Idea Box: More Simple HF CW Transceiver(s).

 Here is another one for the idea box.

While I am doing stuff for much higher frequencies I am still thinking of this in connection with my "one QSO per band with home made gear" challenge. I was thinking of using a kit (or two) for a simple HF CW transceiver using a direct conversion receiver.

Some examples of those kits are the Pixie, the Rockmite, the Frog Sound and the 49'er. I have a box with some of those kits, and some of them should be quite easy to convert to HF bands up to 18MHz without too much loss of performance.

For higher frequencies I suspect that the receiver sensitivity will be insufficient for efficient work on those bands (21/24/28MHz). Here it is probably a good idea to use two kits, one for TX and one for RX, adding a preamplifier for improved RX sensitivity, and possibly a PA for higher TX power.

Each transceiver would be modified to use a SI5351 synthesizer board. This board should be controller (programmed) by, e.g. an Arduino, so I will have to learn another skill: Micro-controller programming. There are libraries and some programs in existence, but the programming skill will come in handy if I want to extend functions.

A simple 28MHz model could possibly be used as base transceiver for transverters to higher bands. This would not need RX modifications and could possibly be using just a simple TRX kit. I am well aware of the lack of CW activity, especially on the VHF/UHF/SHF bands, but a single QSO, or a few, should be possible.

I do have two other kits for CW transceivers, the QRP Labs' QCX+, with components for 20m and 60m. Still need to be built, but that is a matter of finding time to add those.

Do I have too many kits and projects? Yes, but I will not have any time to be bored, that is certain ...

Another one of the ideas stacking up ;)

My "Home Made" Challenge.

I have been thinking of challenging myself with respect to (partly, at least) home made transmit and receive equipment used for making minimum one contact or received signal on as many bands, and in as many modes, as I can possibly do.

First my definition on "home made". it can  be a few different things, all involving some thinking or building activity, for example:

- use of equipment not designed for amateur radio, e.g. using a satellite TV LNB for receiving 10GHz amateur radio signals.

- use of modified (possibly surplus) equipment, e.g. using a HB-100 Doppler radar module for transmitting wideband FM or ATV on 10GHz, a home made (or modified) modulator is needed.

- using a kit I built/assembled (maybe modified) myself, e.g. the very simple Pixie transceiver kit.

- building transmitter and/or receiver circuits in non-kit form.

All of this can be arranged in stages, for example:

- building a transmitter and using an available receiver (kit or no kit).

- building a receiver (in addition) (kit or no kit).

- full transceiver (modified, built, kit or no kit).

Right now the status for the "home made" challenge is as follows, for the OZ9QV callsign:

80m: CW TRX, the single frequency - band modified - Pixie kit. - one QSO

60m: CW TRX, the single frequency - band modified - Pixie kit. - one QSO

40m: CW TRX, the single frequency -      unmodified - Pixie kit. - one QSO

This is a long term challenge that I intend to work on, slowly increasing the scope of bands, modes etc. Modes should include CW, Phone (DSB/SSB/AM/FM - DIGI-voice?), Digital modes (e.g. FT8).

Simple monitoring RXs should be included in the challenge, too.

This will involve using many kinds of home made equipment, all the way from simple CW TX,RX to SSB TX,RX.

More than enough projects to keep me busy!

Another part of the challenge is attempting to work 100 contacts, QRO or QRP with home made TX&RX, then 100 DXCC entities, just on a single band.

Challenges not including home made stuff could be 100 contacts or 100 DXCCs with QRP on as many bands as possible.

I could probably dream up other challenges, but let us see what I manage to get done. 

Receiving FT8 With a Pixie.

After a long wait I received some crystals for the FT8, JS8Call and WSPR/QRSS frequencies on 40m and 20m, ordered some time in March.

The Ebay seller was not at fault, I suspect that the COVID-19 situation had left the package stranded somewhere on the way, for a long while. Other packages from the USA have not arrived yet, either, but who knows, they may appear one sunny day.

One set of crystals has 3 crystals per band:

7074kHz (FT8)

7078kHz (JS8Call)

7038.6kHz (WSPR/QRSS)

14074kHz (FT8)

14078kHz (JS8Call)

14095.6kHz (WSPR/QRSS)

In previous posts I have written about some experiments with the Pixie kits, and now is the opportunity to continue with that

The original 7023kHz crystal was unsoldered and a 7074kHz crystal soldered in. I am leaving the long leads at the crystal, as I think I will use it for a different receiver (or, maybe a transceiver). The frequency was adjusted to 7074.00kHz, so the test could begin. During the day not too many signals were heard, but in the evening the signals are coming in very nicely.

The antenna is a low hanging 10-15-20-40-80m dipole, so not the best, but this is excellent for the test.

Connecting the Pixie to the antenna and a set of computer speakers, FT8 signals were heard, immediately.

A quick test with a laptop, using its microphone, yielded immediate FT8 spots. A USB sound interface was found and connected in place of the speaker/microphone, and the spots poured down the screen. In the span of less than 2 hours spots were seen from North and South America, Europe, Africa and Asia. 

The system is actually working.

I left the system running over night, and in the morning I could add Oceania to the list (Indonesia). No Australia or New Zealand, but that was to be expected at this time of the year.

The experiment is a success, so now I consider the next step:

- setting the same receiver up with a raspberry Pi running headless, but using VNC, or

- inserting the 7038.6kHz crystal and setting up with a Raspberry Pi for QRSS, and maybe also WSPR.

If I just set the Pixie up for QRSS with an older Raspberry Pi, this could make for a low power, solar powered QRSS grabber system, so that is a tempting option.

Further steps could be a low power DSB or phasing SSB transceiver for FT8 or JS8Call, at first for 40m, later for 20m.

