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Nyhetsflöde med senaste 30 inläggen från forumet

1. Using HR timer in CPU as VFO

   Some CPUs, such as STM32G474 and dsPIC33A, include HRTIM or HR PWM. I have been thinking that this hardware can be used with the internal PLL to function as a local-oscillator VFO in HF. In my understanding, it should certainly serve as an LO, and it can generate multiple phases for quadrature sampling detectors or mixers (QSD), push-pull power amps, and other purposes. But I have not been able to come up with how to make it good enough to call a VFO. The available frequency options are dense at lower frequencies but become very sparse as the frequency becomes higher.

   STM32G474's HRTIM can combine multiple timers to dither the periods to generate frequencies in finer steps, but that pattern is static and not based on accumulated phase error like the Bresenham method. Of course it lacks a ΔΣ modulator.

   QUESTION: Did anyone figure out how to achieve anything like a 0.1 to 0.3 kHz step using an HR timer in a CPU? I'm not looking for pretty 10 or 100 Hz steps; it can be quite irregular, as long as the good frequencies are dense enough and they are spectrally pure enough for radio use.

   I'll say this before someone does... MS5351 is cheap and versatile (it uses Bresenham), but it makes spurs, especially when the denominator of the fractional-N becomes large. I was trying to pre-select clean frequencies to use with MS5351 and live with coarse VFO steps (which are then compensated with NCO in the IF DSP), but when I saw HRTIM in STM32G474, I thought I could just use that... so please don't tell me to just put MS5351 on the board. It's always doable, but that just takes the fun away. MS5351 also requires a 3V supply, but STM32G474 runs on 1.8V, so we could finally have an HF transceiver that runs on two AA battery (such as it is). But in order to do QSD, fast analog switch is required, and 3.3V supply is minimum, better yet 5. At 1.8V supply voltage, the only RF/mixer/IF analog circuits I could design so far were a superhet, since I can use discrete transistors to make lower-noise amps than ICs, but that does not extend to an analog switch for QSD. Currently, I'm a bit more interested in pursuing a low-supply-voltage superhet version, since I don't think anyone has done that, and finally, the NE602 is gone, so there probably is a market for how to do a single super without it. Several QSD transceivers already exist, and they use MS5351 and require a 5+ volt supply.

   I'm also looking at CDCE6214 PLL IC, which also includes a 2nd- and 3rd-order ΣΔ modulator. It runs on 1.8V... supposedly. I'd hope it generates a cleaner spectrum than MS5351, but it appears that no one has published such a measurement.

2. How do I identify my station every 10 min. when operating on WiFi (2.4 GHz)?

   Popiel, Digital Networking for Ham Radio §7.17 "It's Good to Be a Ham" says:

   Hams can repurpose standard Part 15 commercial Wi-Fi devices and operate under Part 97. To operate a Part 15 device under Part 97, all you have to do is connect everything and operate under the standard Radio Amateur Part 97 rules: identify every 10 minutes, avoid pecuniary interest, don’t use encryption, and steer clear of any obscenity or pornography. It’s as simple as that.

   How do I identify my station every 10 min. when operating on WiFi (2.4 GHz)? Can I simply set the Service Set Identifier (SSID) to my call-sign?

3. Why is 30m limited to RTTY/data and 200W PEP?

   Why is 30m limited to RTTY / data and 200W PEP?

   From ARRL's frequency bands chart:

   

4. Does feed-line length affect SWR?

   Does the length of a feed-line have to be in fractions or multiples of wavelength? In other words: Does feed-line length affect SWR?

5. Why are some antennas good for receiving but not transmitting?

   The ARRL Antenna Book p. 13-17 says:

   Beverages have excellent directivity if erected properly, but they are quite inefficient. Therefore, they are not suitable for use as transmitting antennas.

   I've also heard discone antennas are excellent for receiving, even outside the bands they were designed to be good for transmitting.

   I thought there was a reciprocity law, that antennas good at transmitting are good at receiving and vice versa.

