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Nyhetsflöde med senaste 30 inläggen från forumet

1. What can you do to prevent exposure of RF?

   When I bought my transceiver, I found out that it only puts out less than half a watt (which can't travel a 1 mile radius from the antenna). So, I bought a power amplifier. It says it amplifies it to 75 watts, but I think maybe that's a little too many watts for a human to be 1 foot away from the antenna. So, what can I do to make it safer for me to be around the antenna? I read that metal deflects radio waves, so should I make a metal shield to protect myself? Or is transmitting 75 watts on HF is too little to do damage? The antenna is a EFHW antenna.

2. What is the antenna design and gain for the WA1 U/V band antenna on the ISS?

   My son KJ7NLL is working to contact the ISS using an antenna we built together, and we were wondering the approximate minimum transmission power to reach the ISS. If I understand correctly (and correct me if I'm wrong), roughly speaking, we need to solve for tx_power from the following equation (in dB) to estimate the minimum tx_power:

   • tx_power - feedline_loss + tx_antenna_gain - path_loss + rx_antenna_gain + (-rx_sensitivity) = 0

   The Kenwood TM-D710GA onboard the ISS has a sensitivity of 0.16uV (which we think is -122dBm if we did the math right). Our 2m helical antenna gain is ~13dB and path loss to the ISS when directly overhead is ~127dB (of course, we need more than that when near the horizon, but not sure what that distance would be).

   The ISS has a series of "WA" antennas, but we have not found the gain specs.

   • What are the gain specs (and patterns?) for the ISS U/V antennas?
   • Is our math right?

   These are the ISS U/V Amateur Radio antennae pictured from this PDF:

   

3. Take The HAREC exam in spain in english [duplicate]

   I am looking to take the HAREC exam but I have a dilema, I currently live in Spain and my Spanish language skills are not that great... I was wondering if I can take the HAREC exam online with a Spanish translator sat next to me or if I can take it in English through one of the Irish test centres even though I live in Spain. Would appreciate any help on this subject.

4. How do you decide on number of turns for twisted gamma match?

   I'm looking at a 40MHz short transmitting loop (STL) with 6 rectangular loops: I need to fit within some design parameters and this gives the good radiation that I need in the near field.

   If I want to feed with a twisted gamma match then should the loops of the gamma go around all of the antenna current loops or just one?

   I'm also confused about how many loops.... The modelling code says about 0.1 ohm radiation resistance and 0.1 ohm "ohmic" resistance, which I can live with..

   So if I want a twisted gamma with 50 ohm coax feed, does that mean that I need 250 twists to make the gammma-ray match?!

   The devices that I see discussed on the internet seem to have 5-10 twists.

   I'm confused.

   Thanks, T.

5. Why are the signals that my antenna is receiving weak? [closed]

   I recently bought the EFHW antenna kit from ARRL, put it together, and set it up. But, my received signals were not clear enough to hear clearly. Is the problem specific to the antenna from ARRL, my equipment, or I built it incorrectly? I tried every HF band, tried it at daytime, and the lowest point above ground was 1/2 of a foot.

6. Optimal antenna configuration for edge-on power transfer

   I need to build a MHz antenna that can power an RFID chip that responds to mag field perpendicular to the plane of a loop antenna, e.g, using STL transmitter with a small receiver loop in same plane as the transmitter. I'm confused about the benefit of extra turns on the transmitter.

   For a given a loop with area $A$ and perimeter $C$ then I can estimate a radiation resistance per unit area (for one coil) $R_{r0}$ and radiation loss per unit circumference, $R_{l0}$. Assume that I have a capacitor to cancel out inductance at resonance, then I only need to worry about total resistance which seems likely to be $R_{r0} A^2 N^2 + R_{l0} C N$. Regardless of efficiency, then $P_{in} = I^2 R_{total}$ i.e. $I^2 N^2 A^2 (R_{r0} +R_{l0}*C/A^2/N)$. I think the mag field in the plane parallel to the loop is (for small transmitter loop) $-\beta^2 I N A \exp(j \beta r)/r$.

