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128 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 ...
134 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 ...
138 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 ...
605 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 ...
56 views

How to measuring ferrite core efficiency vs frequency

There is an unknown ferrite toroid. I would like to figure out whether it can be used in an audio transformer, or maybe in a 1:4 transformer on given HF frequency. The experiment I came up with is ...
64 views

Heathkit SB-102 Plate Current out of control

I bought a "technician special" Heathkit SB-102 transceiver. Everything seems to work well until I attach a dummy load and try to go through the "initial tune up" procedure in the manual. At the ...
64 views

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 ...
62 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 ...
213 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 ...
43 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 ...
40 views

What dot means in JTDX FT8 received messages?

What dot near country means in JTDX? Maybe LOTW?
34 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-...
66 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 ...
39 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 ...
76 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. ...
92 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 ...
172 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....
781 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 ...
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 ...
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 ...
144 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 ...
38 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 ...
57 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 ...
32 views

Fetching data from APRS-IS.net

I would like to fetch the data transmitted by a specific radio station from APRS-IS.net servers. I've read the documentation on their site and it is not clear how you would do it, if you are fetching ...
77 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 ...
53 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 ...
57 views

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 (...
74 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 ...
155 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 ...
282 views

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 ...
64 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 ...
30 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 ...
207 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 ...
429 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 ...
306 views

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 ...
645 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" ...
150 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?
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 <...
32 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 ...
34 views

Why is self-resonance important in a loop antenna?

I visited a "small loop antenna" calculator web site today and fed in my horizontal loop gepmetry, curious to see what it would say. 2" dia wire, 72' circumference, 3.935MHz. Interesting results, ...
65 views

audio problem with SDR on MacOS

I'm experimenting with SDR on MacOS High Sierra. Trying both CubeSDR and GQRX and experiencing similar issues with both. The applications seem to work, but the audio is choppy and chipmunk-like. ...
60 views

Compare signal strength with Software Defined Radio

I want to compare field strength with an RTL-SDR dongle or HackRF One. With comparing I mean being correct relative to one another, like if I know field strength of one in mW/m^2 then I know the other....
41 views

How to connect MX614 to an ATmega 328p and a DRA818V to make an APRS transceiver

I am in a process of making a nanosatellite on which I am considering putting an APRS digipeater. I know about micro-modem based on ATmega 328P but it is pretty power hungry. MX614 has really good ...
18 views

How to identify the mic connection pins in Heathkit SB-102?

One of the things I need to do to put my Heathkit SB-102 into service is connect a microphone. I've got a suitable crystal mic, with four conductors in the cable -- two for the mic element, and two ...
38 views

Error in an attempt to simulate SDR frontend hardware in GRC

I was reading these lecture slides: https://web.mit.edu/6.02/www/f2006/handouts/Lec9.pdf and I tried to implement some of the schematics shown there in GNU Radio. On page 3 the author describes how ...
29 views

uhd_packet_rx do not work

I was trying to set up packet communication using examples in gr-digital/examples/uhd_packet_tx and rx. uhd_packet_tx is doing fine, but on receiver side(uhd_packet_rx) is freeze when i check up the ...
70 views

Capturing Bluetooth / WiFi on an SDR

I have a question, right before purchasing SDR for some tests: Commercial hardware for bluetooth (even Ubertooth) allows you to receive packets on a 1MHz channel. Which practicaly means that if you, ...
93 views

communication with underground mines?

I have a meter that will analyze limited RF spectrum in my area. One frequency that keeps coming up is 2.498 kHz. An FCC site listed that as the frequency used to communicate with underground mines. ...