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111 questions with no upvoted or accepted answers
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votes
0answers
144 views

UHF FM power amplifier design without expensive software

I'm designing a small UHF data transceiver for the 70cm band, based on a Silicon Labs EZRadioPro Si4463 IC. Modulation is FM, 12.5kHz channel step. The concept is similar to SiLabs' AN656 application ...
6
votes
0answers
154 views

Beyond Maximum Stable Gain of a transistor

I was plotting constant-gain circles on the Smith chart the other day for a potentially unstable RF transistor. I recently read on-line that for a potentially unstable transistor the maximum gain ...
6
votes
1answer
166 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 ...
6
votes
1answer
616 views

Doppler Shift Compensation in Inter Satellite Communication

I am currently doing a project in the area of optical inter-satellite communication (GEO-LEO). I am using a optical carrier of 281 THz, and the Doppler shift corresponding to it is ±7 GHz. I ...
5
votes
1answer
118 views

For a resonant 1/2 wave dipole, does the reflections being in phase with the applied signal cause the zero reactance seen in the feedpoint impedance?

For a resonant 1/2 wave dipole when used for transmitting, does the fact that the reflected waves on the antenna are in phase with the applied signal result in zero reactance at the feed point, or ...
4
votes
0answers
30 views

Where to find HF channel models or statistics?

When designing a waveform for packet radio usage, it'd be helpful to know a few things, mainly distribution of coherency bandwidths distribution of coherency times Whilst such statistics are ...
4
votes
0answers
73 views

Dipole loading coil winding directions?

A single inductive loading coil in a vertical or a pair of loading coils in a dipole are commonly used to match a given total antenna length parameter to a given frequency wavelength (where the ratio ...
4
votes
0answers
66 views

Is it practical to use a magnetic amplifier as an AM modulator in a transmitter?

If I'm building a vacuum tube HF transmitter (say, 40 m band), obviously the simplest mode to build is CW; it's common to key the oscillator input to the final (in order to keep the oscillator running ...
4
votes
0answers
226 views

ISS APRS Digipeater with Kam XL and ICOM IC-910H

I am trying to use the ISS APRS digipeater which transmits at 437.55MHz. Hardware setup consists of the following ICOM IC-910H. The transceiver has been connected to a Windows PC running a HAM ...
3
votes
0answers
51 views

What causes differences in properties of ferrite cores from same material?

Why are the shapes of the impedance curves different for cores made of the same ferrite material? The impedance (Z) of an inductor wound on a ferrimagnetic core is: $$Z=j\omega L_s + R_s = j\omega ...
3
votes
0answers
49 views

Can the external VFO input in a Heathkit SB-(100, 101, 102) be used to operate on frequencies outside the radio's normal range?

I've got a Heathkit SB-102 that I'm working on making operational (problems with transmit, receiver works just fine). This model radio has a 9-pin Molex connector in the back, intended to connect an ...
3
votes
0answers
51 views

What dot means in JTDX FT8 received messages?

What dot near country means in JTDX? Maybe LOTW?
3
votes
0answers
37 views

What value goes in the AX.25 PID field if the Layer 3 protocol is not defined in the standard?

I am working on space-ground networking for a Cube Satellite, and one of our candidate Layer 2 protocols is AX.25. We haven't settled on a physical layer, but it's likely to be some form of quadrature-...
3
votes
0answers
75 views

I/Q demodulation of DSBSC-AM signals

I was looking at some Stereo FM demodulators on the Internet, and I can't understand the use of the complex to real block for demodulation of the L-R signal (DSBSC-AM) which can be seen in different ...
3
votes
0answers
43 views

How to simulate two antennas in 4nec2

I need to simulate 2 helix antennae placed side by side, and see the resultant radiation pattern. But after adding the second antenna with a separate and when I try to simulate 4nec2, only simulated ...
3
votes
1answer
68 views

Somewhat-directional (cardioid?) antenna for receiving ADS-B?

I recently set up my own RTL-SDR-based ADS-B receiver. I live in a Manhattan high-rise with an eastern view, so I do not get any signals from behind the building (almost: I get the occasional ...
3
votes
0answers
78 views

Where did the LP to BP transformation $ \frac{\omega ^{2}-\omega_0^{2}}{\omega\cdot BW} $ come from?

