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.

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2answers
64 views

Matching a 188 ohm antenna to an unbalanced input that expects a 50 ohm antenna

I am new to RF field and trying to use an Archimedean Spiral Antenna design from this paper to capture 915MHz RF for the P2110B power harvester chip. The estimated antenna impedance is 188 Ohm (see ...
7
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1answer
69 views

Double power-handling ability of RF amplifier output transformer

I want to base the output network for a 500W push-pull HF amplifier on "A 250W Broadband Linear Amplifier" described in Chapter 17 of the 2014 ARRL Handbook. I need advice on whether and/or how the 1:...
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0answers
59 views

Parasitic inductance of relay contacts

I need to switch a bank of filters operating on bands from about 2MHz to 30MHz. The parasitic series inductance of the relay contact system will have an effect on the performance of my system. ...
3
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2answers
70 views

Determining whether signal meets the 12 dB SINAD voltage

The specification for a certain radio receiver says: Typically 12dB SINAD NBFM for 0.15uV at 145MHz. If I understand correctly, this means that the received radio wave should have a voltage level of ...
2
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0answers
90 views

Yaesu FT-891: power drops to 50% when TNR is ON and SWR is 1.5:1

I noticed a weird behavior of my Yaesu FT-891 transceiver. I'm using it with an external autotuner mAT-30 (120W SSB/CW, 30W PSK31), which is compatible with Yaesu FC-50. When I connect a 100W 50 Ohm ...
5
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2answers
72 views

distance between shack and antenna

I am putting a 40m antenna in my attic and I was wondering would it be safe to have a shack in the room right below the attic (10ft of coax or less) or should I have my shack in the basement/ground ...
3
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2answers
165 views

Can I have a signal generator on while it's not connected?

The unit in question is an Elecraft XG3 test signal generator. It puts out anywhere from -107 dBm to 0 dBm. Is it safe to have these signal generators on and transmitting while not connected to ...
2
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1answer
41 views

Attenuator Cascaded Connection

PAT1220-C-10DB-T5 is a 10dB attenuator. (This chip is just an example, it could be any other component as well). Can I simply connect 3 of them in series in a PCB design to make my cheap 30dB ...
3
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1answer
63 views

Selecting Directional Coupler for VSWR Measurement

Assume directional coupler is coupling with 16dB attenuation when signal is traveling from input to output. And directivity is let's say 20dB. If I understand correctly, when the RF signal is ...
4
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1answer
171 views

Is it safe to run two barefoot rigs on one antenna with an AB switch?

I have a Daiwa CS-201A two position switch. The single side is connected to by quarter wave vertical (40m). The A and B sides are connected to an IC-7300 and TS-830S. The switch is claimed to have ...
3
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1answer
68 views

Is there a technical reason to sell an LNA without advertising its gain?

I recently bought a couple SPF5189 low-noise amplifier boards via an online marketplace. One thing that struck me is that while nearly all the listings highlighted the LNA as having a noise figure of ...
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2answers
99 views

What additional information do I get from an RF ammeter, as compared to a regular SWR/wattmeter?

I've grown up using SWR/power meters. They're "simple" devices: They show forward and reverse power, and show the standing wave ratio. They, however, do not show antenna efficiency. New hams are ...
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1answer
56 views

Can an indoor antenna damage unshielded electronics?

I have a 25w radio running through a ~4.5db gain antenna. If I use a 4W HT indoors, I can hear a loud buzzing noise emmanating from my computer speakers. If I used the 25w mobile with the 4.5db gain ...
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1answer
47 views

Measuring S21 against TX-RX distance (a.k.a path loss modelling) with a network analyzer didn't give expected results

Task: Path loss modelling Target frequency: 433 MHz; Laboratory environment: in a basement where there were other equipment and metal shelves. A few acoustic absorbers were placed around the setup. ...
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2answers
59 views

What would the power at output at a distance of 1cm when transmitted at a power of 1dBm from the transmitting antenna?

If the transmitter and receiver are placed one centimeter apart, what would be the power at the receiving end if the tranmission power is 1dBm? Consider an omnidirectional antenna. And if it is a ...
4
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2answers
285 views

dBm signal minus dB

I've got a 27dBm signal that I'm going to put through a 6dB attenuator. How do I work out the resultant signal in dBm? I've tried Googling that without any luck.
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1answer
57 views

How to measure the power emitted from an HF antenna in near-field WPT?

I'd like to estimate the power density from a 13.56 MHz power source in a near-field WPT (wireless power transfer) scenario. Using a spectrum analyzer with a receiving antenna will give the E-field ...
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1answer
74 views

Why does signal power drop every night?

I have been monitoring power of a P25 control channel (at about 850MHz). For awhile, 24 hours a day. I graphed the power over a couple of weeks and it is almost sinusoidal, decreasing significantly ...
5
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2answers
202 views

What is inside a 50 ohm termination?

I see RF applications requiring 50 ohm termination to avoid any open port reflections. Curious what is actually inside a 50 ohm termination connector. Is it simply a 50 ohm resistor? But then it is ...
2
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2answers
235 views

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 don'...
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1answer
99 views

How is RF Power at Receive Antenna Output Terminals Calculated?