   Putting that all together says that for fixed $P_{in}$ then assuming that I can always impedance match then I should try to minimize $R_{r0} + R_{l0} C/A^2 / N$. I.e. increase as many turns as I can and prefer circles to decrease $C$ relative to $A$.

   And then with regard impedance matching, if I can crank up $N$ then I can make $R_{total}$ equal to 50 ohms, or whatever I want.

   So why do STL's usually have just one or two loops?! Or did I make a mistake in the math...

   One potential mistake that I see is that I do need $NC$ to be less than $\lambda /3$. So for a circle set $N = \lambda /3/(2 \pi r)$ and then minimize $R_{r0}+R_{l0} 12 \pi^2 r^2 / \pi^2 / r^4 / \lambda$.

   Ah... so you set $N=1$ to make $r$ as big as possible. Did I get it right?

   But if $r$ is constrained for some reason then you should increase $N$ until $NC = \lambda / 3$. Yes?

7. How do you make a HF contact?

   I asked google, but I had no luck. It didn't say anything about what you should say in a contact. It only said how you should start a contact. Also, I have heard that you are supposed to give a RST report at the beginning of a contact, but how do you do it?

8. Getting My First Radio(Transceiver) [closed]

   I'm a prepper based in Pakistan, currently exploring communication options for grid-down scenarios. My recent discovery of ham radio has sparked my interest, both for preparedness and as a hobby. At present, I possess a Bench KH2028 receiver for FM, LW, MW, and SW frequencies. Now, I'm seeking a transceiver that meets specific criteria: compact, lightweight, energy-efficient, dependable, user-friendly, requiring minimal accessories, and most importantly, capable of facilitating global communication.

   In Pakistan, the scarcity of amateur radio operators means limited access to repeaters and nearby counterparts. Based on my preliminary online research, UHF and VHF might not be as useful, though I could be mistaken. I'm willing to make a one-time investment in a substantial radio system alongside some inexpensive HTs. I'm open to suggestions regarding bands, modes, or any viable alternatives.

   The Icom IC-705 caught my attention, but I'm eager to explore other recommendations that might better suit my needs. Additionally, I'm seeking antennas that align with similar criteria: small, lightweight, energy-efficient, reliable, easy to set up, requiring minimal accessories, and capable of enabling effective communication. Remember, in Pakistan, our radio infrastructure is limited, and my goal encompasses regular use, communication during grid-down scenarios, and emergency relief efforts. Ignore my technical mistakes due to lack of radio knowledge

9. Operation of an off-center fed vertical for 10 meters

   I am looking for a smallish omni-directional 10 meter antenna for installation in my attic. I notice that MFJ sells one called MFJ-1790. They call it an off-center fed vertical, and it has two horizontal radials. The length of the vertical element is 11 feet which is about about 5/16 wavelength at 28.4 MHz. So it is slightly longer than a 1/4 wavelength vertical.

   https://mfjenterprises.com/products/mfj-1790

   I was thinking of modeling it, and maybe trying to build one using wire, but I don't know how to feed it. There was a review of one of these, and from that you can see use of a toroidal choke at the base but nothing beyond that (the picture was to show a fatal assembly error lol).

   https://www.worldwidedx.com/threads/a-look-at-the-mfj-1790-portable-10-meter-vertical-antenna.162599/

   I can't find much on off-center fed verticals. Any idea if this a known design, and how you would feed it?

   By the way, I am currently using an outdoor "stealth" ground mounted 1/4 vertical wire with ground radials, quite near to my house. It works OK, but I am wondering if I can get something elevated (about 18-20 feet) I will get better performance. The alternative it to build a 1/4 wavelength ground plane which is a lot easier, but maybe less performant.

