Hot answers tagged

9

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 ...


8

My understanding of "QRP" is simply the use of as little power as possible to make contacts over interesting distances. There isn't a specific power level that equates to "QRP" - it is more a function of what's less than expected. 1W on 2m/UHF for 10 mile simplex (or local/regional repeater communications) isn't QRP. 0.1W on 2m/UHF for 250 mile simplex ...


8

My personal opinion is that QRP means using significantly less power than is customary for a given mode of operation. In that sense, a 5W HT would not be QRP because pretty much everybody else with an HT is also operating at (or near) 5W. 0.5W might be considered QRP in this case.


7

If you look up "link dipole" or "linked dipole" you will find several designs that do just that. It works well for QRP or even for 100W. The ones I've seen have used several different connectors: alligator clips, quick disconnect spade terminals, Anderson PowerPoles, and banana plugs, to name a few. Of those, alligator clips are probably ...


6

20 meters. This assumes you're wanting to work back to the States or into Europe. If your primary interest is local in South America, then I'd go with 40 meters. An advantage is the ease of dealing with a smaller antenna. While not a single-band radio, I'd seriously consider one of the KD1JV rigs. Occasionally available as kits, but now commercially ...


5

The output impedance isn't especially important: in fact I believe it uses a nonlinear amplifier so the concept doesn't really apply. What does matter is the intended load impedance, which for any amateur radio application you can assume to be 50 ohms unless otherwise specified. To verify, I modelled the low-pass filter part of the circuit from the manual: ...


5

Doppler spreading is the change in received frequency from a distance transmitter due to the rise and fall of the ionosphere along the signal path. When the effective height of the ionosphere rises, this lengthens the path and causes the received frequency to drop; when it falls the path decreases and the frequency rises. You can measure this frequency ...


5

A QRP transceiver is just a transceiver that operates on low power (usually less than 5 watts). If you look at the international Q Code, you will see that QRP simply means 'low power', and QRO means 'high power'. However, what you are talking about is a QRP transceiver kit. Such kits are usually by necessity a fairly simple design, and the simplest ...


5

Without getting into specific product recommendations, I believe the simplest way is as follows: Obtain a license. An amateur license is required for using amateur bands. I am not aware of any non-amateur bands using FT8. A technician-level license is sufficient in USA for VHF and UHF but it looks like a General level license is needed for the HF bands. ...


5

Generally, making an antenna shorter makes it less efficient. This means some fraction of your transmitter's power is used to make the antenna and/or surrounding soil warmer instead of radiating where someone might receive it. The fraction of power lost is the same whether the transmit power is 3W or 300W. So the detrimental effects of a loading coil are not ...


4

Q1 forms a Colpitts crystal oscillator. It uses the reverse biased D2 as a varicap (variable capacitor) to pull the crystal frequency by 700 to 800 Hz, This frequency beats with the received frequency to produce the audible CW tone. The adjustability of the pull through W1 also allows a simple, limited range RIT function during receive.


4

CW is preferred over SSB for low power (QRP) operation because CW delivers better signal-to-noise ratio (S/N or SNR) than SSB. Because a CW signal occupies about an order of magnitude less bandwidth than an SSB signal, a narrower receiving filter can be used, which admits all of the signal and a much smaller amount of noise energy than a wider SSB filter. ...


4

I see what your problem is. That's a 1.4 meter long, based-loaded, telescoping, end-fed vertical antenna. It has significant losses on 40 meters. Furthermore, all end-fed antennas require a good RF return, such as a resonant elevated radial or counterpoise. Since you don't mention that, that indicates to me that very little of your signal is actually ...


4

It makes a difference of: $$ 10 \times \log_{10}\left(3 \over 5\right) = 2.2 \:\mathrm{dB} $$ How big is 2.2 dB? See How big is a decibel? It's also relevant to note: if the 12V battery is lead acid, the charged voltage can be as high as 13.7. Furthermore, while a boost converter might further increase your transmit power, it's likely to make noise which ...


3

Although it's highly opinionated, it may be defined as operating at 5% or less than standard 'barefoot' operating power on your band, by convention. So, for most HF, 100W is the standard power, 5W is considered QRP. For VHF, most handhelds (which are the most frequently used on that band) operate at 5W, so QRP would be 250mW. Of course, that doesn't ...


