Hot answers tagged

18

The bits per sample will affect the dynamic range of your receiver. There's a lot of math that I'm sure you can find, but here's the intuitive explanation: A digital signal can represent only discrete quantities, where an analog signal can represent infinitely many quantities between any two discrete quantities the digital signal might represent. The ...


17

Receive antennas are the easiest thing ever. You just need two things: something that conducts electricity another thing that conducts electricity Attach one to the center contact on a BNC connector. Connect another to the shield. Boom, done. If you can't find two things, then one can be the Earth. Alternately, you can use two ends of one thing that ...


16

If you are interested in the electronics and technical aspects of transmission and reception, then yes, now is a fine time to get involved in building your own radios. If you are more interested in pursuing communicating with other users, though, your time and effort would be better spent using a good rig. Now is also a great time to get into Software ...


12

I suspect the primary reason that the kit supplier does not ship the kit with prewound toroids is that there is insufficient volume to make it economical to have them commercially wound. A second possibility is that the kit supplier views winding toroids as a desirable part of the kit building experience. A third possibility is that the kit supplier is ...


11

Homebrew is (as the name suggests) when you make your equipment yourself, as opposed to buying it. An amateur setup consists of many components - the largest and most complicated of which are a radio transceiver (or separate receiver and transmitter), and the antenna. A power supply is also needed, but these are relatively inexpensive compared to the cost ...


10

The first AM transmitters were made by hacking the power supplies of CW transmitters. Replace the 9V battery with a variable voltage source and you have yourself an AM transmitter. Not an especially great one, but if simple is your primary concern, it can't get much simpler. There are many ways you might do that, but if "simple" means "low parts count", ...


9

The results depend on the two bands you choose. Frequency ratios of 2:1 are a good choice because the longer dipole, which is a full wavelength at the higher frequency band, will show high impedance on that band, while the shorter dipole, which is only a quarter wavelength at the lower frequency band, will show a high (capacitive) impedance on that band. ...


8

I am not sure if you are asking about converting a CB walkie-talkie to 10m or building one from scratch so I will address both, not feeling like working at the moment: Converting a CB walkie-talkie What it will take to Convert a CB walkie-talkie is going to depend on how it's contructed, of course. It can be as simple as replacing one or more crystals. A ...


8

Executive Summary Assuming: air dielectric (insulator) 50Ω characteristic impedance Then for round coax, make the inside diameter of the outside conductor 2.302 times larger than the diameter of the inside conductor. If the shield is square, and the inner conductor is still round, make the inside length of one side of the shield 2.134 times larger than ...


8

Just about anything connected to your feedline makes an antenna. A lot of the concerns in transmitting antennas (low SWR, high efficiency, etc) are of diminished importance for receiving antennas, so it's surprisingly easy to make a perfectly good receive antenna with very little design effort. You don't necessarily need the antenna to be resonant or "tuned"...


8

Some things are best answered in Song. I don't want to encourage you, but you might hum along to the tune of Eye Of The Tiger: It's the wind of the donut It's the thrill of the built Rising up to the challenge of our fingers And the last known capac'tor puffs its smoke in the night and he's watching us all with the eeeeeye of the winder No, ...


7

Take heart, there are some diehard AM operators out there on various bands. I am not one of them, but I have seen messages about skeds and frequencies for them. I am not really sure how you can AM that circuit specifically. I suppose you could substitute the mic input from the usual circuit with that oscillator. A typical, simple, AM transmitter consists ...


7

If you're used to dealing with protocols between chips, like UART, SPI and I2C, then APRS will feel quite strange. Whereas if you've been involved with CAN, Ethernet, USB at the low level, then APRS will seem quite familiar. It's not as simple as 1200Hz means 0, and 2200Hz means 1. There are two things which make it different, firstly bit-stuffing, and ...


7

Assuming you are using coaxial cable and connectors, the case of the dummy load is contiguous with the shield of the cable and the usually-metal case of your radio. So touching the dummy load is not any more dangerous (i.e. not at all if everything is working normally) than touching your radio. The shields everywhere in the system remain at the same ...


7

Why aren't there monolithic HF ICs. There are, in the shape of actual (broadcast) AM receiver ICs, which can most likely with minimal effort be also used to transmit. However, are there technical reasons we don't see monolithic HF ICs? Your market considerations are something I'd very much agree with. Why build a monolithic IC for something that is ...