10. Find the the geographical North for yagi setup

    I am setting up a 435MHz cross polarized yagi antenna on Yaesu rotor (for both azimuth and elevation). The application is satellite tracking. The beamwidth of my antenna is 20 deg horizontal and vertical.

    What is the best way to find the line pointing towards geographical North (or true North, that can be calculated using a formula) from a location for the initial setup? Indeed, compass is one of the options, and I tested locally bought two - three analog and digital compasses. They have almost 4-5 degrees offset with respect to each other. Even the same with my mobile phone compass.

11. Statistics on ham operators age, internationally

    Are there statistics that cover more than the USA regarding how the age of

    • licensed amateurs
    • members of national ham organizations

    is distributed? All I get are questionable sources on the internet for average ages, but I'd actually be interest in age cohort data, e.g. more a proper curve for ages 5 to 99.

    I'm especially interested in numbers for

    • Germany
    • France
    • Belgium
    • Japan
    • BRICS nations
    • Commonwealth

12. Why not access the AO-91 satellite at night during eclipse?

    According to amsat-uk.org, the AO 91 satellite should not be accessed during eclipse because it is near EOL.

    • AO-91 (RadFxSat / Fox-1B) Near end of life. If you find it on, do not attempt to access in eclipse! (That is, don't use it at night)

    I'm happy to play by the rules, but I'm curious: What about it getting old precludes it from use in the dark?

13. High SWR at full height

    I operate a low power FM radio station. I have always had issues with high SWRs. Recently I have purchased a new transmitter, new antenna, and new 100 ft cable from the same company assuming they would work well together.

    To test the system, I mounted the antenna as high as I could reach on my radio tower (about 5 feet). I had no trouble broadcasting at 100 watts at 5 feet.

    I am in a very rural area, so it took some time but I found a tower climber to come out and mount my antenna on top of my tower. Now the antenna is at a height of 75 feet. Same antenna as at 5 feet, same cable, same transmitter. However, now that it is at 75 feet when I go above 30% power or 30 watts my SWRs become too high and the transmitter shuts off to avoid meltdown.

    Any idea why it would work just fine at 100 watts at 5 feet, but won't operate above 30 watts at 70 feet? Could something be wrong with my tower?

14. Are there any stations other than W1AW that fall under 47 CFR 97.113(a)(3)(iv)?

    47 CFR 97.113(a)(3) normally prohibits amateurs from transmitting

    [c]ommunications in which the station licensee or control operator has a pecuniary interest, including communications on behalf of an employer.

    However, 47 CFR 97.112(a)(3)(iv) allows

    [t]he control operator of a club station... [to] accept compensation for the periods of time when the station is transmitting telegraphy practice or information bulletins, provided that the station transmits such telegraphy practice and bulletins for at least 40 hours per week; schedules operations on at least six amateur service MF and HF bands using reasonable measures to maximize coverage; where the schedule of normal operating times and frequencies is published at least 30 days in advance of the actual transmissions; and where the control operator does not accept any direct or indirect compensation for any other service as a control operator.

    This seems to basically be a long-winded way of saying "W1AW operators can be paid to send code practice," without naming a particular station. Are there any stations other than W1AW that meet these requirements?

15. I get no audio on my new Quansheng uv-5r plus despite green receive light

    Quansheng uv-5r plus. First time on these devices, sorry. The receive light goes on but no receive audio. Transmit on ht works fine. Audio from device prompts are ok. Checked frequency traffic with another ht and found no issues. Is there a squelch control on this device?

16. Measuring Power - Attenuators and 50 Ohm Termination

    I'm attempting to measure the output power of my transceiver + linear amp combination and I would like to confirm that my measurement approach is correct. I need to get the output power down to a level that's safe for my spectrum analyzer.

    In particular, I need to confirm that I should terminate my attenuation chain with a 50 ohm load and it's OK to measure across the dummy load with my oscilloscope probe in high-impedance (x10) mode (my scope doesn't have a 50 ohm mode).

