Unanswered Questions

182 questions with no upvoted or accepted answers
9 votes
0 answers
412 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 ...
7 votes
0 answers
602 views

Simple AM receiver with gnuradio / RTL-SDR

EDIT: I have succeeded in getting the AM receiver to work, by replacing the AM Demod block with a Complex To Mag, and a Band Pass filter (this is noted as an alternative in the AM Demod docs). ...
6 votes
0 answers
56 views

How does Large Loop Antenna work physically?

I am learning about loop antennas at the moment. I read that the respone of a small loop Antenna is propotional to the rate of change of magnetic flux through the loop which causes a uniform current ...
6 votes
0 answers
220 views

Hardened UHF Antennas

Minuteman missile silos used an interesting hardened UHF antenna. What kind of antenna is this? Does anyone have a drawing with a cross section? Edit: Jay Moore added a picture to a different type of ...
6 votes
0 answers
211 views

How to estimate input and output impedance of an amplifier?

I'm trying to figure out how to design power amplifiers which input and output are properly matched to 50 Ohm. My thinking was that the most bullet proofed approach would be to model an amplifier in ...
6 votes
0 answers
174 views

Choice of PCB coil design for filter inductor at ca 20 to 400 MHz, 5 W

Looking at the diplexer schematic from this nice question, I realized this can completely be done in PCB-formed elements (minus the connectors). (As a kind of counter-action to the original question'...
5 votes
0 answers
407 views

What is an expected IF level of SA612?

I tried to use SA612 as a frequency mixer. Since it's a Gilbert cell, it has a high input impedance. Thus I added a pair of transformers as "Experimental Methods in RF Design" book suggests: ...
5 votes
0 answers
115 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 ...
4 votes
0 answers
98 views

Checklist for QRO remote setup

In a few weeks I'm hoping to set up a solid state linear amplifier at a remote shack that I've set up at the house of a friend who lives in a rural area. I've been connecting to this shack remotely ...
4 votes
0 answers
442 views

4NEC2 radials & grounds

Teaching myself 4NEC2 and have most of it under control, which is good. Regarding radials & grounds, i've been learning the "rules" NEC(2) has, summarised below. 4.1. Free space. In the ...
4 votes
0 answers
146 views

Problem with theory of HF detector

I'm currently trying to build my own SWR power Meter. This design is based on the so known HT detector with schottky diode BAS70. For my understanding, and for easy purpose, I'm currently focusing on ...
4 votes
0 answers
82 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
0 answers
100 views

Building Antenna Trap: Highest impedance/lowest capacitance/greatest # of turns?

I made my first multi band antenna this weekend for 20 and 15 meters for an EFHW wire with a 49:1 unun, to be used with 5 W rig. I used a toroid I had on hand, T80-2. I hang this antenna in my living ...
3 votes
0 answers
72 views

Turnstile antennas with a "single-point feed": what's the antenna theory behind this, and how do I build/model it?

The conventional turnstile antenna uses a 1/4wl phasing line between the crossed elements, to get the required phase shift. 4nec2 includes an example file, though, of a circularly-polarized Yagi using ...
3 votes
0 answers
48 views

Radio Service Software Motorola Syntor x9000

My name is Roger, I live in Sweden, have bought some old motorola synths x9000 transceivers that I need to reprogram, but have great difficulty finding the Rvn 4007E software as it should be. Have ...

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