Is the Friis equation sufficient to make this calculation? Must other considerations also be evaluated?
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1answer
109 views

SNR measurement for a BPSK/QPSK signal

I have created a software (gnuradio) that performs modulation/demodulation and supports a number of modulation schemes and error correcting codes. I'm in the process of evaluating the BER vs SNR for ...
3
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1answer
113 views

Restoring full output power to rig with tube finals

I have a TS-830S that was initially doing about 60W in CW at 10m and 70W at 40m. I've heard these things are capable of at least 100W. Determined, I started doing research on what components to look ...
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2answers
121 views

Peak envelope power should be 2:1 or 4:1 on meter?

I've always been reading my AM modulated signal on a Bird wattmeter and trying to set the carrier to 1/4 of the peak envelope power (PEP). Recently, I was told by a CBer that you only can see it that ...
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2answers
477 views

USRP Safe Gain Values

I am working with USRP N210 and USRP B200 radios with GNURadio. I have connected the TX/RX port of one radio to the RX2 port of the other with an RF cable as a simulated radio link. In GNURadio, I ...
3
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1answer
397 views

Why does the output power of some AM transmitters increase when modulated and of others decrease?

I didn't fully understand all the finer details of AM, so I'd like an explanation for the following behavior: I have 3 radios. In AM mode, one of the radios, when modulated, increases output power ...
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1answer
151 views

Intermittent High SWR

Using a Cushcraft MA5B beam, when I apply high power from an amplifier, the SWR will go up and down intermittently. Something is breaking down at high power (200-500 W). I have a new coax feedline, ...
5
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2answers
3k views

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 ...
16
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1answer
2k views

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 ...
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2answers
146 views

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,...
2
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2answers
448 views

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 ...
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2answers
372 views

calculating power from directional coupler

I've designed an pulsed RF generator (50-100 MHz) and am using a directional coupler to measure power into a 50 ohm dummy load. The forward power from the coupler is plugged into a o-scope (hi Z ...
2
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1answer
73 views

TX output power increase when fed through filter

I came across a weird case, I have a low power 440MHz repeater transmitter, which I thought to set at about 10 watts. I made this measurement using an accurate offset attenuator and service monitor. ...
2
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2answers
522 views

What is output power exactly?

I'm trying to comprehend what one would see if one could observe what's happening in the antenna wire. Is the difference between a 1 watt and a 4 watt transmitter just that the amplitude/voltage on ...
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1answer
87 views

RF connector between mobile phone and transmitter = complete shielding?

When connecting mobile to transmitter with RF cable: Does RF connector provide complete shielding for the transmitter signal ? Does it prevent the mobile from receiving other signals from other ...
4
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2answers
753 views

What is the purpose of limiting radio output power?

According to article 25, section I, § 4 (25.7) ITU's Radio Regulations: The maximum power of amateur stations shall be fixed by the administrations concerned. In my country this is 500W for CEPT ...
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2answers
1k views

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 ...
3
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3answers
297 views

Why is coax loss logarithmic?

With DC hookup wire, losses are directly proportional to length. If the resistance of 100m of wire is 10 ohms then the resistance of 200m of wire will be 20 ohms. But we measure coax loss in decibels ...
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3answers
900 views

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 ...
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2answers
118 views

Laptop screen goes blank when transmitting from handheld within a few feet - sometimes

I noticed that when I transmit from my handheld Baofeng Radio, with the standard rubber duck antenna, that my laptop screen goes blank. This only occurs if I'm within a few feet, and even on powers ...
2
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2answers
161 views

RF scanner w/ graphic output

I debated putting this question on the electrical engineering forum vs. here. I settled on here since I figured many of you amateur radio experts have probably wondered about this too. I am ...
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1answer
132 views

Signal booster with transistor

How can I make a simple signal booster without introducing too much noise? My first thought was to just feed the signal into transistor base (capable of 4GHz) through a 1K resistor. I could get a 1.2W ...
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2answers
66 views

Extracting received power info from teletype like audio

Is it possible to digitally extract received power info (like VU meter perhaps) from and PSK31 audio (or alike), actually the mode for text encoding over audio hasn't been chosen yet and the ...
4
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1answer
357 views

Why does path loss decrease as frequency decreases? [duplicate]

The Friis transmission equation can be given as: Pr = Pt + Gt + Gr + 20 log10 (λ / 4πR) Where the variables represent: ...
5
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1answer
247 views

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 "...
4
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1answer
75 views

Signal generator giving DC output?

My signal generator is giving DC at its RF OUT port. At 500 MHz & 1GHz it's giving nearly 1.5V DC when I measure the voltage between the centre pin & outer conductor with a multimeter. I don'...
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4answers
592 views

Is it safe to live close to cellular antenna?

I saw some apartment in my county in a very good location (quite close to the beach), however, the rent is very cheap. The apartment is the highest on that building, on top of this building there is a ...
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4answers
632 views

Max legal power with nearly zero BW

I'm developing a type of ground penetrating radar that does not use pulses. It's extremely narrow bandwidth. As narrow as a good crystal can get it. The frequency I'm shooting for initially is ...
2
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1answer
556 views

Measuring energy density of 2.4 GHz and 5.0 GHz signals

I'm a math and computer science student, starting to mess around with using amplifiers and antennas to build long-range wifi hardware in my spare time. Calculating the expected power density of a ...
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3answers
3k views

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 ...