FST4W - Quick overview of the main differences between RFZero and QDX (QRPLabs) and the Rx only KiWiSDR #fst4
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Alan G4ZFQ
On 03/02/2023 10:21, Erwin - PE3ES - F4VTQ via groups.io wrote:
he now offers 2 QDX variants, one for the low bands, the other for the high bands.Erwin The QDX is limited in several ways. There are only 3 LPF positions. So 2 versions that are pre-configured for the lower HF and higher HF are marketed. However a user may configure a QDX in any way he wishes but the other limitation is that the diode LPF switching begins to get lossy below 80m. Note the third version QDX-M, a "barebones" version. This has no band switching, intended as a mono band transceiver for LF. But it is configurable for any band from 2200m to 10m. An enthusiastic modifier could use this with relay driven switching but so far that seems unlikely to be marketed. Another interesting product soon coming from QRP Labs is the Progrock2, may be disciplined by GPS. It seems to have the potential to have the accuracy of a Kiwi but we will have to wait to see how close it gets. 73 Alan G4ZFQ |
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Erwin - PE3ES - F4VTQ
I have indeed just seen at Hans' site that he now offers 2 QDX variants, one for the low bands, the other for the high bands.
If that is going to be one QDX for all HF bands in the future ?? Erwin |
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Alan G4ZFQ
On 01/02/2023 14:52, Glenn Elmore wrote:
The disciplined frequency reference <http://sonic.net/~n6gn/OSHW/Reference.html> Alan, if you could make use of one of these, I'd be happy to send you one.Glenn, Many thanks for the offer. I am interested but I do not think I'd be able to provide regular transmissions without a major reorganisation here. There must be a better candidate. 73 Alan |
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Paul WB6CXC (tech-blog: wb6cxc.com)
On Wed, Feb 1, 2023 at 01:05 PM, Rob Robinett wrote:
But the QDX audio freqeuncy measurement technique can only detect one audio tone at a time. So it is limited in the same way as the RFZero.Sorry, I misunderstood "at the same time", thinking it meant something like sequential mode switching . Yes, the QDX and RFzero can only generate a single FSK signal. Even if the QDX could measure multiple combined audio inputs, the synthesizer and amplifier sections couldn't work with that information. A different design using the same Si5351 clock-generator chip could generate three truly simultaneous FSK signals, but a linear amplifier or power-combiner would be needed -- there are probably better ways to accomplish the same thing. |
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Rob Robinett
The RFZero includes band scanning configuration options, but it needs a power amp and switchable low pass filters to be a 5W multiband solution. Bo has a complete discussion of how to do that on his site at: https://rfzero.net/examples/fst4w-transmitter/ But you will have to build the power amp and construct the switchable LPF. The RFZ includes 7 SW controllable output pins for LPF control and/or antenna switching, so it is a great maker's sandbox. On Wed, Feb 1, 2023 at 1:38 PM KD2OM <steve@...> wrote:
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I am thinking of adding a relay controlled by one RFZero to switch between two RFZeros for either two modes with the same amplifier or two bands with two amplifiers.
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73 Steve KD2OM . On Feb 1, 2023, at 16:05, Rob Robinett <rob@...> wrote:
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Rob Robinett
But the QDX audio freqeuncy measurement technique can only detect one audio tone at a time. So it is limited in the same way as the RFZero. On Wed, Feb 1, 2023 at 09:50 AM, Bryan Klofas wrote: --
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Paul WB6CXC (tech-blog: wb6cxc.com)
On Wed, Feb 1, 2023 at 09:50 AM, Bryan Klofas wrote:
It seems that since the QDX requires WSJT-X, that's a no go. But maybe the audio stream sent to the QDX can be hacked/modified?The QDX will accept USB-audio and CAT commands from any source. When I was testing QDX stability I put together a simple C# (Windows) program that sent CAT (for frequency setting and TX/RX control) and audio to the QDX and it worked just fine. There's no reason that someone couldn't write a program to do what you want. |
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Hi
I can only speak for the RFzero. The H/W cannot generate four signals at the same time, only two with relaxed RF performance. But if you want to use the same PA for both/all four frequencies it may have to run in Class A, or close to, in order to keep the IMD under control. Even for 5 W ham beacons to run in Class A requires a good portion of long lasting financial commitment. I forgot to mention, that the KH6HME/B 2 m beacon uses an RFzero, and in June it has been on the air for three years. Bo www.rudius.net/oz2m :: www.rfzero.net |
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Bryan Klofas
Hey Erwin--
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Do either of the transmitters allow for multiple FST4W mode TX at the same time? For example, at the top of the hour, start a -120, -300, -900, and -1800 transmission at the same time, with slightly different frequencies. Just keep repeating the shorter time modes until the -1800 ends, then start it all over again. This might be cool to see differences in SNR at the receiving site over the same path. It seems that since the QDX requires WSJT-X, that's a no go. But maybe the audio stream sent to the QDX can be hacked/modified? I'm not sure about the RFZero. Thanks, have a great day! -- Bryan Klofas KF6ZEO On 2/1/23 02:33, Erwin - PE3ES - F4VTQ via groups.io wrote:
To get on the air with FST4W many options exist, the below gives some insight in the differences between RFZero and QDX. Both are smart choices to get on the air quickly and enjoy the benefits of transmitting FST4W. |