   Thus, why are some antennas good for receiving but not transmitting? Is this simply because the reflected wave would be dangerous for transmitter electronics at frequencies the VSWR is high and thus could damage the equipment?

6. What sort of political content can amateurs transmit?

   E1F08 [97.113(c)] says "Communications transmitted for hire or material compensation, except as otherwise provided in the rules" "are prohibited". Incorrect choice (B) is "Communications that have political content, except as allowed by the Fairness Doctrine", so it seems political content is permitted, but what is the Fairness Doctrine?

   What sort of political content can amateurs transmit? Can amateur radio be used for campaigning, endorsing candidates, and urging voters to vote for or against candidates, parties, or issues?

7. Is this a triangular roof antenna?

   I bet this Central Taiwan rack isn't an antenna at all. Seen just west of WGS84 24.169613, 120.69715. Google Street view, looks great on desktop, laptop. Rotation angle might be wrong when viewed on cellphone.

   In the center there are apparently two partially knocked over one ton water tanks. There is a wire in the foreground crossing the middle of the picture.

   Yes, one might think this antenna is similar to What kind of hexagonal antenna is this? , but 1) it has less sides. 2) is it really an antenna in the first place?

8. How does a Hilbert transform generate a SSB signal?

   Extra exam question E7F03 says "A Hilbert-transform filter" is a "type of digital signal processing filter … used to generate an SSB signal".

   How does a Hilbert transform used to generate a SSB signal? (and not, say, a Fourier transform?)

9. Does getting a ham license under FCC rules still require an US address to receive mail?

   I just tried, and you can register an FRN to get examined without a US address (the FCC online systems accepts a foreign address, and has "is a foreigner" as a reason to not state an SSN).

   However, a US-local club I'm working with on offering exams organizes its registration for the exam session through hamstudy.org, and that requires a US post address to be specified.

   However, I can't find nothing on the FCC website, nor on the interwebs / respective legislation that requires a postal address anymore – quite the contrary, the FCC seems to have gone fully paperless.

   So, is it just that hamstudy.org is behind on the administrative situation, or is a postal address still required to gain a US ham license?

10. Selecting inductors for Class E switching MOSFET power amplifiers (PA)

    I'm designing a Class E (switching) MOSFET power amplifier (PA) for a homebrew HF CW QRP transmitter, with target output 1 W - 5 W. I don't need to achieve actual Class E zero voltage switching efficiency; I only mean that my goal is to drive the MOSFET close to a switch, and filter out the harmonics with a LPF. I plan to use a IRF510 for the MOSFET.

    A key consideration here is the inductor that feeds the drain of the MOSFET. Most designs I've seen use hand wound toroid coils. I'd like to use mass produced inductors that can be bought on JLCPCB or the like. LTspice tells me that even 1 uH of inductance should be good for my needs; the more the better. But rough experiments seem to suggest these do not work well, perhaps due to things like ESR or self-resonance at high frequencies.

    Question: What type of inductor do I look for, in this role? There are zillions of premade inductors listed at Digikey or JLCPCB. How do I know which are good and which aren't? Is there an alternative to hand winding?

11. What headset will plug into id-51e Plus

    Would anyone know, What headset will plug into id-51e Plus?

12. Please explain antenna radio wave propagation diagram

    Most radio wave propagation diagrams that I have seen show the electric and magnetic fields as sinusoidal waves at 90 degrees to each other along a line 90 degrees to a monopole antenna, and the amplitude of the waves are equal to the height of the antenna. This always made me think the length of the antenna was proportional to the amplitude of the received signal, but science tells us that the length of the antenna is proportional to the best received wavelength. (I understand that the amplitude of a radio wave is proportional to the power of the signal)

    Is there radio wave propagation diagram that better shows how the antenna length is related to the wavelength of the best received (resonant) signal? Or are the radio wave propagation diagrams really only to show propagation patterns/directions of the electromagnetic fields and do not/cannot show the link between wavelength and resonant frequency antenna length?

