids and the parents will learn the ...
0
votes
1answer
35 views

Lightning protection for a vent stack antenna

I've seen ham radio antennas that slide over a vent stack. The usually way to connect them to the transceiver is to lay the feedline across the roof. However, the manufacturer provides instructions ...
2
votes
1answer
28 views

Baofeng UV-5RE shows wrong TXP icon

I bought a Baofeng UV-5RE of Alibaba for a little over $30. It seems to work as expected, all the menu items are consistent with the YouTube videos I watched but... the little power icon at the top of ...
0
votes
1answer
23 views

How to match transmitter to Beverage antenna

Beverage antenna consist of pair of transmission lines - one being the "antenna proper", the other ground. The antenna is being fed via open feed line ( approximately 450 Ohms ) - one side ...
3
votes
0answers
25 views

How to measure quartz crystal motional parameters using a VNA?

I want to measure quartz crystal motional parameters with a VNA, unfortunately all Google searches I've done have lead me to nothing in concrete. I know how to get an impedance curve and measure the ...
3
votes
1answer
89 views

Where to get leaded RF capacitors

Just made my first 2m/70cm diplexer. Important: I aim to be able to use this up to 50 Watts. S21 from the LP section: Having access to regular distributors such as Farnell/Element14, Mouser, Digikey,...
0
votes
0answers
11 views

R433A SAW Resonator

I have one of those wireless weather sensor things that stopped transmitting. Inside is one of those ubiquitous R433A SAW resonators that transmit on 433.92MHz. I've verified that the board it's on ...
3
votes
1answer
26 views

GNU Radio - Frequency parameter of Signal Source Block

I designed an analog FM transmitter with GNU Radio Companion in order to understand the tool better. The hardware I use is an USRP B200. The carrier was built with a Signal Source block and the ...
3
votes
1answer
42 views

How can I replace the NiMH battery in an old RigExpert AA230 Antenna Analyzer?

I have an AA-230 Pro Antenna Analyzer. Its similar about 5-10 years old with a failing battery. The battery will only hold a charge for a day or so, and only for minutes while in use. I tried: ...
8
votes
2answers
4k views

When would we ever want to use a voltage balun in ham radio?

In a world where common mode current is the enemy, and we're constantly doing what we can to avoid RF in the shack, why would we ever choose a voltage type balun over a current balun? I understand ...
3
votes
2answers
74 views

What is an expected SWR plot for a trap dipole?

I've build a trap dipole for 20/40m bands. Traps are made of a coil wound on an insulator of RG213 coax and 3 kV NP0 capacitors. The impedance measured with EU1KY antenna analyzer is following: This ...
1
vote
2answers
92 views

Wiring Cobra 29LTD CB for home use?

I'm a beginner trying to use one of my two CB radios as a "base station." The problem is that the power cable is just two wires (no connectors/12v car plug) and a 2A fuse along one. Is it ...
2
votes
1answer
74 views

Should I bother with a doublet if I can't go straight to the tuner with open wire?

I have two trees about 135 feet apart and about 55 to 65 feet tall. I have been trying to determine which kind of wire antenna to put up there. Initially I was considering either a fan dipole or ...
2
votes
1answer
161 views

What would be a good modulation scheme for communicating a single bit of information with no more than 4ms of latency?

This question has been suggested in the comments to a closed question a couple of days ago. I have nothing to do with the original question, but this aspect of the problem made me quite curious, so it ...
0
votes
1answer
49 views

How Does the Performance of an Inverted V Dipole Compare to a Linear Dipole?

The NEC4.2 comparison in the answer below shows one example, for a practical set of installation conditions.
2
votes
1answer
163 views

What would a “crystal mixer” have been in an 1960's radio telescope at 960 MHz?

In a paper cited in comments to this answer to In the 1950's how were radio-astrometric positions with portable dishes so precise they could be assigned to their dim optical counterparts (Quasars)? ...
-1
votes
4answers
95 views

Why is a half wave dipole resonant?

Is the following explanation correct ? RF energy with a wavelength equal to twice the electrical length of the dipole is applied to the feed point at the center of the half wave dipole. To understand ...
2
votes
3answers
85 views

Confusion about dipole standing waves and feed point impedance

The animation below from Wikipedia shows the standing waves of voltage and current on an ideal center fed resonant half wave dipole in free space. The red and blue curves show the change in amplitude ...
9
votes
5answers
2k views

Non-traceable radio emitters

There are various techniques for locating a radio emitter. But what are some methods to make this really difficult? There is usually a patch to every vulnerability, at least from the world where I ...
3
votes
2answers
49 views

Are circular polarized antennas on HF subject to polarization fading?

Consider the common scenario of two amateur radio operators communicating through an ionospheric channel. Typically, each station will have a linearly polarized antenna, like a dipole or a vertical. I ...
3
votes
2answers
555 views

Can left-hand and right-hand circular polarizations exist at the same time?

I read in a comment: it doesn't matter which circular polarization you choose, because they are both present, and the whole point here is to select one of them instead of receiving both and getting ...
-4
votes
0answers
41 views

BS or Not: Hybrid-Yagi : (horizontal polarization): Angled Twin Director Element Booms Are Effective for DX Antenna [closed]

Using your best knowledge about antennas and their construction and geometry, what would make the antenna below's design choices a best or worst design choice to achieve long distance (up to 140km) ...
2
votes
1answer
63 views

Would the same callsign be issued after a license has fully lasped?

My license is set to expire in a couple of days. I know there is a grace period but I'd like to know if I were to take an exam after the grace period I would be reassigned the same callsign or a new ...
1
vote
3answers
106 views

Can a receiving antenna really be “as small as you can imagine”?