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Hi
Re the RFzero are a few additional comments can work on any band till 300 MHz (and above with mods) Bo> the modification needed is changing one function from calculateTones() to calculateTonesMulti() for a multiplied use. For transverter use nothing has to be changed. Out of the box the RFzero can generate WSPR on 23 cm has no PA and delivers 13 dBm (20 mW) output 400 kHz to 200 MHz Bo> more than 13 dbm and typically between 14 dBm and 15 dBm can only run one program at a time (so not a GPSDO in parallel to transmitting FST4W) Bo> deliberately by design to make it easier for others to study and modify. If needed there are multitasking OSes available for the SAMD21 Bo> all frequencies generated are locked to GPS. You could say that the RFzero is a frequency changing GPSDO. A GPSDO does not necessarily 10 MHz. The sequence timing is also GPS locked Bo> the RFzero comes 99% assembled. Only LEDs and headers need to be mounted if required Bo> all that is needed to generate 5 W is a suitable PA and a LPF bank Bo www.rudius.net/oz2m :: www.rfzero.net |
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Rob Robinett
Arne has creased a Grafana page at his wspr.live site which shows a significant increase in the number of FST4W transmit sites over the last 2 weeks:  Scroll down on his page to see maps of the FST4W tx and rx sites around the world:  Glenn's GPSDO board, a QDX and a Pi makes a very low cost FST4W tx station and I hope that we will soon see many more, especially from Asia, South America and Africa. On Wed, Feb 1, 2023 at 6:52 AM Glenn Elmore <n6gn@...> wrote:
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Glenn Elmore
Alan and others, It would seem that the only thing in the way of a QDX monobander going to frequencies above 10m is a LPF and programming. Whether or not QRP Labs will see the value in extending it is a good question but from my experience with 2m and shorter wavelength WSPR, I think there may be a wealth of opportunity up there. It's very clear that spots >900 km distant are routinely possible on every VHF through microwave amateur band from only a modest station using WSPR and aircraft scatter. Given hardware, I'd expect FST4W to work as well or better. There are currently 2m and 70cm beacons on the island of Hawaii that are frequently spotted on the mainland 4100 km distant. Examination of those .wav files and their low spectral spreading, most of the time, leads me to think that FST4W would be an even better tool. There are presently only a very few FST4W HF (>3 MHz) stations
transmitting but the limited data we already have gained is
proving a watershed for understanding propagation modes in ways
that haven't been available before. More to come on this in a
paper soon (hopefully) to be presented at HamSci.
To increase the number of spots I'm very hopeful that the QDX
might play a central role. Towards that end, The disciplined
frequency reference I've created, still rather alpha, can be
made available for any who might like to help. I've already sent
out a few of those which will hopefully be paired with more QDX's
and increase the number of available signals to spot. Quite a few
of us on this list are already helping by scheduling wsprdaemon to
spot FST4W as well as WSPR and the results have been very
promising. I'm almost out of the initial 'supply' of these
references but am considering another order to test minor
hardware and software changes and increase to increase
availability. Alan, if you could make use of one of these, I'd
be happy to send you one. Glenn n6gn Fort Collins,CO
On 2/1/23 03:49, Alan G4ZFQ wrote:
On 01/02/2023 10:33, Erwin - PE3ES - F4VTQ via groups.io wrote: |
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Erwin, I have been using the RFZero for transmitting FST4W for quite some time. It works so well I bought another one. I am using a 5 watt amplifier from G0MRF for transmitting on 630 meters. I also have a 300 watt amplifier for the same band. I am thinking of setting the second RFZero to transmit WSPR on the same band alternating times with the other RFZero. I use the KiwiSDRs for receive along with an HF Discovery and RSP2dx. 73 Steve KD2OM On 2/1/23 10:33, Erwin - PE3ES - F4VTQ
via groups.io wrote:
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Alan G4ZFQ
On 01/02/2023 10:33, Erwin - PE3ES - F4VTQ via groups.io wrote:
QDX can only work 20-80 meter bandsErwin, I'm not sure of the exact situation but the QDX should soon be working on all HF bands. Right now definitely 80m to 10m. Below that I'm not sure but it is being implemented. Yes, a stable reference around 25MHz is required. I'm looking into resurrecting my old 10KHz Rockwell GPS/PLL. Maybe one day but I get distracted:-) Some are using it with small computers like the Raspberry Pi. 73 Alan G4ZFQ |
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Erwin - PE3ES - F4VTQ
To get on the air with FST4W many options exist, the below gives some insight in the differences between RFZero and QDX. Both are smart choices to get on the air quickly and enjoy the benefits of transmitting FST4W.
RFZero can work on any band till 300 MHz (and above with mods)
onboard GPS stabilized frequency control; RFZero can be used as GPSDO
has no PA and delivers 13 dBm (20 mW) output 400 kHz to 200 MHz
is very flexible as all programs can be switched and changed
can only run one program at a time (so not a GPSDO in parallel to transmitting FST4W)
a QRPlabs 5W PA would be a good addition for higher power FST4W transmissions
completely stand-alone
QDX
can only work 20-80 meter bands
needs a mod and an external reference frequency to get stable enough to transmit FST4W on Rx or Tx
has about 5W output on 20-30-40-80 meter band
only does digital modes
needs WSJTx on a separate computer to do FST4W
KiWiSDR
can only receive
onboard GPS makes it stable enough for FST4W decoding
Prices for RFZero and QDX are about the same US$ / EUR 80
Comments are appreciated Erwin / PE3ES - F4VTQ |
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