I'm not sure this question is appropriate for this site, but I feel that if anyone knows about a filter, a radio ham knows! And as a ham myself I feel I need to understand this important area better. ...
3
votes
0answers
93 views

GnuRadio RF transmission, legal and safety issues

I'm trying to run some transmit/receive RF examples that I found online using GNU Radio with USRP B200. I read and heard about some cautions in terms of transmitted frequencies here in the USA which ...
3
votes
0answers
193 views

Kenwood TS-50 and USB to Serial

I paired my old Kenwood TS-50 with serial, by using FTDI TTL-232-5V-AJ USB to serial converter. I used ideas from here: http://steeman.be:8080/posts/TS-50%20USB%20Interface/ and here http://i.imgur....
3
votes
0answers
819 views

OFDM spectrum, HACKRF, and GNUradio companion

I am trying to analyze the spectrum of wifi spectrum. I getting a good OFDM spectrum with my HackRF at 2.412 GHz (from my first QTGUI Sink). But I get nothing out of OFDM Receiver. I was wondering ...
3
votes
0answers
1k views

TS-590 Antenna Tuner Protocol

I'm looking for the protocol used by Kenwood's TS-590S antenna tuner port. I've worked as far as I can with Kenwood's tech support. They know what the pins are labeled, but don't have any information ...
3
votes
0answers
70 views

CML FX919B Forward Error Correcting

I would like to decode de-interleaved demodulated 4FSK symbols that were transmitted using the CML FX919B chip. The datasheet only gives the following information: Forward Error Correction In ...
2
votes
0answers
32 views

Wide band TX capable band-pass filter for VHF and Airband

I want to share the same antenna for VHF (TX/RX 144-148 MHz) and for Airband RX-only (116-136 MHz). I live on a very congested area where filter is a must, so I'm looking for the best solution for my ...
2
votes
2answers
45 views

Amateur Radio License classes in Central Iowa

I'm looking for an amateur radio license class in central Iowa, near Des Moines. I've been unable to locate anything through web searches.
2
votes
0answers
69 views

Which digital modes are formally specified sufficiently to be implemented?

Which currently popular digital/SDR modes do not require a pre-compiled library or pre-written source code? (e.g. has actually been used for QSOs as implemented from specification or sufficiently ...
2
votes
0answers
33 views

Clocking A and N in a Dual-modulus PLL Prescaler

In an effort to "up my game" attempting to build a VFO for my DIY transceiver, I've been looking at PLL theory and circuits. Many of my research references are quite old and I understand that many of ...
2
votes
0answers
43 views

Icom 7300 low frequency broad-spectrum noise

What's causing these horizontal bands of noise? It's the middle of the day here in a low density city neighborhood. They were not present about 20 minutes ago; now they are even stronger and filling ...
2
votes
0answers
76 views

Unknown kit from DK0TV

When my father - who became a ham years after I did - passed away, I found an unstarted project (board + components), which I only re-discovered again years later. The board is marked DK0TV-001, and ...
2
votes
1answer
43 views

Kenwood TH-D72A and AO-91/92

I got a Kenwood HT and using it with the Elk Antenna On the radio, there is Tone and I set it to 67 Hz. I wasn’t able to break thru to the satellite and had it in Full Duplex mode. I can hear ...
2
votes
0answers
54 views

Ferrite Rod Antenna Array?

The ferrite Rod is a reasonably effective Receiving Antenna for LW MW and Lower HF spectrum .It is well known that a ferrite rod is much more effective than an air cored coil of the same dimensions ....
2
votes
1answer
58 views

voltage rating for RF filter components

I want to design a PCB for a diplexer for Satellite operations. I want to use SMD capacitors and possible inductors to get some experience with soldering SMD components. What should the voltage rating ...
2
votes
3answers
310 views

Can I build a Yagi antenna for my Baofeng UV-5R?

I would like to build a Yagi antenna for my Baofeng UV-5R, but I'm a total newbie when it comes to amateur radios. The antenna will be for UHF and shouldn't be too long (like 1.5 meters max). So my ...
2
votes
0answers
44 views

Demodulating ISO14443 (part of NFC) using SDR?

