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17
votes
2answers
2k views

Why do repeaters use cavity filters?

Repeaters apparently often use large, expensive cavity filters to connect the receiver and transmitter to the same antenna. Why aren't typical electrical circuits, such as inductors and capacitors ...
2
votes
1answer
110 views

Preferred signal report format for Digital Voice?

When using FreeDV or other digital voice modes, what's the preferred signal report? The software has a single SNR number, but that fluctuates quickly. Since it's a digital mode, you either get the ...
5
votes
1answer
211 views

How to obtain raw data for Global Real Time foF2 Map

Note!!!!: I am not looking for help with how make a map using Google Maps API (that part is done). I need help with finding data. I am building a shortwave radio/HF listening log book online, and it ...
5
votes
1answer
816 views

What makes a good emergency-capable QRP rig for travel?

It's wintertime, which drives the concept of emergency preparedness here above the 45th Parallel. Am emergency-capable QRP rig is an excellent item to stuff into one's Go Bag or vacation gear, always ...
19
votes
3answers
692 views

What makes cellphone transmissions so energy cheap?

The modern cellphone can carry on a full duplex conversation for a time period measured in hours on a battery half the size of my handheld transceiver. My transceiver can barely receive for that ...
11
votes
2answers
975 views

What does a SSB frequency actually indicate?

An SSB signal is an AM signal with the carrier and other sideband filtered out, if I understand correctly. As such, when specifying an SSB frequency do you specify the carrier frequency, then state ...
8
votes
2answers
1k views

What is the point of a SWR/power meter where the needles cross over each other?

There are SWR/power meters with two separate gauges, and others that have them mounted so the gauge needles cross over each other. Aside from looking cool, does the cross-over point of the two meters ...
6
votes
2answers
604 views

Can I transmit on 2 frequencies simultaneously?

Lets say I want to call out CQ on 145.340, 145.940, and 146.140 at the same time, am I allowed to call simultaneously on all three then monitor all three for replies?
3
votes
3answers
254 views

Am I allowed to transmit on one repeater and receive on another?

Lets say 2 people can receive on 2 repeaters equally, but one hits a repeater transmitting better and the other person hits the other repeater better. Am I allowed to transmit on one repeater, and ...
7
votes
2answers
145 views

Which band will I be authorized the most bandwidth?

Lets say I want to do a bit of experimenting with some high bandwidth uses for transmitting data, high quality voice, etc. Which Amateur band will give me the maximum bandwidth, and what is the ...
11
votes
2answers
265 views

Why do satellites receive and transmit on different bands?

Most satellites I've found transmit on VHF and receive on UHF or vice versa. Why is this? I would think there's enough space on a single band.
6
votes
1answer
244 views

Why do some antennas list modulation type alongside power rating?

Looking at HF antennas I've noticed that occasionally I'll see power ratings similar to "200W (SSB)". Why would the modulation matter for an antenna's power output rating, and in the absence of other ...
4
votes
1answer
498 views

Do people really do GMRS liscenses [closed]

Sometimes on my Chinese uhf/vhf amateur transceiver, which goes all the way to 520 megahertz, i listen to GMRS/FRS/MURS frequencies. I always hear little kids messing around in the neighborhood on ...
6
votes
2answers
1k views

Dummy load construction and heat dissipation

I'm building my own dummy load, consisting of resistors submerged in liquid paraffin (or something similar, not 100% decided). I had some questions around heat dissipation and how I can calculate ...
8
votes
3answers
4k views

How do I extend broken coaxial cable?

I have a piece of 75 ohm coaxial cable of unknown type (outer diameter is around 7 mm) which has developed a breakage in the center conductor (which is stranded). This cable is an adapter cable which ...
13
votes
5answers
4k views

How does a folded dipole work?