I read this antenna theory statement somewhere: And, for next-step or future thoughts: a receiving antenna can be as small as you can imagine, without loss of signal to noise. Is this BS or not?
2
votes
2answers
92 views

Double Cross antenna: what's wrong with my model?

Important note: After consulting another source, I learned that the article calls for the first pair of opposing dipoles to be fed in phase, with the second pair fed in quadrature to the first pair (...
0
votes
1answer
66 views

For a center fed half wave dipole operated at resonance, are the voltage and current in phase only at the feed point?

For a center fed half wave dipole operated at resonance, the voltage and current at the feed point are in phase in time and there is zero reactance present in the impedance seen at the feed point. For ...
1
vote
1answer
78 views

How does an Airspy HF+ Discovery compare to a “real” radio?

I was looking for a secondary radio for RX only and I thought a SDR may be a better option. I read about upconverters but then I saw Airspy has a SDR with the upconverter onboard, and claims to have &...
-1
votes
1answer
129 views

Transmit data over HF signal 10,000km away [closed]

I would like to transmit trinary data (-1,0,+1) on 20-30m wave to be received 10,000km away. From Europe to US. My first thought was this: https://www.researchgate.net/figure/Burst-modulation-mode-f-...
4
votes
2answers
92 views

Why do horizontally-polarized RF waves reflect better off ground than vertically-polarized waves?

It's a well-known fact among hams who use HF frequencies that horizontally-polarized RF waves reflect better off of ground than vertically-polarized waves. This explains why ground conductivity is so ...
1
vote
3answers
121 views

Long range HF polarization

Is it possible to polarize HF signal (20-30m) at long range (thousands of km)? It was commented in my over questions that polarization is not feasible at long range. However in this article is ...
-2
votes
2answers
95 views

Can I transmit bit data over FM signal on 30m wave 10,000km away? [closed]

I am trying to understand if it's feasible to transmit -1,0,+1 data using FM on 20-30m wavelength to be received 10,000km away. From Europe to US. Ultimately I would like to create a solution which is ...
1
vote
0answers
63 views

Double Cross Dipole antenna for 437 MHz don't tune

I'm building a Double Cross Dipole antenna for 437 MHz to be used with a SDR receiver for CW cubesat. The idea is to follow this "classic" paper from Gerald Martes, KD6JDJ. I tuned every single dipole ...
1
vote
2answers
52 views

Amplified RX-only loop antennas for DX operation?

I was reading up on the different amplified loop antennas, like the W6LVP or the MLA-30. Most reviews say "great reception", or show a SDR waterfall with a lot of stations, or show a random station ...
1
vote
0answers
25 views

How to cut phasing/transformer coax in a right way?

I'm building RHCP crossed dipole for 137 MHz satellites reception (I'm using 137.5 as a central frequency). My calcs are: frequency is 137.5 MHz λ is 2.18 m one dipole leg length equals to the λ/4 so ...
0
votes
0answers
16 views

Garage door rolling code: identifying the implementation [migrated]

I'm trying to reverse engineer my garage door remote (we're having robbery problems here, so I check if it's a weak point), here's what I found, listening on 868MHz: There's a "preamble" composed of ...
5
votes
1answer
49 views

Measuring Output Impedance of an RF (HF/VHF) Active Circuit with Hobby-level Tools

Is there a simple (by simple, I mean a hobby friendly method that trades some accuracy for expense) method of measuring the "actual" output impedance of an active or "hot" RF (HF to VHF) circuit? As ...
1
vote
3answers
812 views

FM radio demodulator IC usage

An Ebay search for "fm demodulator" results in a whole slew of ICs, but even after reading their datasheets, I have no idea what I should connect where and what input signals the chips will work with. ...
0
votes
1answer
35 views

Creating a low cost ear protection/ PTT setup for hunting

I have been trying to create a low cost communication setup for when I go hunting. Using this setup the hope is to be able to talk to one another while separated without having the audio up too loud. ...
0
votes
1answer
73 views

Outdoor Terrestial Digital TV Receiver Antenna: 500-700 MHz Band, Can I Make It Work Better?

See the unconventional antenna shown below, The whole antenna is made of two mirror-imaged Alum metal stampings on either side of a 2-cm hollow 31-cm long rectangular plastic boom. The antenna top and ...
0
votes
2answers
61 views

Relative disadvantages of impedance mismatch vs. non-resonant length wire antenna

So given a choice between a non-resonant length of wire antenna center fed by 50 Ohm coax, or a resonant length of wire fed highly off-center by 50 Ohm coax, or a resonant length of wire fed by high ...
3
votes
2answers
105 views

What is the impedance of an off-center fed resonant dipole?

Given a dipole approximately 0.48 wavelengths long, such that when fed in the center the feedpoint impedance has zero reactance, how does the complex impedance change as the feedpoint is moved away ...
1
vote
2answers
58 views

Hexbeam receiving in other directions

Have a K4KIO Hexbeam up at around 20-feet on the corner of a flat metal roof pointing at 290-degrees bearing (Europe, from Sydney Australia). Currently the Hexbeam is fixed to that direction as i don'...
2
votes
4answers
238 views

Does a resonant antenna work better than a non-resonant antenna?

Some books on antenna fundamentals i've read recently say that, for a half wave resonant dipole when transmitting for example, the traveling wave of movement of charges reflected back from the ends of ...
1
vote
3answers
79 views

Practicality of SDR-based TX/RX

When it's not possible to be at the same location as a TX/RX appliance, some form of remote control is needed. There's basically two ways to TX/RX: classical radio appliance, with or without digital ...

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