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8
votes
4answers
99 views

Practical limits to maintaining coherence in an HF channel

Lately I've been thinking about weak signal communication on HF. Very weak, like weaker than even WSPR could achieve. It would be nice if one could simply take any existing modulation and slow it ...
1
vote
3answers
45 views

Can a foreign student take a US license exam in the US and use that license in China?

The event I'm currently attending hosts Ham exams, and it's kind of likely that the student would pass on first attempt; would it make sense for him to take the exam? Can he just go home to China and ...
6
votes
2answers
38 views

Can an ultra-wideband system transfer data at high speed without precise clock synchronization?

Recently, ultra-wideband technology has been in the news again. From the Wikipedia article: UWB transmissions transmit information by generating radio energy at specific time intervals and ...
4
votes
3answers
389 views

Cheap antenna for new HF HAM

I just got a 100W HF radio and I am new at this. What is the cheapest antenna I can hook up without burning up my radio or shocking myself?
2
votes
2answers
85 views

Can a person in Portugal get an amateur radio license in another country?

In Portugal to transmit one must take a cat 3 exam then wait for 2 years to take the cat 2 exam. While this 2 years go by one cannot emit on his station. I find this rather annoying. Is there any EU ...
0
votes
1answer
78 views

Center-frequency parameter for gnuradio noise generator flowgraph

Can I add a center-frequency parameter for my noise generator flowgraph, is there a different noise source that has this parameter other than the generic noise source block?
0
votes
2answers
38 views

Local Relay with static

On our local Relay there are from time to time transmissions, where only static can be heard. Most transmissions via relay can be heard clearly. What could be the cause of this?
10
votes
7answers
819 views

Can I transmit anything inside a faraday cage?

Can I perform any transmission regardless of my license as long as I'm inside an RF sealed enclosure, such that no RF will be detectable from my transmissions off my property? I imagine the answer is ...
-1
votes
0answers
68 views

i need help from Hong Kong protester, i got a code from HK police behind the window [on hold]

i got a morse code , someone can translate for me , i come from HK. link : https://www.facebook.com/1107747729381260/videos/3027350677292028/ many thanks !
3
votes
3answers
876 views

Open Source Library for Digital Mode

I want to play a bit more with programming side of digital modes. However, a quick Google search turned up lots of software and some general explanations but no open-source library implementing such a ...
-4
votes
1answer
74 views

Wifi inside a rocket

I want to understand, as most rocket uses LAN cable and switches to communicate between stages. Is it possible to replace with WiFi? Although it's will be complex system but one idea to make each ...
3
votes
0answers
23 views

What value goes in the AX.25 PID field if the Layer 3 protocol is not defined in the standard?

I am working on space-ground networking for a Cube Satellite, and one of our candidate Layer 2 protocols is AX.25. We haven't settled on a physical layer, but it's likely to be some form of quadrature-...
5
votes
3answers
144 views

ARRL handbook as a reference for all your radio learning needs?

Looking to take up learning understanding everything from basic electronics to how today's wideband radios work, so that I can build my own radio systems (not just ham radios), and talk radio concepts ...
3
votes
1answer
59 views

Help understanding transmission loss of trivial circuit

I was trying to DIY a VHF/UHF diplexer, and got some weird readings from the VNA. By debugging I reached this trivial circuit: Which has the following frequency response: I'm trying to figure out ...
0
votes
1answer
56 views

Passive antenna system as a Wi-Fi repeater [duplicate]

I want to extend WiFi signal using a passive repeater between two isolated boxes (have to make both box wireless). Transmitter antenna from box A is placed in the gap between box A and B. In the same ...
1
vote
2answers
63 views

Beam antenna changed directivity

My Hy-Gain TH6DXX antenna has been up on a tower about 20 years, with excellent results. Suddenly, the gain of the antenna is off the side; in other words, when the boom is broadside to the ...
1
vote
1answer
48 views

New quad-band mobile receives while transmitting?