3

If a transmitter is moving toward or away from you, the received frequency will get shifted up or down, depending on direction and rate of movement. Even if the transmitter and receiver are not moving relative to each other, but a reflector, reflecting the signal between them, is moving, the you can get the same Doppler effect. It's well known (at minimum, ...


3

When you ask if a QRP transmitter could be used to solve your problem, I presume that you mean a low-powered transmitter on HF, meaning roughly 3 – 30 MHz. That would solve the problem of limited range associated with the VHF and higher-frequency bands, but a large antenna would be necessary. The problem is that radio spectrum, especially in the HF ...


3

As the saying goes, if you build a better mousetrap, then the world will beat a path to your door; but in the modern era, you do need to get the word out first somehow. A website with complete information about your awesome kit is essential. That way, interested hams can find your site either directly from a URL, or from a search engine. Don't neglect the ...


3

If you haven't done much QRP operating, QRP is a funny thing. Sometimes propagation is great, and you wonder why anyone would bother with 100 W or more. I'll never forget my first DX QSO, from Oregon to Estonia, running 11 W to a vertical, by gray-line propagation at the bottom of the sunspot cycle in 2006. Other times it seems like a complete waste of ...


3

I haven't experimented myself, but the USB-to-12VDC adapters surely use a boost converter, and those make RF noise. I have no idea what frequencies they make noise on (tens or hundreds of kilohertz?), but I wouldn't be surprised if noise (harmonics of the original frequencies most likely) makes it up to the ham bands. Such noise may or may not be a deal-...


2

Clandestine can be very effective. A thin wire hanging out of your window is hard to see, especially if you only have it outside while operating. Commercially built tuners aren't expensive either. Another option to consider is MCW (modulated CW) where you send the Morse tones over audio via VHF/UHF FM. If you have enough CW fans there you may be able ...


2

There's at least one video on YouTube concerning a Pixie (normally a 40m QRP CW-only transceiver, with rather questionable control of harmonics) converted to use the output audio amplifier IC as a modulator for AM transmission. Another Pixie could be used as a receiver, as long as they have the same frequency crystal. This is about as simple and cheap as ...


2

It happens slowly and organically. Yes, most of these folks have probably mentioned on bulletin boards, forums, or mailing lists that they have a new project they're working on. They aren't running around putting those notes in all the lists though. They're putting it on lists in which they're active members and in ways they think that community might like, ...


2

If you read contest rules, the QRP section is for those using 5W or less (sometimes 10W or less) no matter what type of transmitter you use. So you can enter the FM QRP section of a VHF or UHF contest when using a handheld on full (5w) power.


2

ITU Recommendation F.1487-0 defines methods for testing HF ionospheric paths for bandwidths up to 12 kHz. While ionospheric propagation can be complex, this document provides a starting point for the widely applicable basics. It characterizes an HF channel with two parameters: multipath differential time delay, and Doppler spread. The multipath ...


2

Your 10W output from the power bank will not be 10W after the upconverter has changed the voltage -- if you're lucky, it'll be seven or eight watts, but it might be as little as four. The first one you lined is rated for a real 0.8 A output, but I'm certain it will need more than 2 A from your power bank. Because of that, while you could (inefficiently) use ...


2

Look for a USB-PD power bank rated 27W or higher (which should guarantee it supports 15V output), and a 12V and/or 15V trigger (a small device or cable with a USB connector on one side, a chip that does the PD negotiation, and DC output on the other, often on a 5.5x2.1 mm barrel connector). That way you will have the power bank regulating up the battery ...


2

Check to see if your BNC to banana plug adapter has caps that unscrew to allow wires without banana plugs to be connected. Or get a BNC to screw terminal adapter. Or ger a short piece of coax with a BNC connctor and run the other end into a small box to screws coming out the sides of the box to attach the antenna wires. Then you could put a small eye bolt in ...


1

Any transmissive data channel will hit a lower power limit for readability when the signal no longer exceeds the noise floor of the transmission mode. This is another way of saying that the minimum-required signal strength for establishing data exchange is dependent on the position of the noise floor. So understanding the physics and math behind S/N ratios ...


Only top voted, non community-wiki answers of a minimum length are eligible