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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What is the difference between antenna input impedance and its radiation resistance?

I got to know that the input impedance of the halfwave dipole antenna is given as: Zin=1/Im* sin(β(H-|Z|)) where Im is the maximum current on the antenna( when excited with a 1 volt supply), H is the ...
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  • 43
0 votes
1 answer
69 views

What power levels do the Baofeng UV-5R/5RA/5RE have? [closed]

What are the power settings of handheld radios of the Baofeng UV-5R series in watts?
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1 vote
1 answer
58 views

Does a filter or inductor's power rating matter in its passband, or only in the attenuated frequency range?

I would like to build a high-pass filter that would block reception of signals from the United States' FM broadcast range (88–108 MHz) while still allowing me to transmit VHF ham signals (around 146 ...
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1 vote
3 answers
126 views

What can be used to protect an SDR receiver against bursts?

I am using a USRP B205 to detect electromagnetic pulses. Sometimes the signal power bursts to 100 dB, average power is around 10 dB. What can be used to protect the SDR receiver against bursts?
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  • 622
6 votes
2 answers
107 views

Power rating of a selfmade air coil

A colleague was winding an air coil himself. It's a 110µH coil with 200 windings for an 80m antenna, intended to be used on a 600 W transceiver. He used a copper lacquer wire with 0.6mm diameter. ...
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3 votes
2 answers
144 views

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 ...
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  • 307
2 votes
2 answers
119 views

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 ...
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  • 307
2 votes
1 answer
85 views

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 ...
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0 votes
2 answers
108 views

Why is there so little difference in the gains of Yagi Uda antennas with omnidirectional antennas? Shouldn't the power at the back be at the front?

Consider an omnidirectional antenna with X dBi gain. Intuitively I understand that the power that would have been dispersed in now-dead directions is directed around the antenna. What I don't get is ...
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0 votes
0 answers
47 views

How do you take into account the SNR of a transmitter in a fade margin?

I have a fade margin for a RF bridge, but it only compares the sensitivity of the receiver to the received power - or alternatively calculates the Eb/N0 from the net received power divided by the ...
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-1 votes
1 answer
72 views

Acoustic Communication issues [closed]

[![I've attached schematic, I am connecting transducer directly to that header pins on receiver side. On transmitter side I am connecting op-Amp to boost voltage to +10v -10v.][1]][1]I am working on ...
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1 vote
2 answers
74 views

Is power output or something else to blame for my duplexer failing?

A Ham buddy of mine and I were trying to setup a UHF repeater in our area due to a lack of them. We had two Motorola CDMs, one a 1250 and one a 1550, and we purchased a $200 or so reject only duplexer ...
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5 votes
1 answer
75 views

Acceptable RF radiation exposure to electronic equipment

I'm wondering if there are any general guidelines or rules of thumb about the exposure of electronic equipment to RF transmissions, 150 MHz - 900 MHz. The background is that we are looking to install ...
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3 votes
1 answer
221 views

Troubleshoot ICOM IC-745 intermittently shows no power on transmit

I have an old IC-745 I bought used last year. Recently it seems to be malfunctioning intermittently. It is receiving well on all bands as far as I can tell. Sometimes when transmitting, there is no RF ...
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  • 160
4 votes
2 answers
266 views

Is the 1.5kW power limit per antenna? What about antenna arrays?

My son KJ7NLL just got his general, and while we don't (yet?) have plans to transmit at 1.5kW, he asks if the 1.5kW limit is per-antenna? If it is per-antenna, and you use an antenna array of 8 ...
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  • 307
0 votes
2 answers
91 views

Repeater design using round robin transmitters to increase duty cycle?

I would like to build an FM repeater using a short stack of Kenwood TK-890H rigs adjusted to 70cm USA amateur band, but the model has a 100W rating with a duty cycle of only 20%. 20% isn't nearly ...
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1 vote
2 answers
141 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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  • 11
2 votes
2 answers
173 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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  • 21
2 votes
5 answers
207 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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  • 247
0 votes
2 answers
218 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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1 vote
1 answer
147 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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9 votes
2 answers
1k 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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  • 223
1 vote
2 answers
460 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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2 votes
6 answers
2k 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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  • 8,922
1 vote
1 answer
184 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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  • 125
2 votes
2 answers
128 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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  • 23
0 votes
1 answer
199 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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  • 307
2 votes
3 answers
811 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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0 votes
2 answers
182 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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  • 113
1 vote
2 answers
839 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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  • 113
0 votes
3 answers
816 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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  • 113
1 vote
1 answer
795 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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  • 425
2 votes
1 answer
418 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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  • 21
5 votes
3 answers
1k 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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  • 151
-4 votes
1 answer
123 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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0 votes
1 answer
264 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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1 vote
3 answers
646 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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  • 3,409
1 vote
2 answers
126 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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  • 113
7 votes
1 answer
837 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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  • 7,683
1 vote
0 answers
94 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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  • 7,683
3 votes
2 answers
287 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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3 votes
3 answers
2k 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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7 votes
2 answers
596 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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5 votes
2 answers
227 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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  • 740
2 votes
1 answer
198 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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3 votes
1 answer
495 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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6 votes
1 answer
243 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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  • 740
3 votes
1 answer
85 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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5 votes
2 answers
519 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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  • 2,715
2 votes
1 answer
151 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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