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1500 questions
7
votes
2 answers
What are the regulation requirements for running a repeater?
When I try to find information on the requirements to run a repeater, I just see a lot of results related to building one. But I'm wondering about USA regulations.
Does one need a particular license?
Which frequencies are allowed?
Can/should…
Bort
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7
votes
2 answers
FT8 callsign/maidenhead compression encoding
I have set myself a challenge to write a Matlab script as proof of concept to send an FT8 CQ call (not necessarily for live transmissions yet, but I may extend the project). So far I have:
Generated and appended 14-bit CRC to precomputed message…
jemussi
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7
votes
3 answers
APT/LRPT images geotagging
I want to extend functionality of some open-source programs which decode APT and LRPT images (wxapt and glrpt). More specifically I want to add possibility to overlay geographical data such as land borders, administrative borders, rivers etc on the…
Drobot Viktor
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7
votes
2 answers
Looking for a schematic of a DIY circulator
I would like to build a simple HF, VHF or UHF circulator to get a better understanding of how these devices work. Sadly at the moment I'm unaware of any articles or books that provide corresponding schematics and description. Could you please…
Aleksander Alekseev - R2AUK
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7
votes
3 answers
Why EME with 100W and a single Yagi-Uda antenna is possible?
Recently I've been reading about EME and there was one thing that surprised me. Many sources claim that EME has path loss for 2m band about 252 dB. In the same time they claim (one, two):
Recent advances in digital signal processing have allowed…
Aleksander Alekseev - R2AUK
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7
votes
2 answers
CW: when I supposed to send "E E"?
I'm new to CW and one thing I couldn't figure out is when I supposed to send "E E". Let's say I'm calling CQ and somebody answers me. The QSO is almost over. Should it be ended like this:
- TNX FER NICE QSO 73 E E
- GDX 73 E E
... or:
-…
Aleksander Alekseev - R2AUK
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7
votes
1 answer
What exactly was a decremeter and how did they work?
In A Century of WWV, I found this mention of an unusual sounding instrument that may have once been commonplace:
Calibration work was mainly focused on decremeters, instruments designed for measuring the decay, or decrement, of a pulsed radio…
natevw - AF7TB
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7
votes
2 answers
Why aren't "ghosts" and intersymbol interference due to unmatched impedance (high SWR) a concern for HF receivers?
In amateur radio, we care about impedance matching when we need to keep the load within the equipment's specification (for best performance, or just to avoid damaging a transmitter), when we want to maximize the power delivered into the load, or…
比尔盖子
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7
votes
1 answer
Coherent CW synchronization?
When using coherent CW, how is the receiver frequency and/or Morse Code dot clock synchronized to the transmission precisely enough to allow for synchronous decoding?
hotpaw2
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7
votes
1 answer
What does the Friis transmission equation represent and how is it derived?
I've read that the Friis transmission equation can be applied to calculate path loss in ideal space. However, I'd like to better understand the factors that define it and what it represents, and why it is the equation it is.
Phil Frost - W8II
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7
votes
1 answer
Regenerative receiver interference?
Can a regenerative shortwave receiver (especially an old vintage unshielded tube or transistor model) connected to a wire antenna generate HF interference? If so, what are some ways to prevent one from generating such interference (but still…
hotpaw2
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7
votes
1 answer
How to measuring ferrite core efficiency vs frequency
There is an unknown ferrite toroid. I would like to figure out whether it can be used in an audio transformer, or maybe in a 1:4 transformer on given HF frequency.
The experiment I came up with is following. I can wind a 1:1 transformer using this…
Aleksander Alekseev - R2AUK
- 4,307
- 18
- 55
7
votes
1 answer
How does a Faraday cage block an EMP?
If you search the Internet for Faraday cages, you'll find a lot of information about using homemade cages to protect radios from EMP damage while in storage. A lot of that information is either contradictory or isn't backed up by satisfactory…
mrog
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7
votes
3 answers
Using 75 Ω instead of 50 Ω coax feed
Can I replace my old 50 Ω coax with RG6? It's cheaper and less loss at VHF/UHF. I would match by L/2 multiples of coax to repeat input and output impedance or L/C matching networks at each end.
Is this a viable alternative to expensive 50 Ω coax and…
R Johnson
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7
votes
3 answers
Is there a public standard for 8 and 10 character grid locators?
We have a question about the algorithm for conversion from coordinates into grid squares here, and this is an extension of that.
I've noticed that there are several web-sites (for example here, or here, or here) and Android applications which will…
AndrejaKo
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