I've got a week-old TYT TH-9800, a quad-band (10/6/2/70cm) mobile, Chinese knock-off of a Yaesu HT-8900. So far, I love it -- several times the power of my HT, and a better antenna actually outside ...
4
votes
1answer
77 views

High-resolution GIS datasets of groundwave conductivity of the United States, besides the FCC?

The FCC publishes a map of estimated groundwave conductivity of the United States, but the resolution is quite low: Are there any GIS datasets that include groundwave conductivity at a higher ...
0
votes
2answers
96 views

Strong but unreadable signal received on 2m FM voice, transmitter less than 2km away. What could be the cause of the readability problem?

I conducted an experiment today using a prototype copper wire 2m dipole at a ground level base station (noted on images) and a FT2D HT with an SRH77CA antenna. I recorded my transmissions using a ...
2
votes
0answers
33 views

Demodulating ISO14443 (part of NFC) using SDR?

I'm looking for info on demodulating both sides of an ISO14443 communication using a cheap SDR, preferably an RTL-SDR (R820T2+RTL2832U). The application is passively monitoring an NFC exchange for ...
3
votes
2answers
84 views

What are the advantages for a receiver that uses an IF compared to direct conversion?

What are the advantages for a receiver that uses an IF compared to direct conversion ?
4
votes
1answer
58 views

How do I evaluate and use a toroidial core for my HF double-balanced mixer?

Last year, I planned to make a double-balanced mixer covering the entire 3-30 MHz band as an upconverter for my RTL-SDR receiver, mainly for learning RF circuits and ham radio. Naturally, it requires ...
4
votes
1answer
121 views

Does a UHF/VHF handheld transceiver kit exist?

I am a licensed ham looking for a UHF/VHF handheld transceiver kit. Unfortunately so far I was only able to find broken links, i.e. Ten-Tec used to produce exactly such a thing but they just don't ...
2
votes
1answer
101 views

EFHW works only on one band - what am I missing?

I tried to build a multiband EFHW antenna as described in articles by PA3HHO, PD7MMA, G0KYA and many others. I decided to start with a short 40/20/(15?)/10 meters version without any loading coils. ...
2
votes
2answers
87 views

Buying used tower

I'm thinking about buying a 70' self supporting tower that I can see had a little rust here and there. Besides minor rust is there anything I should ask the seller before I buy?
2
votes
1answer
60 views

How much field strength to blow out a receiver?

I was wondering what calculations would need to be performed to find out if a receiver will blow out in the given conditions. Portable AM receiver with ferrite rod antenna 200 ft away from MW antenna ...
1
vote
3answers
105 views

Does the impedance along a transmission line change when there are standing waves?

I know the characteristic impedance can't change because it's determined by the physical properties of a transmission line. But the impedance seen when there are standing waves changes along the ...
1
vote
2answers
42 views

How is frequency selection (tuning) accomplished in a direct conversion receiver?

How is frequency selection (tuning) accomplished in a direct conversion receiver ? A crystal filter can't be used is that correct ? Because there is no IF to mix with the incoming frequency band ...
2
votes
2answers
348 views

Baofeng DM-1801 DMR: Language switched to Chinese

The screen reset to Chinese characters. How do I get it back to English? I haven’t found any information on this problem.
7
votes
2answers
148 views

Do lightning rods attract or do they help prevent lightning?

I'd read that the current theory of how lightning rods protect a house, antenna tower, or other structure is by preventing lightning from striking -- that is, the sharply pointed rod lets charge ...
3
votes
4answers
84 views

Antenna testing, minimizing feed-line radiation?

Assume that one does not have access to a multi-million-dollar RF anechoic chamber. When testing an amateur radio HF or VHF antenna, how would one absolutely minimize the amount of any RF radiation ...
6
votes
4answers
789 views

What is the minimum signal strength I need to receive?

Let's say a transmitting station is using a 8W radio with a J pole antenna. The cable connecting the radio to the antenna is RG-58A/U and is 25ft long. At 144.075MHz, the attenuation of the cable is ...
7
votes
4answers
2k views

What fraction of 2x2 USA call signs are vanity calls?

