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1500 questions
10
votes
2 answers
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 this roughly work?
Cobe
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10
votes
3 answers
Why are germanium diodes specified in amateur radio designs?
It's somewhat common to find a schematic that calls for a germanium diode in amateur radio contexts. For example:
This is a QSK circuit from the Fldigi manual.
And yet, purchasing a germanium diode is a relatively difficult task. For example,…
Phil Frost - W8II
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10
votes
4 answers
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 around should the operator need to relocate in a…
VU2NHW
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10
votes
2 answers
Buddipole model comparison
Can anyone give me some insight into the different Buddipole models available? They look pretty similar to me except for the sizes. What would make you choose one over the other?
s3c
- 837
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10
votes
3 answers
Using MIMO in Amateur Radio?
MIMO, Multiple Input, Multiple Output, is used widely in commercial data transmission. 802.11n and LTE devices use it to increase throughput, link reliability, and channel usage without increasing transmission power or using more bandwidth.
While…
Adam Davis
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10
votes
2 answers
APRS digi path for ISS digipeater?
So when I try to work the ISS digipeater, what should I set the digi path to be?
My setup is a 5 W HT with a 2 m yagi connected to my phone with APRSDroid.
I've tried the past few nights with ARISS R0ISS and WIDE2-2 and none seem to get picked up…
JW03
- 103
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- 4
10
votes
3 answers
Stealth HF station setup advice
I need some advice on setting up my first HF station in a somewhat restricted townhouse community. If I had a detached house with a backyard I’d probably already have everything setup. But with this townhouse I keep second guessing what to…
ifletch
- 133
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10
votes
3 answers
Does modulation affect propagation?
Does the modulation scheme, whether OOK, SSB, AM, FM, a digital mode, etc, affect the propagation of a signal?
Adam Davis
- 12,125
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10
votes
2 answers
What is the actual loss in a feed line with high SWR?
It is well-known that it is unwise to have standing waves on the feed line between one's antenna and one's transmitter, unless it is a very low-loss type (e.g. ladder line), because the transmitted signal is reflected multiple times through the feed…
Kevin Reid AG6YO
- 24,506
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10
votes
2 answers
What determines power handling capacity of an antenna?
I just bought a cheap 1/4-wavelength, 2m. mag-mount antenna. The package says it can handle 50 watts. I can think of three things that could limit the capacity:
$I^2R$ losses in the connection to the feedpoint and in the antenna wire itself:…
Pete NU9W
- 950
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10
votes
2 answers
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 point to earth.
Receiver is on Earth. Antenna is…
BarsMonster - R2AYN
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10
votes
2 answers
Where on the web can I find a calendar of upcoming contests?
For years, I have been using SM3CER Contest Service for HF contests.
It is always good to have a backup, so I am looking for more or better.
What do you recommend?
on4aa
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10
votes
1 answer
What is emissions designator "E" when used as a type of modulation?
The FCC's rules regulating amateur radio, in 47 CFR 97.307(f), paragraph 8 defines one emissions standard/limitation as follows:
A RTTY or data emission having designators with A, B, C, D, E, F, G, H, J or R as the first symbol; 1, 2, 7, 9 or X as…
natevw - AF7TB
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10
votes
4 answers
How to operate on HF if an AM transmitter is only 540 feet away?
I'm a General Class Licensee, and due to pulmonary disease I cannot operate voice. I am also about 540 feet from a 24/7 1 kW AM station. The signal is so pronounced that most audio devices in the house pick up the station. Every shortwave receiver…
Gordon C
- 101
- 2
10
votes
1 answer
Why do we use decibels in radio?
We can measure power in watts, and gain or loss in unitless ratios. So why bother using decibels for these things?
Phil Frost - W8II
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