13. Discrete-Component Mixer design

    I was building a radio receiver for FM waves (87.5-108MHz), I want to build every block on my own (oscillators, mixers, demodulators) and then put them together. I was now designing a mixer and i choose a Gilbert-Cell Mixer. I wanted to know

    1. If it's possible to build a Gilbert-Cell Mixer using discrete components and get it working on either a breadboard or a PCB
    2. Resources for design of Gilbert-Cell Mixer (I did try googling, but not sure which are the reliable sources.)
    3. Do you have any suggestions for other mixers that I could use?

    What are some problems I might face while implementing it in hardware?

14. APRS-IS filter by message sender

    I'm using KD0NKS' JS-based APRS-IS demo to query APRS-IS servers directly. I'm trying to only receive messages sent from my callsign using server-side filters.

    I've tried using a budlist filter (b/), type filter (t/), and group message filter (g/), but no matter which filter I use I only receive messages addressed TO my callsign, rather than from it. For example, I've tried 'b/N0CALL-7', 'p/N0CALL', g/N0CALL-7', and t/m/N0CALL-7/10000'(replacing N0CALL with my callsign in each).

    The parsed packets I do receive (for example, when I ping WXBOT for a weather update and successfully receive a message back) show my callsign-SSID as the value for the "destination" key. The "sourceCallsign" shows WXBOT, as expected for a received packet from the bot.

    APRS-IS server ("APRSSERVER" in the code) is 'rotate.aprs2.net'. Port is set to 14580.

    I'm using APRS-Fi to generate the messages, transmitting through my HT.

    Any ideas on which filter is the appropriate one to use, or how I can re-configure the filters to get the messages I'm sending rather than those sent to me? Thanks!

15. Yaesu ADMS-13 software: open saved file without reading config from radio first?

    I recently purchased a Yaesu FTM-6000. I like the radio, and I'm happy that the ADMS-13 software runs under WINE without a problem, but the software has some truly odd behavior and I'm wondering if I'm just missing something obvious.

    When you first start the software, it opens an empty document. The "Open..." menu item in the File menu is disabled, so even if you have a saved configuration, you can't open it to edit it/export it/write it to a radio.

    After reading the configuration from the radio successfully, the "Open..." item is enabled...so you can discard the configuration you just read from the radio and open a saved version instead.

    Is that expected behavior? I generally don't want to read the radio configuration; I want to update a saved configuration and then write it out.

    This is my first time working with Yaesu software, so I don't know if this is expected/typical behavior or not.

16. Testing a balun in isolation

    Consider a microwave RF source going to an unbalanced coaxial cable, then using a 1:1 balun to feed a dipole/Yagi style antenna. How can I test this 1:1 balun in isolation, independent of the type of balun used?

    The following diagram shows a proposed test mechanism:

    

    Case 1: Measure the RF power outputted from the coaxial cable, suppose this is x dBm.

    Case 2: Apply a balun to turn coaxial cable into 2 halves of a balanced line. Use the coaxial ground to create 2 short transmission lines and feed these into a combiner. If the balun is working as designed, summing the balanced line signals should cancel them out, and y dBm will be at the noise floor. Otherwise I should be able to measure how close to balanced the line is by comparing how low y dBm is relative to x dBm.

    At microwave frequencies I expect I will need to use phase-matched cables (or at least the same length of cable for UHF and below) for the 2 paths following the balun.

    Does this testing mechanism make sense? Is there a better way to test the function of a generic 1:1 balun?

17. Linking DStar repeaters using Icom syntax

    I would like to monitor a remote repeater (VE2RM) through my local repeater (VE3TTT). I am trying to figure out how to link them - specifically using the Icom ID-52A commands/syntax. I found some old posts which explain how to manually enter L and U commands in UR and RPT2, but I think there is a new way using Icom menu commands.

