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2
votes
1answer
151 views

How is impedance matching related to balance and common-mode currents?

Does a good impedance match imply good balance and lack of common-mode currents? Does a poor impedance match imply poor balance and excessive common-mode currenst?
2
votes
3answers
653 views

Packet Radio at 100 miles [closed]

I am wanting to assemble a Packet Radio solution that will allow for packet radio transmission with a range of about 100 miles or better. I am not sure what band to use, what radio to use, what ...
2
votes
2answers
1k views

High data rate on HF & MF bands

Is it possible to transfer data at a high rate, like 1-2 Mbps, on 0.5 - 30 MHz? From Shannon's Theorem, with a bandwidth of just 300 kHz it is possible to reach 1.5 Mbps. I want to use these bands ...
2
votes
1answer
219 views

Preamble of a garage door opener

After detecting the transmitted signal of a garage door opener with SDR, is it correct to assume the first repeating pattern of the signal is preamble? I only see two one and zeros with equal ...
2
votes
2answers
370 views

Could I expect 12 mile range with the GXT1000VP4 radios?

I’m considering buying a Midland GXT1000VP4 radio set from amazon here: https://www.amazon.com/dp/B001WMFYH4/ref=cm_sw_r_cp_api_6BfmBbBQZ5VBY In Suburban Pennsylvania how much range could I expect ...
2
votes
5answers
791 views

What happens if an HF dipole is made longer?

Does a longer dipole (than half wavelength), for example twice as long, tuned to 50 Ω using an antenna tuner perform better than a half wavelength dipole for the same frequency?
0
votes
1answer
89 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 ...
-2
votes
5answers
398 views

For a half wave dipole antenna, what's the value of the reactances that cancel out when the antenna is resonant?

According to a few descriptions of antenna fundamentals i've read recently including that in Wikipedia and the ARRL handbook, when a half wave dipole is resonant, the inductive and capacitive ...
24
votes
3answers
35k views

Why are some 1:1 current baluns twice as complicated as others?

I would like to add a balun/choke to my dipole for the reasons outlined in Using a balun with a resonant dipole. In the spirit of continued kit and/or DIY building for my ham shack, I set out to ...
12
votes
4answers
2k views

Are antennas circuits?

For an antenna to work, doesn’t charge have to flow through it? A current must be present. To me it indicates it must be a circuit, but how is a dipole a circuit? If they are not circuits, then how ...
23
votes
8answers
47k views

How can I avoid accidentally transmitting with a Baofeng UV-5R?

I don't have $500 for a radio scanner. If I know the few (analog) frequencies that I would like to listen to, I think one can use the Baofeng UV5R (which doesn't cost much). The only problem is that ...
14
votes
2answers
3k views

If I install a G5RV in my attic how could I be certain there are not harmful levels of RF in the shack, or my kids bedroom?

I assume that anyone who has a G5RV or G5RV junior in their attic has done so with ceramic spacers, and has zigzag or dog-leg installations, or otherwise has contorted the antenna to fit up there. My ...
12
votes
4answers
939 views

What is the advantage of making an antenna resonant?

I am constructing a small loop antenna; apprx 4' diameter, will be used with an antenna tuner (mounted at the feedpoint) and 100W transmitter, and hope to use it on 20m, 40m, and maybe other bands if ...
10
votes
5answers
4k views

Grounding a second-story shack with an outdoor antenna

My shack is on a second story, really far away from the house ground. To run a ground from my equipment to the outside/ground is a run of at least 60-75 feet. The antenna is at least 100 feet away as ...
9
votes
3answers
4k views

What are the I and Q in quadrature sampling?

For some reason I've long believed that given I and Q, one corresponds to amplitude, and one to phase, so I thought that I could hold one steady and create AM, or hold the other steady and create FM. ...
9
votes
4answers
40k views

What is the difference between channel & frequency & band in RF?

I am reading about wireless networks basics. I found three terms I cannot find exact definition for: channel, frequency band, frequency. Can anyone give exact definitions for them?
20
votes
2answers
4k views

If I hear a distress call, what is the correct procedure for helping the person?

If during normal operation, I receive a mayday or pan-pan call, how should I handle this? Am I required to provide help in this situation, and what can I do to make sure I give all the assistance ...
15
votes
5answers
8k views

If I receive an SOS signal, what is the proper response?