    I get confused sometimes and reason that 50 ohms in parallel is 25 ohms and that doesn't seem correct. However, I'm guessing the amp "sees" 50 ohms and as I understand it, the attenuator must be terminated in 50 ohms to achieve its labelled attenuation. So, maybe it's when you look back into the 50 ohm loaded attenuator chain that you see 25 ohms (i.e., from the scope) and maybe that's OK. Or maybe it's not? That's my confusion.

    EDIT

    I believe the large attenuator performs well in the HF frequency range based on previous measurements. Simple tests at DC show it's certainly a 50 ohm in/out attenuator.

    The purpose of all this is to understand the impact of placing a homemade low-pass filter after the linear. For that, I intend to use the Tiny SA, but since I'm not sure what the output power of my amp is, I'm cautious to measure the attenuated output with an oscilloscope, which has a high impedance input and an overall better tolerance for gaffs as I experimentally reduce the signal power to a desired level.

    As I understand it (but I may be incorrect), the Tiny SA would like a -25dBm input signal, so I'm aiming for this level.

    Finally, I'm not looking for pin-point accuracy here. I realize the oscilloscope has its own tolerances and the cabling and all the rest of it will introduce errors. Not to mention the fact that the attenuators themselves probably aren't perfect. What I'm more concerned about is making a measurement that's fundamentally wrong and I end up calculating substantially more or less power than I actually have.

    Here's a schematic picture of the exact measurement setup. Frequency is around 7MHz or 40m band.

    

17. Using Aviation VHF radio on different frequencies

    I have an old Icom A-5 aviation handheld with a frequency range of 118.000-136.975 MHz on top of WX, AM, and FM receive functions. Is there any way with little modification, or a simple static build that I can shift my frequency range to encompass marine radio? Specifically from the 156.050-157.425 Mhz range. I am looking to use it to listen in on my local airports, but would like the option to listen to my local port operations, and talk to friends at my sailing club from home if i can push the transmit range that far.

    Edit: thanks for all the helpful responses, I have decided to build a Yagi for the avband, to continue listening, and I am taking my technician test tomorrow. I know how important it is not to transmit on avband, I am a student pilot, and my dad gave me the radio. I am getting a UV-5R to use once I get my callsign.

18. Wave bounce inside a resonant antenna

    Let's assume we have a transmitter, a feed line, and a standing wave antenna (dipole, etc.). The transmitter is matched with the feed line, and the feed line is matched with the antenna, which is why the traveling wave in the feed line does not reflect from the antenna's feed point and passes without any obstacle. That is, there is no standing wave in the feed line, and this is good (radio amateurs appreciate this).

    Now our antenna creates a standing wave. But if the wave doesn't see an obstacle when it moves towards the antenna, why doesn't the same happen in the reverse direction, when the wave goes from the tip of the antenna and reaches its base? Why does the wave bounce multiple times inside the antenna and why it doesn't move back into the feed line if there is a perfect impedance match at the base? Yet a standing wave is still created in the antenna. The question is, how?

19. Suggestion for the RF cable

    I am setting up a HAM antenna (50 ohm) on my house terrace. The cable length is going to be around 25 meters from terrace to my transmitter. Which type of co-axial RF cable should I choose with low signal attenuation (practical) in mind? For example, RG-6, RG-8, LMR types...

    Frequencies - 145MHz and 433MHz. Maximum power that I would transmit is 500W. Budget is not a problem but please do not suggest superconductor based solutions ;)

    PS: I am just asking for the type of cable to be used in general.

20. Programming cable doesn't recognise Quansheng UV-5R Plus

    I am trying to program my Quansheng UV-5R Plus with a Baofeng cable. The cable works on my Baofeng, so I know it is OK. I'm told on the website to treat the UV-5R Plus just like a UV-5R but what I get when I connect my radio, using Chirp, is "Error communicating with radio". "Header short read".

    I am holding the programming cable in tightly, as suggested in the answer to another similar question on this site, so I am pretty confident that is OK.