    I tried setting VE3TTT B as my FROM repeater, and VE2RM B as my TO repeater. But there is no "link" or "Unlink" possible. which makes me think I'm doing this wrong.

    I tried setting VE3TTT B as my FROM repeater, and VE3TTT G as my TO repeater. But there is no way to specify VE2RM B as the UR.

    Can someone explain how to do this using Icom menus?

    UPDATE: I called Icom support and was told this is not possible using the menus (in DR mode). I had to create three memorized channels to Link/Unlink/Use the repeater-to-repeater link. That seems crazy...even in DR mode I can't do it? I'm hoping he was wrong.

18. Can an antenna be affected if mounted to a bull bar?

    When I say 'mounted to a bull bar' I mean the antenna being metal on metal contact to the bull bar without any rubber or fiber glass keeping the materials from touching.

    • Could this affect the performance of receiving and transmitting a signal?
    • Does the antenna transfer current to the bull bar if there is nothing in-between?

    I ask since my mounted UHF radio isn't receiving anybody long range, whereas my handheld does.

    Extra info:

    My Mounted UHF radio is: GME TX3520

    Antenna: GME AE4702 6.6DBI UHF

    Handheld radio: Wouxun KG-UV8D

19. 14dB insertion loss for bandpass filter acceptable?

    I'm busy with a direct conversion receiver for the 20m band, using a VXO and a 14.060 MHz crystal.

    I designed a bandpass filter with the following components, using this design calculator.

    Someone gave me a nanoVNA to check the shape of the filter and after calibrating I got the following result.... The shape looks fine, but the insertion loss is -14 dB and the SWR 1.4. I wonder if this is typical and/or acceptable or if I can implement some improvements.

    Here is the Smith chart (I don't have any knowledge of how to read Smith charts)....

    

    And lastly a photo of the filter I built....

    

    Any comments and suggestions welcome.

20. MF band mixer - feasible parameters

    Trying to build an homebrew receiver for MF band broadcast (Navtext).

    Usually working on VHF, where all parts are easily found as an IC, but here I'm trying to get back to roots, so I may be missing something.

    I'm considering a superhet schema and up-counting the IF to reasonable values (7 or 9 MHz). However - here's my worry. The first-stage MF mixer would have really large difference between the input and oscillator ( 0.518 MHz and 8.482 MHz) and small difference between the oscillator and IF output. Would it work anyway? Is there a better option?

21. Mutual impedance of two parallel dipole

    Good Morning all,

    I want to calculate the mutual impedance of two parallel dipole.

    The first hypothesis is to assume that the dipole 2 is in open circuit, nothing difficult here I knew how to do it

    Hypothesis 2 is to assume that dipole 2 is short circuited or loaded with some impedance

    Are there equations for hypothesis 2, or is there a parameter to add or modify on Baker's equations?

    thank you

22. What is unique about a Low Noise Amplifier (LNA)?

    What is so special about a low noise amplifier? If I were to design an amplifier, I would always design an amplifier with low noise anyway.

    1. Why is it emphasised as being “Low Noise”?
    2. What are the design features that makes an amplifier “low noise”?

23. 50 Ohm Active Termination + Unity Gain Amp with PIIP3 > 60+ dBm

    I'm looking for a circuit topology that has unity gain, a 50 Ohm resistive input impedance, a 50 Ohm resistive output impedance, and here is the kicker, at least 60 dBm OIP3 over a 2 - 30 MHz HF bandwidth. I have tried a VMOS FET in a common gate configuration, and by adjusting the drain current to give a Gm of 20 mmhos, I get my 50 Ohm input impedance, but I only see 47 dBm of IP3. This circuit will terminate a Norton HF LNA preamp. Thanks for any suggestions - W6DSR

24. How does an E-Z-O Antenna work and why does it appear in Wikipedia's article on quad antennas?

    How are the conductors/radiators in the E-Z-O Antenna configured, and why is it described in Wikipedia's article Quad antenna?