My 5-year old son loves sending out an SOS signal using a toy Morse code generator (wired, don't worry about false alarms for real authorities). He has learned to send the SOS signal and was asking ...
10
votes
1answer
332 views

Why is the speed of light rounded to 286 Mm in calculations involving frequencies below 30MHz?

I understand that in order to make the maths simpler, frequency ($f$) is expressed in megahertz (MHz) and the velocity of propagation in free space ($c$) for frequencies above 30 MHz is expressed as ...
8
votes
4answers
36k views

FCC tracking of unlicensed FRS/GMRS transmissions

If a transceiver such as the BaoFeng UV-5R is used to transmit over FRS/GMRS frequencies (unlicensed), it is illegal in the United States due to FCC regulations that state that the power must be <0....
17
votes
1answer
24k views

How does a mag mount antenna achieve a ground plane?

I've been thinking for some time about magnet mount mobile antennas and wondering how they establish their ground plane. Consider that many mag mount antennas have some kind of protective coating on ...
13
votes
4answers
2k views

Is is possible to operate D-Star from a software-defined radio?

What is preventing a software-defined radio from transmitting the D-Star protocol?
13
votes
2answers
8k views

When is RF grounding necessary, and when is it not?

I've seen many installations, particularly at field day and also in second-floor installations, where RF grounding is ignored entirely. What are the drawbacks to this and when is it absolutely ...
12
votes
3answers
532 views

Resort FM radio station

I stayed at a resort in the U.S. recently that is located in an unpopulated area with virtually no radio reception. To fill the gap, the resort has its own FM station that can be heard only within ...
11
votes
1answer
5k views

What do the three-letter modulation codes (emission designators) stand for?

I've seen these weird three-letter modulation codes like J3E, A3F, A1A, F3E and so on. Someone even wrote 2K40J3E or 12K5F3E. What do these codes stand for?
10
votes
2answers
1k views

Multiple simultaneous tunings with SDR

I just found out about WebSDR, and I was wondering how is it possible that many listeners listen and tune to different stations simultaneously. Which components/technologies allow this, and how does ...
10
votes
2answers
855 views

What is meant by “poles” when discussing filters?

I was looking over the product page for the K3 (dreaming I know) and noticed that they offer a variety of crystal filters. Some are 5-pole and some are 8-pole, other than price, what is the ...
10
votes
3answers
8k views

Are Baofeng radios illegal in the U.S?

Having a low price budget, my search for my first ham radio to buy has led me towards Baofeng. A quick Google search on baofeng showed a lot of results that said that certain model baofeng handhelds ...
10
votes
4answers
15k views

2m or 70cm FM mobile radio for digital mode operation

Are there any 2m and/or 440cm FM mobile radios that have audio inputs for supporting digital modes, like PSK31 or SSTV? I have a Rigblaster that I use with my HF radio so I could get a mike cable and ...
9
votes
5answers
17k views

How far can a 2.4 GHz, 1 watt signal go in a rural area?

What's the approximate range achievable by a 2.4 GHz signal of 1 watt in semi-urban areas? I can see 2 km from our rooftop. Will a 2.4 GHz signal go that far, i.e. if I send WiFi signals from our ...
9
votes
3answers
13k views

How can I reduce the noise coming in from an RTL-SDR dongle?

I've recently received an RTL-SDR dongle, and I'm picking up a lot of noise that is probably coming from my PC, especially a lot of "spikes" on the 2M band. I've already started using a USB extension ...
8
votes
2answers
4k views

How far does an antenna need to be from metal to avoid problems?

Living in an apartment, I'm struggling to get good antennas set up, especially for HF. Worse yet, I'm not allowed external antennas (but am willing to try something low profile on the balcony), my ...
8
votes
3answers
2k views

Will anodizing or powder coating or wetcoating (painting) antenna elements affect performance?