21. What was the first QSO by an astronaut? Was it code or voice?

    Discussion under this answer to Could amateur radio operators or others contact the ISS against NASA's wishes? in Space Exploration SE explore some activity from the Mir and ISS stations and the Space Shuttle, but I'm curious about the first proper Ham to Ham QSO by an astronaut who was in space at the time.

    If an answer can cite known "firsts" for both code and for voice separately, that would be even better.

    update: I just discovered that I'd asked three years ago a different but related question in Space Exploration SE. However, QSO's were not mentioned in the question or its answers.

    • First Ham Radio contact from space; what frequency, what kind of antenna, and how did they route the coax out the window?

22. Cannot connect Quansheng UV-K5(8) with programming cable

    I bought a Quansheng UV-K5(8), and I am impressed by the audio quality, there appears to be a better ratio of signal to noise out of the speaker on listening, and it's a nice little radio, though with some quirks.

    I also bought a Baofeng programming cable that is promised will work with the Quansheng UV-K5, which is in every sense the same as my Quansheng UV-K5(8).

    However, while the cable works with my Baofeng UV-13 Pro perfectly, I cannot get it to programme the Quansheng UV-K5(8), the software will not connect to the radio.

    I have tried both MacOS Montery and Windows 10. The Baofeng UV-13 Pro works with its proprietary software on Windows 10 so the cable works.

    On both systems, plugging in the cable finds the USB-to-Serial chip and creates the serial port, but there is no possibility of connecting to the Quansheng, I tried for hours on both systems, trying Chirp, generic drivers, hideous Quansheng USB drivers that only work if you set your Windows display language to Simplified Chinese, Quansheng provided firmware flash tool (Just to try to get something to connect) but it is impossible to connect the Quansheng radio on either system.

    I'm almost certain it's the right cable, I'm very certain it works, the radio works in every other way, so I'm thinking something like:

    1. The cable works with Baufeng UV-13 Pro, and is advertised to work with Quansheng UV-K5 but doesn't work with Quansheng UV-K5(8), I think this very unlikely;

    2. The radio is broken in some way;

    3. The Quansheng-provided driver for Windows 10 and the generic driver for the USB to Serial on both Windows and MacOS somehow don't work;

    4. The serial port settings (Buad, parity, stop bit, etc) are different for the Baofeng that works and the Quansheng that doesn't, but nobody on the internet seems to have documented this, so it's unlikely.

    I can't find a more suitable cable online, Please I need any help or ideas!

23. How do you hide the waterfall scope in an Icom IC-705 and display just the meters?

    I've seen the display in that mode but I'm failing to reproduce it. Any ideas how to hide the waterfall scope entirely (not just make it smaller)?

24. What type of metal, length & diameter should i use to build a vertical antenna to listen to airband frequencies (118-137Mhz)?

    I recently purchased RTL-SDR v3 dongle along with antenna kit. I used 60cm each length and built vertical dipole antenna with boom length of 58cm and listened to airband frequencies.The closest airport from where i listen to is almost 15kms away. The audio received is with a lot of noise. Hence i have decided to build an antenna for permanent installation almost 30ft above ground.

25. Transmitting high-speed PWM over RF

    First, let me apologize in advance if this isn't the correct exchange to post this question on.

    I have a 50 MHz PWM signal (it's actually a 50 MHz 50% DC clock with a 1PPS clock embedded with PWM) that I would like to transmit over the 2.4 GHz ISM band with as low latency as possible. My original thought was to digitize the clock with a high-speed ADC, then stream the samples to GNU Radio and transmit via SDR, then recover on the receive side and playback the samples with a high-speed DAC. The problem I'm running into is that the only capture cards I've been able to find capable of running at the sample rate needed (>500MS/s) and streaming in real-time to GRC are prohibitively expensive ($8000+).

