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
72 views

Increasing communication range by boosting output and input power

ORIGINAL QUESTION I am trying to increase the range of communication between two SDRs to simulate near space communication. The output power of TX is 10dBm but I would need 37dBm for near space ...
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1answer
38 views

Output power from the TX/RX port of the USRP N210 decreases as the frequency increases

I am trying to build an FMCW radar using a USRP N210 with a CBX40 daughterboard. I generate a sweep from 1.5GHz to 5GHz. According to their respective datasheets, the daughterboard and the USRP should ...
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5answers
108 views

Does 3 W vs 5 W TX power make a huge difference in QRP CW operation?

I've bought the QCX+ 40 m band radio. I will be powering this off a 12 V battery. I read on the manual the RF power at 12 V is just 3 W whereas on 15 V it is 5 W. Should I buy a boost converter for ...
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2answers
47 views

Where can I find a table listing the maximum PEP per band?

I'm building myself an Excel Cheat Sheet.
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1answer
43 views

What is the maximum antenna cable length allowed in GNSS application?

I am beginner in designing GNSS receiver design and facing concern while testing the high precision GNSS survey.I am using GNSS survey grade antenna for my GNSS receiver application testing, the ...
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2answers
313 views

Importance of Ferrite Size in Coax Choke Balun

The question is quite simple: When making a coax choke balun, does the size of the ferrite matter, and if so, why? I have seen design notes that say to use a single FT240-43 toroid for powers up to ...
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2answers
87 views

Power vs. Bandwidth

A 10 watt transmitter is transmitting a 700 hz tone in a 3 kHz wide band. If the power is increased to 1000 watts will that not increase the bandwidth if the data (700Hz tone) remains constant? What ...
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5answers
257 views

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,...
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1answer
139 views

Signal power measurement

I have a radio with a nominal output of 1-30mW (frequency dependent) and amplify this with a 21.8dB capable amplifier (frequency dependent, but should be ~150mW). The signal output then passes through ...
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2answers
86 views

Estimating near-field electric field strength at LF (137 kHz)

I'm experimenting with low frequencies, but due to the inherent nature of LF, I strive for more transmit power and bigger antennas. Now of course I want to comply with regulations, which allow (in my ...
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1answer
56 views

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 ...
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3answers
100 views

How safe is 100 watts on 2-40 meters?

So I have the misfortune of being an apartment dweller. I know that 50 watts is pretty safe as it is what first responders use on 2 meters. Am I really going to have to run around with an analyzer ...
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87 views

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 ...
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2answers
178 views

What kind of filter should be used at the output of HF linear amplifier?

I am looking for a output filter to use with a HF linear amplifier called miniPA70 which is available through several online auction sites. The circuit is available here : http://iu3idf.blogspot.com/...
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3answers
275 views

Can a carrier operated relay be used for T/R switching in a HF linear amplifier?

I am building the T/R switching circuit for an HF linear amplifier covering 80m band to 20m band. The current circuit takes a potential-free contact from the exciter and use this contact to turn on/...
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1answer
282 views

SO-239 (UHF) vs N connector power handling on 160m

I am curious how much CW power an N connector or SO-239 connector will handle on such a low frequency like 160m band. I know on VHF they will probably handle about 800W before getting too warm. I ...
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1answer
185 views

Legal aspects of the HackRF one / SDR in Switzerland?

I would like to know, what I can legally do with SDR / a Hack RF One in Switzerland? What are the limitations concerning sending and receiving? Do I need any licenses for that? If so, which ones, ...
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3answers
562 views

Cheap antenna for new HF HAM

I just got a 100W HF radio and I am new at this. What is the cheapest antenna I can hook up without burning up my radio or shocking myself?
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1answer
93 views

Wifi inside a rocket

I want to understand, as most rocket uses LAN cable and switches to communicate between stages. Is it possible to replace with WiFi? Although it's will be complex system but one idea to make each ...
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1answer
143 views

Passive antenna system as a Wi-Fi repeater [duplicate]

I want to extend WiFi signal using a passive repeater between two isolated boxes (have to make both box wireless). Transmitter antenna from box A is placed in the gap between box A and B. In the same ...
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3answers
272 views

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 ...
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2answers
91 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 ...
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1answer
414 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
68 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. ...
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2answers
175 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 ...
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2answers
591 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 ...
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2answers
132 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 ...
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2answers
219 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 ...
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1answer
74 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 ...
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1answer
243 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 ...
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1answer
197 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 ...
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1answer
77 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
312 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
77 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
128 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
67 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 ...
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2answers
794 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
104 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
79 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 ...
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2answers
1k 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 ...
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2answers
385 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 ...
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1answer
113 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
194 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 ...
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1answer
140 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
196 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
1k 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 ...
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1answer
805 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
266 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, ...
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2answers
6k 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 ...
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1answer
3k 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 ...