Questions tagged [rf-power]
Questions about power ratings and restrictions, including maximum power by law or for certain components, or about calculating power in certain situations.
23
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2
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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 ...
12
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2
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What are the (US) rules about unlicensed low-power transmissions?
It is common wisdom that transmissions of any sort (perhaps unidentified, encrypted, in the FM broadcast band, etc.) are permitted if they are sufficiently low power.
Where are the FCC regulations ...
18
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1
answer
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How does an SWR meter really work?
For ham radio operators, the SWR meter is a ubiquitous piece of equipment. There are dozens of standalone models on the market and most modern transceivers and antenna tuners have this functionality ...
2
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6
answers
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How to make an RF probe for accurate power measurement at QRP power levels?
Typical SWR meters don't measure forward power very accurately at the lower end of the scale, which can be a real problem at QRP power levels. Better power meters like the Bird model 43 are expensive,...
6
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3
answers
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How should this SWR meter's directional coupler work?
I'm wrapping up a "home build" of the MFJ-941EK antenna tuner kit and having trouble getting the wattmeter calibrated. I can't use C4 to get the reflected power reading calibrated down to 0 as is ...
6
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3
answers
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How do I power my radio in a vehicle mobile install?
I want to install a 30W mobile UHF radio in my car. I already have an antenna and mounting bracket - but how do I get power to this radio? It has an SAE bullet connector on the back - do I just need a ...
5
votes
3
answers
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How to find or derive the maximum safe input power to a receiver?
A number of my RF devices have a specified safe maximum input power, for example:
"The maximum RX power of HackRF One is -5 dBm. Exceeding -5 dBm can result in permanent damage!" source
"If you look ...
2
votes
2
answers
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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 ...
0
votes
1
answer
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Coaxial cable loss, dbm, db correlations
I am very confused how ham operators deal with all this, because most of the information in internet is controversial.
I have coaxial cable with loss of 34dB at 100 meters at 2400mhz.
People say that ...
10
votes
1
answer
484
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Why bother to have a high power base station when mobile units are generally low-power?
I want to find out why, say in a GSM/cellular system, a base station can be up to 50 watts however the mobile units can be only 100mw (for example).
Surely if the base station ever uses 50w to reach ...
7
votes
3
answers
15k
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Decibel subtraction in dBm and dB
If i have equations for subtraction of 27dBm-3dBm=27dBm how can this be written as 24 dB.
I convert the 27dBm and 3dBm -> 10^2.7-10^0.3.But how can we simply ...
6
votes
2
answers
887
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Power dissipation in transmission lines?
I was wondering, does the impedance of a transmission line have any effect on the power it dissipates? I'm familiar with the fact that an impedance equal to the load will provide maximum power ...
5
votes
1
answer
561
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What would be the typical received power of an "S9" signal?
Obviously, I would expect the amount of power at a receiver would vary greatly based on distance from, and the power/efficiency of, the transmitter. But I don't really have a good sense for what "...
3
votes
3
answers
896
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How does the Maximum Power Transfer Theorem relate to RF power amplifiers?
The Maximum Power Transfer Theorem says that maximum power transfer occurs when the source impedance equals the load impedance, when the power transferred to the load is 50%, the other 50% being ...
3
votes
2
answers
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What safety procedures should be followed when developing and testing a high power amp?
I'm designing a 300W power amplifier using the MRF300AN from NXP targeting a center frequency of 146 MHz.
Obviously I need to keep my fingers out of it and test into a dummy load, but generally ...
3
votes
2
answers
554
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How do you calculate peak voltage given VSWR caused by impedance mismatch in a 50-ohm system?
I would like to choose a feedline that is safe for the wattage at a given VSWR to avoid coax arcing.
How do you calculate peak voltage given a peak power in watts and maximum expected VSWR from ...
3
votes
2
answers
627
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Using approximate signal strength at a distance to estimate reception strength of a radio station
I have some historical data on radio stations, but unfortunately, the dataset only has these variables:
the power of the transmitter, in watts
the coordinates of the radio tower
Unfortunately, I ...
3
votes
1
answer
240
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Would a switched RF attenuator be (a)symmetric?
I picked up this 0-80 dB switched RF attenuator at a flea market, with no part number or other useful markings other than the knob settings. I've tested it and confirmed that it works, but there's one ...
2
votes
1
answer
371
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What is a "feed-through load" and how does it work?
While browsing some miscellaneous RF test equipment supplies I stumbled across a two-port component sold as a "feed-thru load".
Take for example the Pasternak PE6026 (datasheet), which looks ...
2
votes
2
answers
1k
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Is my low-power VHF transmitter dangerous?
I use a Raspberry Pi for transmitting FM on 107.9 Mhz.
It uses square waves and has a power of approx 0.085 Watts, but just to be safe:
If I have a 1 watt transmitter approximately 1 metre away from ...
0
votes
2
answers
344
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measures for quantifying non-linearity of a HF linear power amplifier
I am DIYing a class-AB HF Linear Power amplifier. How to quantify the non-linearity of this amplifier. What are the common measures of non-linearity as applicable to RF power amplifiers? How to ...
0
votes
2
answers
298
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Can a Loop Antenna send and receive 10,000 miles away
Can we expect a Loop Antenna such as a Chameleon F-Loop Antenna transmit and receive from the USA's midwest to Australia on HF using an average 100 watt SSB transmitter and an average receiver?
If so,...
0
votes
1
answer
448
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Calculating receive wattage given transmit power, antennae dBi and path loss
I would like to understand how to calculate receive wattage given the following (excluding feeder loss and SWR):
Transmit 50 dBm (100W) =>
24 dBi directional antenna =>
30 dB path loss =>
24 dBi ...