    My question is, is anyone aware of any alternative methods of transmitting the 50 MHz PWM over ISM? I would be willing to entertain a different method of streaming to GRC or an entirely different setup. I don't know of any radios that could take the signal as input directly and transmit it, then receive it and output it directly, but admittedly I am new to the world of RF so it's possible there's a solution that exists that I'm simply unaware of.

26. How to send DMR SMS using MMDVM modem or hackrf?

    I have a baofeng DMR radio with SMS feature, and since there is not much DMR radio owners in my area I want to do something myself.

    The easiest thing I can do I thought is to send myself some SMS as I did with a POCSAG pager using my hackrf one.

    But I haven't found any software to do that. All I found is MMDVM-SDR program on github which acts as a MMDVM modem utilizing a fake serial port. It allows to get commands from the MMDVM-Host and modulate them as IQ WAV file.

    There is one problem: that MMDVM modem protocol has no commands to send DMR SMS. It only accepts "DMR DATA packet" at different rates. I tried to google for "DMR AIR interface" but it also has no mentions of SMS.

    By that time I learned that DMR SMS is a non-standartized thing which leaves me with this questions (one is part of the another):

    • What format all those TYT and Baofeng radios is using, where I can get it's datasheet.
    • How to make a DMR SMS packet for my radio and send it to a MMDVM modem emulator or directly to the SDR using some other modem software?

    PS: I tried to record my radio's signal with SDR and play it back. With voice it works, I can hear myself, but with SMS it doesn't work for some reason: my radio just ignores them (maybe that is because it's number in both from and to fields?)

27. FLDigi Crashes When Trying to Load RigCAT Description File

    I am trying to setup FLDigi with my ICOM-7300 via the USB connection so I can start using digital modes. Everytime I try to follow the instructions here, it doesn't work. Specifically, everytime I try to load the .xml file, FLDigi hangs up and crashes.

    

    I tried using the Hamlib definition for the radio, and I can see it has made some kind of connection because whenever I rotate the VFO on the radio, the FLDigi frequency display changes, and vice versa when I change that frequency the radio changes.

    However, I am receiving nothing on the waterfall display, and when I center on digital signals in the low end of the 40m band FLDigi doesn't decode anything. Not even a garbled signal that might indicate I'm on the wrong encoding protocol.

    What am I doing wrong, and what do I need to do to get the radio data into FLDigi in addition to the rig control features?

28. Slot antenna for 2 meter mobile

    My primary vehicle is a Smart car, with a roof that's a piece of plastic(100% moon roof). Not the most awesome of cars to use for grounds. I'm building a bumper mounted antenna tower, EMT with some square tube. Earlier today I stumbled across an article on 2 meter slot antennas cut in to satellite dishes. Literature is repetitive either directed towards that subject or TV and UHF broadcasting. I like the idea of a Dipole analogue that doesn't look like an antenna... Currently the 1/2 wave whip makes it look MORE like a cheap RC toy...

    This isn't a basic theory question, more of a practical application...

    So the questions are:

    Would a Slot antenna cut into a piece of 1.5 inch wide, 1/8 inch thick bar stock work? Minimal expense and I can get it almost anywhere.

    Would that be better than just cutting the slot into the bars? I can't find out if that's very directional, I assume I'd cut it in the top and use weep holes, cheapest option.

    Any better Ideas?

29. What is the output impedance of a typical solid state ham transmitter?

    I've often heard that the output impedance is 50Ω, and the load impedance should be matched to that and also 50Ω. While the reasons for the load impedance to be 50Ω are clear, is the output impedance really 50Ω and if so why? If it isn't 50Ω, what is it?

    Wouldn't this mean a large amount of power is lost in the transmitter? Wouldn't it mean SWR losses would be much higher than they actually are?

30. What is the peak voltage at the tips of a dipole antenna?

    What is the peak voltage present at the very end tips of half-wave dipole antenna in free space, and how might this peak voltage relate to transmitter type, transmitter power, RF frequency vs. antenna half-wave frequency mismatch, feed line, SWR, wire diameter, and etc.