I'm looking for info on demodulating both sides of an ISO14443 communication using a cheap SDR, preferably an RTL-SDR (R820T2+RTL2832U). The application is passively monitoring an NFC exchange for ...
2
votes
0answers
60 views

First linear power supply build - design questions

I have decided to build my own linear regulated power supply to provide the power for an upcoming build. Since I'm no pro, I was hoping I could get some feedback on my design before building it, just ...
2
votes
0answers
80 views

Has this regeneration control been done?

I'm planning to build a two-tube reflexed RF regen receiver soon. I'm examining methods of controlling the regeneration — it needs to be possible to both initiate and halt oscillation in all bands (I ...
2
votes
0answers
65 views

HackRF One and IoT overloaded?

I'm transmitting Z-Wave frames using HackRF One in loop, one frame every second. Has anyone clue why are some frames not transmitted? You can see several too long gaps between frames on Waterfall (...
2
votes
1answer
96 views

How do I interpret the FCC ground conductivity files

The FCC has .seq files that show ground conductivity which it makes available for download. Unfortunately, there doesn't appear to be any documentation that comes with the files, or even headers. I ...
2
votes
0answers
208 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 ...
2
votes
1answer
360 views

GnuRadio alternative for Selector Block

Hi I want to switch between tx and rx in a flow graph with my HackRF. I found this video that shows how it could be done. The key component is the Selector block which is now deprecated. Is there a ...
2
votes
0answers
65 views

Is PC to Digital Radio possible, is there an existing solution?

Is it possible to setup up an interface from a PC to a digital radio that is able to communicate with a Hytera PD702 handheld (450-520MHz) or like type radio? Or are there off the shelf radios that ...
2
votes
0answers
31 views

Noise Floor when receiving Es'hail 2

I'm currently trying to receive the Es'hail 2 satellite using a standard TV LNB, 60cm dish and RTL-SDR. My dish is slightly offset by 2 degrees, and my SNR is only about 15dB unfortunately. My main ...
2
votes
0answers
246 views

How to decode 2FSK signal with SDR?

I'm new to radio and SDR but, as a hobby project, I'm trying to decode a 2FSK radio signal received by an RTL-SDR that I sent using an SI4463 transmitter. The record file contains 3 packets, but I'm ...
2
votes
0answers
445 views

LimeSDR Mini + Raspberry Pi 3 B+ Transmission problem

I am new at this. I would like to transmit an audio signal cleanly using WBFM but I see two signal peaks occur around my fundamental frequency when I start transmitting. In this case I am using a ...
2
votes
0answers
342 views

Does anyone repair Flex radios other than Flex Radio?

A local ham that I have an evening sked with on 75m (Paul, W0EBV) sent his Flex 5000 SDR transceiver to Flex Radio Systems to get it repaired a few months ago. However, it seems that Flex is either ...
2
votes
0answers
692 views

Blocking a specfic DMR ID

Is it possible to block a specific DMR ID Rx, sort of "ignore"? If so, is it repeater-based, or it has to be set locally, on radio? Speaking of popular md380/390 radios, there is a "Call Alert" ...
2
votes
0answers
154 views

It is allowed to have more APRS trackers with one callsign in Europe Union

I am interested if I can set up all my automatic APRS GPS trackers with one call sign in Austria (like in the US)? Are there any restrictions on usage?
2
votes
0answers
101 views

What protocol does the Vertex VX-2200/2100 use for programming?

I have seen a number of programming cable schematics on the internet, but I couldn't understand very much how they worked. From what I picked from all schematics, it appears the protocol uses the <...
1
vote
0answers
27 views

UK Intermediate training a not qualified newbie

I'm 99.9% certain that this will be OK, but independent verification would be reassuring. I am an "Intermediate" licence holder in the UK. This means that I am authorised to design and build my own ...
1
vote
0answers
43 views

HF propagation prediction using machine learning

Anyone out there know of or developed s/w to predict HF conditions using ML?
1
vote
1answer
53 views

Limit of transmission in GSM 1800 band

What is the limit of a transmitter in the GSM1800 band (~1830 MHz)? The ETSI GSM specification states a limit of -47dBm between 1GHz and 12.75GHz (https://www.etsi.org/deliver/etsi_gts/05/0505/05.00....

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