I found out a while back that, as things currently stand with the FCC, if you take and pass all three license class exams in the same sitting, you get a so-called "two by two" or 2x2 call -- two ...
0
votes
2answers
51 views

How should i go about building my first transceiver?

So i want to build my very own transceiver, not looking for anything worldwide, just local but i do have a background in arduino and some electrical engineering, what tutorials would you recommend?
2
votes
2answers
61 views

resonance vs resonator in antenna

Resonance in electronic means: reactance of zero. (maybe wrongly/correctly someone's calling the minimum VSWR, the resonance of antenna! and this cause confusion) I've heard in Antenna Design for ...
2
votes
1answer
62 views

Do Buried Radials for Vertical Monopoles Need to be No Longer than the Monopole Itself?

This is a rather common belief among amateur radio operators, but is it true? A NEC analysis provides some insight on this concept.
5
votes
5answers
1k views

Does a 1/2 wavelength end-fed antenna need a good RF ground?

I was searching for DIY end-fed antenna. Some of the articles I found say that for a 1/2 wavelength end-fed I need a "small to no counterpoise" (with a lambda*0.05 m counterpoise), but some other ...
0
votes
1answer
30 views

Using dvb-t device as rtl-sdr

I am wondering if I can use that dvb-t device to listen 48-836 mhz? if it's no, why? thanks..
4
votes
3answers
85 views

Do resonant antennas actually resonate?

Do resonant antennas actually resonate (in the lumped circuit sense, exchanging stored energy between inductive and capacitive elements at a natural oscillation frequency)? If so, can this resonance ...
1
vote
1answer
62 views

Is there a practical way to triangulate a signal?

Around my location, there is an odd signal near 50.145MHz (at this moment it seems centered around 50.14735MHz but that changes as the day progresses). Other amateur radio operators in this city also ...
4
votes
2answers
176 views

How is a crossed-ellipse display generated from FSK?

What is the algorithm or circuit needed to generate a (vintage?, retro?) crossed-ellipse display from RTTY and/or 2FSK signals? (as per the (obsolete?) questions in some FCC exam pool) (assume ...
4
votes
1answer
346 views

Does an antenna tuner remove standing waves from a transmission line?

Does an antenna tuner remove standing waves from a transmission line ?
12
votes
6answers
20k views

Calculating Antenna Length on the FCC Exam vs. in Reality

I have seen the following formulas for calculating half and quarter wavelength antennas: Formula for $\frac{1}{2}$-wavelength antenna (in free space): \begin{equation} \mathrm{Length~(feet)} = \frac{...
0
votes
1answer
83 views

Locate a ball 1000 times a second

I want to locate a small ball in the air 1000 times a second. The ball is thrown from the ground and then flies in the air for 0.5 seconds until it lands. Distance from the location instrument is 1 ...
4
votes
3answers
326 views

Radials on a vertical, spread out evenly or not?

To have a groundmounted quarter wave vertical with a decent efficiency you need at least 16 radials. So normally you would spread them out on the ground evenly around the base. This would give an ...
1
vote
2answers
90 views
0
votes
0answers
34 views

Gnuradio loopback flowgraph is not working

I found the below uhd_two_tone_loopback example (which is one of the gnuradio provided examples) and I am trying to run it, it runs but I can't receive signal. EDIT: I mean when I run the program I ...
9
votes
2answers
128 views

What is the decimal in Morse Code?

The ITU's International Morse Code recommendation ITU-R M.1677-1 specifies a "Full stop (period)" as ".−.−.−", however it falls short of specifying a decimal point. Even the examples, though they ...
1
vote
1answer
125 views

Digital Modes Transmission Traffic Comparisons

I am looking for data that compares the number of transmissions per month or year among the various digital modes such as DMR, D-star and Fusion. I want to see how popular these technologies have ...
5
votes
1answer
112 views

UK Foundation Licence holder use of kits

The terms of the foundation licence allow for use of Commercial radios and kits that conform to IR2028. IR2028 basically says that the kits must operate within amateur bands . I cannot find any kit ...

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