    I see three circles and a spider web of wires inside each, but from an electrical point of view I can't understand what's going on, and the article doesn't help.

    How is this a type of quad antenna?

    below: Cropped, contrast enhanced, monochromed for better visualization of the wires. Original source.

    

    below: Original image click image for full size or visit link.

    

25. Is it legal to transmit scrambled or encrypted voice via SSB on ham bands?

    And also, can anyone tell me how? Using Arduino or any other way...

26. Reflection Coefficient to Impedance transformation on the Smith Chart

    A certain RF transistor has a source - reflection coefficient with a magnitude of .105 and a phase angle of 160°. When plotted on the Smith Chart, the normalized impedance is .825 +j .06 Ω. What is the actual or unnormalized impedance? What does it depend on? Is it 50(.825 +j .06 Ω) or 41 +j 3 Ω? Is the Smith Chart automatically normalized to 50 when dealing with RF transistor reflection coefficients that were derived from S - parameter equations and when determining the actual impedance the transistor wants to see?

27. What are some equivalents of a BF199 transistor?

    I'm planning to build an FM radio receiver using the instructions on http://www.instructables.com/id/Build-your-own-Crude-FM-Radio/

    The schematic uses a BF199 transistor which is marked "obsolete" by some component suppliers. What would be a current and widely available equivalent?

    I tried to search at my preferred shop, https://www.rs-online.com using the following properties:

    • Si NPN RF Transistor
    • Vcb max 40V
    • hFE min 38
    • ft 1100 MHz
    • Pc 350 mW

    And did not find anything suitable.

    The original data sheet is here: https://www.mouser.com/ds/2/308/BF199-1118776.pdf

28. Term For Receive Antenna Using Lorentz Force?

    Since:

    $$\vec F = q \left(-\nabla \phi - \frac{\partial \vec A}{\partial t} + \vec v \times \left( \nabla \times \vec A \right) \right)$$

    It would seem that a receive antenna with a current density J whose velocity field was v would produce enhanced reception. Is this correct? If so, there must be a technical name for this kind of antenna. What is that name?

    Note: I chose the potentials description of the Lorentz force equation to expose all components of the EMF in a single expression. Conduction band electrons of the receive antenna are experiencing a force that changes with time resulting from the incident EM wave. I understand that $-\nabla \phi = 0$ when Tx and Rx are exactly parallel and orthogonally positioned.

29. What is the impedance of an end-fed half-wave antenna?

    It is my understanding that the feed-point impedance ($Z_a$) of an end-fed half-wave antenna is dependent on at least the following factors:

    • $L_a$: The length of the radiating element of the antenna.
    • $D_a$: The diameter of the radiating element of the antenna.
    • Environment surrounding the antenna.

    It it also my understanding that such an antenna is not actually resonant (Meaning the impedance is purely resistive) when $L_a = 0.5\lambda$, but rather something a tad smaller. A common number I've seen thrown around is ~$0.41\lambda$, but different sources seem to have slightly different values.

    My general question is, assuming the antenna is radiating in free-space, what is the theoretical mathematical relationship between $L_a$, $D_a$, and $Z_a$?

    More specifically, I'd like to know how to calculate two things:

    • For a given $D_a$, what value of $L_a$ (when $L_a \le 0.5\lambda)$ would give me a real (purely resistive) $Z_a$ in free-space?
    • For a given $L_a$ and $D_a$ (or when those variables are constrained so that $Z_a$ is always real), what is the exact value of $Z_a$ in free-space?

    Bonus points for elaborating on how these values are related in practical, non-free-space environments.

    I have seen many confusing estimations for $Z_a$, ranging between 1800Ω and 5000Ω, which is a huge range. I want to better understand what factors are involved and how to mathematically calculate the value under ideal circumstances.

30. Morse code help

    http://vocaroo.com/i/s0fsMOJ82A7k

    Trying to decipher this morse code if someone can help me. It's 14 characters long and the first lot is Illuminatih I think.