I want to put up a small tower and beam on my roof, but I don’t want the aluminum to “stick out” and want it to be unnoticeable as possible. I would think black anodizing would be the best solution ...
8
votes
2answers
1k views

Moon->Earth 433MHz link achievable digital bandwidth

Let's assume we have the following situation: Transmitter on moon orbit (distance from earth ~400'000km), around 433Mhz. Transmitter power 1W, antenna gain 10dB, circular polarization. Steered to ...
7
votes
1answer
783 views

Video transmission between ATV and SSTV

I'd like to experiment with amateur video transmission in a setup halfway between ATV and SSTV. 480 lines of B&W image would be sufficient with 10 FPS, and I'm interested in both digital and ...
7
votes
1answer
2k views

What are the most common RF connectors encountered in amateur radio? [closed]

SO-239, PL-259, UHF, NMO, SMA male/female, reverse SMA, oh my! Some of these may even refer to the same thing with different names. Can someone list the most common connector types and show a picture ...
6
votes
1answer
4k views

DMR / DSTAR / P25 Software Encode / Decode

The large VHF / UHF digital voice communication modes all require the same AMBE vocoder chip from dvsinc. This surface mount chip can be aquired standalone for a relatively high price or all of the ...
6
votes
8answers
9k views

How does the length of a metal sleeve around a (shieled) coax cable affect antenna performance?

A post on http://adsbexchange.com/forums/topic/beginners-2-cantenna-easy-diy-antenna-to-improve-rangeplane-count uses a $\frac{\lambda}{4}$ sleeve made of a pop can beneath a $\frac{\lambda}{4}$ wire ...
6
votes
2answers
205 views

SSB offset determination?

Is there any algorithmic way to determine if the mixed frequency offset in an SSB SDR demodulator is wrong (too high or low), other than listening for funny sounding voices? (perhaps by checking to ...
5
votes
1answer
523 views

Help understanding the information field in an APRS-IS message

I'm looking at the raw packet data from http://aprs.fi. I see packets such as these: ...
4
votes
3answers
677 views

Is it legal to use animal noise courtesy beep?

For Thanksgiving, I changed the courtesy beep to a turkey noise on my repeater/node. Some other people did it so I thought it was fine. Someone however told me that it did not follow part 97 FCC. Is ...
3
votes
2answers
589 views

How to determine frequency and launch angle given a target skip distance?

I would like to communicate with someone 1000 miles (1600 km) away. I'm not sure how to target a specific distance. (image source) I assume it's an interrelation of the following factors: Which ...
3
votes
2answers
3k views

Choosing a wideband antenna design

On a previous question I asked about proper antenna design for wideband SDR receiver and ways to improve signal/noise ratio. Ideally the reciever has a range of 100kHz-2GHz. Keeping in mind is ...
17
votes
3answers
2k views

What is a “random wire antenna”?

Some antenna tuners claim to match any “random wire” to any HF frequency. Can one really use a random wire as a practical antenna system? From everything I have heard, the resonance of the antenna (...
16
votes
8answers
17k views

Are there any real advantages to an aftermarket NA-701 over the Baofeng stock antenna? [closed]

I have a Baofeng UV-5R HT radio that I have been using for about a month now and I really like it because it was very inexpensive and portable. It currently has the stock antenna on it and I have ...
15
votes
1answer
7k views

How do I change my registered address with the FCC?

I just moved, and I want to change my registered address with my call-sign. Is there a form or something somewhere that I can fill out? Do I have to mail it, or can I turn it in to the FCC or ...
15
votes
4answers
2k views

What should I consider when choosing a coaxial cable?

Given a middling-power rig (up to 100 W) requiring a 50 Ω antenna, a few options for the coaxial cable with a 50 Ω impedance are RG-174 RG-58A/U RG-8 RG-213 Apart from cost, what factors are ...
15
votes
3answers
2k views

Why does SSB have the hollow voice sound?

When I listen to SSB, it has the very familiar tunnel-voice sound. What properties make it sound like this? With a Carrier and an extra sideband as AM, I don't hear the tunnel-effect at all. Is there ...
13
votes
6answers
4k views

Why are vacuum tubes still used in amateur radios?

I wonder, even in this modern generation why the outdated vacuum tubes are used. In other electronic circuits they have been replaced by more efficient (and small) transistors years ago. Why they are ...
12
votes
2answers
604 views

Is there a KML or similar file that shows all of the CQ Zones?

I'm wanting to view the CQ Zones in Google Earth, and I understand that a KML file will allow me to do so. Is there a place where I can get a KML file that shows all of the CQ Zones?

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