7

The GS-35A tube is the liquid cooled version of the same tube. Some hams have fabricated their own version of a liquid cooling jacket to replace the fins on the GS-35B: The designer of this jacket correctly highlights the challenges of selecting and maintaining the liquid medium since it is exposed to the full anode high voltage. Deionized water will ...


7

QRP only means low power, often 1W or less. While you could technically have a 1W SSB transceiver and call it QRP, the practical range of such a radio would be limited. It is much easier to hear a single tone over the noise than it is to hear a voice which has its energy spread over a wide range of frequencies. Thus we say CW is a more sensitive mode: it ...


7

What you describe is not far off from a common fan dipole. This is a multiband antenna consisting of several dipoles in parallel, each cut to a different length. Only instead of orienting each dipole at right angles, they are simply spread apart with spacers. The idea is that the resonant dipole for the band will have a low impedance, while the non-resonant ...


7

(See updated information further down) I found an article to address the problems all in one place in QST, September 2019. The author addresses the same problems in the question, and explains his fixes for a similar bridge-circuit-based Arduino analyzer originally published in QST, November 2017. I realize I am a newcomer and many have already figured out ...


7

I can't dig up my source for this, but I'm pretty sure these spurs are just the result of rpitx using a fractional-N PLL (that isn't in any way optimized for phase noise) to generate a square wave. You get pulses of different (discrete) widths, which means you get spurs at predictable intervals. There isn't really anything you can do to make them go away, ...


6

The metal exterior enclosure is an important component for a dummy load. The metal acts as a shield, containing any electromagnetic energy inside the can. Getting a shock is not an issue since the metal shield is at ground potential, the same as the chassis of your radio. When I had my Novice license, I used to use a lightbulb as a dummy load. It worked for ...


6

If I wanted to build a mostly-portable-but-still-comprehensive kit to use in emergencies, either my own, or simulated ones through ARES or RACES, what should I put in the kit? If you are active in ARES or RACES, they will support served agencies. The potential needs of these agencies and your role within the organization will determine the contents of your ...


6

Congratulations on your home brew project! It is great to see experimentation of this type. The two primary parameters for a capacitor are working voltage and ESR (effective series resistance), with the former being of primary interest in this case. How much power can be applied to a circuit containing a capacitor is a derivative of these parameters and of ...


6

Highest frequency stability is generally achieved when the oscillator is kept running while some following stage (or stages) is (are) keyed. However, the very high Q of a crystal-controlled oscillator permits direct keying. While the cathode, grid or plate of any stage can be keyed depending on design goals and available parts, an oscillator should be keyed ...


6

Besides not knowing about the dimensions, substrate relative permittivity $e_r$ and backside ground yes/no my guess from the picture is that the transmission line is a microstrip line and not a coplanar line. Front sides of the microstrip line printed circuit boards often also have ground metal, but that's for shielding or just practical etching reasons and ...


5

The only HT kit I've ever seen in my searches was the "TJ2B MK2 5 Band SSB Handheld Transceiver" from Youkits. From Youkits themselves: TX/RX: 5-21MHz, covering 60m, 40m, 20m,17m and 15m band (No TX on 30m) So it won't work on the 10m band, but it will work on 5 other bands. However WB8YQJ's eHam review says this: The new TJ2B "Kit B" seemed ideal, ...


5

First of all, acid-core solder is never used for electronics any more, that just isn't what it's for. I think it's still used for plumbing or other soldering where there aren't sensitive components involved. Second, aluminum solder isn't a thing. The best I can find is that there's some solder specifically for soldering aluminum to other stuff, but you ...


5

Using this site, I determined the operating range is: FM: 87.5 - 108 MHz, AM: 526.5 - 1606.5 KHz The closest ham bands are 144-148 MHz, 1800-2000 kHz. Thus, it cannot receive ham bands without modification. With modification, essentially you need to open the radio and re-tune it's frequency calibration. There is a website that documents how to do this. ...


5

The short answer is yes, they do add in parallel. But remember, the Cmin is doubled as well as the Cmax, so the tuning ratio hasn't changed. Depending on what you are using them for, this may or may not matter. Of course you can offset this with an inductor.


5

While 1200 baud packet radio uses AFSK with 1200 and 2200 tones, they don't correspond with digital 1's and 0's directly. It employs NRZI encoding as well as bit stuffing. Non-return to zero inverted (NRZI) means that a 0 is encoded as a change in tone, and a 1 is encoded as no change in tone. This depends on having an accurate clock on both ends. But even ...


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