A folded dipole is like an ordinary dipole, but with the ends extended and folded back, until they meet. Although it looks like a loop, I'm told it behaves similarly to a dipole. How does this thing ...
7
votes
1answer
398 views

Is it safe to mount an active scanning antenna close to an hf antenna?

I live in the centre of a seaside town in the UK. Because of lack of space I have a random wire antenna in the loft of a small house, and pick up a lot of noise on the top band Sunday morning CW ...
3
votes
3answers
121 views

Is a guest-operator QSO recorded in the host-station log too?

Just what the title reads. An amateur may operate outside his own shack from another operator's station, or from a club-station etc. As a matter of protocol, the guest operator is expected to ...
14
votes
4answers
5k views

What does the addition of a shield to a small loop accomplish?

A small shielded loop is an antenna with a loop of wire, smaller than 1/10th of a wavelength in diameter, also surrounded by a shield. Often, they are constructed from coax. There is a gap in the ...
6
votes
2answers
2k views

What are the default repeater offsets on 70cm in different countries? [closed]

I am looking for a reference list of the default repeater offsets by frequency and country on the 70cm band, to supply it into a radio control software. Most radios come with a list built-in, but the ...
3
votes
1answer
148 views

Conducting a slow scan television net via an FM repeater [closed]

I've heard the Houston AMSAT Net sends slow scan television pictures as part of its regular proceeding. Is this unique to them or are there other examples out there?
10
votes
4answers
293 views

What sources of power are useful in emergency situations?

Situations that call for emergency operating usually have some hams working in field conditions. Relying on the mains grid could be problematic. A lead-acid battery would probably be heavy to lug ...
10
votes
1answer
11k views

What is a waterfall display?

High-end transceivers apparently come equipped with a water-fall display - something to do with improved spectrum visibility. This is supposed to lead to potentially higher QSO count and rate. What ...
3
votes
2answers
1k views

Which HF transceivers feature a built-in Ethernet port for remote operation? [closed]

I would like to compile a list of HF transceivers that feature an Ethernet port (RJ45) for remote internet operation. It would also be interesting to add the supported operating system(s) for remote ...
2
votes
3answers
3k views

Choke at antenna and feedpoint?

I'm planning on putting up a G5RV. From the ladder line I connect 5m coax to the shack; would it be worth doing a common mode current choke at both the antenna feedpoint and the coax feedpoint? (I ...
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 ...
6
votes
2answers
5k views

Does a person still need a ham radio license?

Way back when, if my recollection is correct, the requirement for using ham radio was to have a license and the required skill was some level of Morse code proficiency. I have heard that Morse code ...
7
votes
2answers
204 views

Moving from Australia to the US, Amateur radio license transfer?

Moving from Australia to the US, is there a way to transfer my license in any way, or do I need to sit the exams in full? I'm wondering if there is any concept of "credit" towards licensing, so I ...
1
vote
1answer
239 views

What is this RF connector?

And what will I need to mount it in my wall? I'd like to mount it similar to the below images in my wall. Will I need any additional adapters/converters? So to put all my questions in one place: ...
9
votes
3answers
6k views

What is the electrical shock risk of an antenna?

I've seen people refer to avoiding touching an antenna or bare transmission line that might be transmitting. What voltage potentials and currents are commonly found on typical ham radio antennas? Do ...
6
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 ...
7
votes
1answer
589 views

Is bending the tips of the antenna wires going to affect the effective length?

I'm looking at designs for low cost DIY yagi antennas for a fox hunt, and pondering coat hanger wire and PVC piping. I'd like them to be built by the youth who will be doing the fox hunt, but that ...
10
votes
1answer
240 views

What is body blocking, and does it work with a stock HT on a foxhunt?

I've heard that you might not need a special directional antenna to participate in a foxhunt, that some people are able to use their body to help determine the direction of a signal. How does this ...
7
votes
1answer
409 views

Is FM appropriate for foxhunting?

I'm thinking about an inexpensive way to create a foxhunt kit for youth groups, and am wondering if the cheap dual band HTs could be used. However, it occurs to me that FM doesn't provide any good ...
8
votes
1answer
362 views

Simple cheap foxhunting?

I'm currently looking to do a foxhunt for a youth group, and need to keep it inexpensive and easy enough that it won't be impossible for those new to foxhunting and ham radio, but difficult enough ...
7
votes
2answers
236 views

Is any licensing require to receive in the amateur radio bands?

I'm considering hosting a foxhunt for a local youth group (scouts, in this case), and one of the questions asked was whether those searching for the hidden transmitter need have a license of any sort. ...
12
votes
1answer
6k views

How is the IF for a superhet selected?

There seem to be almost as many choices for the intermediate frequency (IF) as there are superheterodyne receivers and transceivers out there. The ones I have come across are 455 kHz, 452 kHz, 1.6 MHz ...
13
votes
3answers
3k views

Is a vertical noisier than a dipole, and if so, why?

I've had people tell me, anecdotally, that a vertical is noisier than a dipole. Is this true, and if so, why? If it is true: Is this additional noise, such that SNR is degraded, or is the vertical ...
4
votes
1answer
200 views

What would letter T mean in this radio beacon message?

I'm currently picking up signal from a beacon using RTL-SDR and decoding the Morse code on a computer using gMFSK program. The beacon is sending message which decodes as "T DE YU1VHF LOC KN04OO". I ...
16
votes
2answers
1k views

Is there a disadvantage to using a cheap HT for APRS?

Looking to build a cheap (not even inexpensive, just dirt cheap) APRS beacon transmitter. Right now you can get a dual band handheld transceiver with rechargeable battery, antenna, etc for under $31 [...
2
votes
1answer
2k views

Homebrew 20M SSB receiver design? [closed]

I'm looking for as simple as possible homebrew 20M SSB receiver design. I just want to start listening, but at the same time learn some radio fundamentals. So rather than buying a shortwave receiver ...
18
votes
5answers
14k views

Why do folded dipoles have greater bandwidth than ordinary resonant dipoles?

This is something I've read in passing, but never encountered an explanation of why. For example, Wikipedia says: Another common place one can see dipoles is as antennas for the FM band; these are ...
6
votes
2answers
3k views

80/160m Shortened Dipole Trap Questions

I seem to have forgotten some things I learned years ago for my amateur radio exams. If I am building a 2 band shortened dipole and want a trap between 80 and 160 do I make the trap resonant on 80 or ...
22
votes
3answers
490 views

What is the body of knowledge the U.S. written exams test?

I'm considering getting a U.S. amateur radio operator license. If you want to study to pass a license test, there are many resources to learn the answers to the entirety of the question pool: online ...
10
votes
2answers
668 views

Can an amateur use cellular technologies with SDR?

Software Defined Radio is opening up many new possibilities for amateur digital modes. One family of technologies that interests me is cellular. 2G GSM voice/sms and 2.5G GPRS data has been proven to ...
12
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?
6
votes
2answers
435 views

Is it possible for an amateur to transmit ATSC?

Amateur television has long used the NTSC (analog) television standards to transmit video and audio. Several years ago, the digital broadcast television transition made higher-quality television ...
6
votes
2answers
310 views

Is it possible to overload APRS?

Does APRS have a limited capacity in terms of beacons? What happens when an APRS frequency experiences a large number of packets?
12
votes
3answers
589 views

What is the role of digital data modes in emergency communications?

Emergency operations are typically reliant on voice traffic today. Are digital data modes used at all in emergency operations, and why/ why not? Couldn't data modes be used to pass information more ...
7
votes
2answers
98 views

Does AM demodulation make use of the redundant information in both sidebands to eliminate noise?

XLR microphone cables, for example, make use of the dual channels out of phase to cancel noise by injecting the inverted and non-inverted signal into one end of the cable. Then any noise injected ...

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