Now, if I could find a corresponding set of crystals for 60m or 80m, that could be interesting, too. On 80m, however, I could possibly use a ceramic resonator and tune it to the FT8 frequency (3573kHz). For the JS8Call a standard NTSC colour crystal (3579kHz) could be used, re-tuned to 3578kHz. It *may* be possible to use a Super-VXO (2 or more crystals in parallel) type oscillator for generating the 3573kHz signal.  

As always, too many ideas, but it is never boring.

Ha ! My Pixie Test Mistake. You May Laugh ;)

OOPS!

Looking at my radio desk I found out that I had not connected the 80m Pixie modified for transmission only, to the SWR-meter and the antenna. There was another BNC-BNC cable on the radio desk.

The stability and frequency offset was still not good, but the output was there. Also, the erratic behaviour of the frequency when keying the TX was gone. It was most likely due to RF floating all around.

The 472kHz version is still not good. No oscillation I can detect. Some experimentation with the oscillator circuit will probably provide oscillation, and some RF output from that version of the Pixie.

Laughing is allowed, I did chuckle when I saw the mistake.

Now I need to see if I can make a receiver version with sufficient stability. Otherwise I will have to go for some "real home brew".

Quick Pixie Updates: Ceramic Resonators for TX.

After some more experiments with the Pixie kits I am suspending the Pixie for a while.

Versions of the Pixie modified for transmit only, 80m version and 630m version with modified inductors and capacitors in the frequency dependent circuits, and the components specific to the receive mode have been omitted. For example, the diode and switch for RX oscillator offset has been removed. Further, a variable capacitor ("Polyvaricon") has been connected from the crystal to ground, in place of the diode offset "capacitor")

80m:
The oscillator does oscillate in the "RX mode", and the frequency range is about 3500 - 3600kHz. When keying, however the oscillator frequency still changes frequency, sometimes in an unpredictable way (sometimes up, sometimes down).
I suspect 2 reasons:
- the oscillator voltage is not stabilised
- the load of the oscillator changes when switching to "TX" mode.
Further, the output of the transmitter with the ceramic resonator in the circuit is too low to register on the SWR/PWR meter. Not exactly a resounding success. This could be due to a lower Q of the ceramic resonators, resulting in a lower oscillator output.

630m:
I could not register any output from the oscillator. There can be several reasons:
- the oscillator may be more loaded by the buffer stage
- the capacitive load of the oscillator capacitors may be too high
- the frequency determining capacitors may have a low Q
- the Q of the ceramic resonator may be too low for solid oscillator loop gain
- the capacitor ratio in the feedback loop may result in a loop gain below 1.

My conclusion is that the basic design of the Pixie is too simple for a wide range (ceramic resonator controlled) transmitter, though it may be brought to work OK with a crystal, with some VXO functionality. A few switched crystals may provide some coverage, especially in the 40m band. I have crystals resonating on 7000, 7015, 7023, 7030 and 7040kHz, possibly 7035kHz. From box73,de 7005, 7010, 7020, 7035, 7050, 7052, 7055 and 7070 are available This should provide some coverage of the 40m CW band, so I might try that and see how much of the band can be covered with such a setup.
I see that several Xtal frequencies for the 10MHz band are available at box73.de , so a 10MHz version of the switched Xtal TX may be feasible. Frequencies available from there:
10105, 10106, 10115, 10116, 10120, 10135 and 10145kHz. This should provide good coverage of the 10MHz band with a VXO circuit.
Also from Box73.de :
80m : 3530, 3540, 3550, 3555, 3560 and 3570kHz. Generally available is also 3579kHz Partial coverage of 80m looks possible.
160m: 1800 and 1820 available from box73.de. Generally available: 1843kHz. I do have a crystal for 1963kHz.

Experiments with crystal control of the Pixie should therefore be available to me on the following bands:
- 160m
- 80m
- 40m
- 30m

While I do have crystals for higher bands (14,18,21,24 and 28MHz) I consider that the Pixie is probably not suitable for those bands. I could do a test on 28MHz, just to see what the kit does, but I do not expect good results. It may possibly work with better transistors, and with lower power.

I am still looking for crystals in the 5250 - 5450 kHz band.

Receiver experiments, with the offset diode circuit removed, should prove interesting enough. For a receiver a stabilised voltage supply can easily be arranged

Other experiments have been suggested by VK3YE on his page :
The Pixie Hack Challenge

I may try out a few of those at a later stage.

As you can see, there are still many experiments/hacks possible with the Pixie kits. That is why I purchased quite a few before starting the experimentation.

I may have a pause in the Pixie play now. Many other projects I want to do. We shall see.

Pixie tests with VXO and Ceramic Resonators.

Quick test today using ceramic resonators.
40m model:
Even with a 5 - 60pF variable capacitor the frequency could be pulled down to under 7.000MHz, with a ceramic resonator for 7160kHz. The stability, however, was not sufficient with the Pixie. The tuning was fiddly, and the TX signal had a significant chirp, and the receive frequency was drifting too much for my taste. Well, it was clearly audible ...
Further, the RX offset of the oscillator, when using a crystal in series with the variable capacitor, was insufficient at the lowest frequency, even when it was set to maximum, i.e. the RX local oscillator (BFO) was too close to zero beat.
The 80m version did not fare much better. Yes, it was a bit better, but still had chirp on the TX and some drifting on the RX the RX could not be pulled down to the band edge, either, but did have a sufficient range to have been useful.

More experiments with an inductor added to the VXO (crystal) should be an interesting experiment. It might provide for a better stability, and somewhat better offset. This needs to be tested.

It may be possible to use one Pixie as RX and another as TX, providing a "spot" function, but I doubt the stability will be sufficient with the ceramic resonators.

Because VK3YE has tested oscillators and even regenerative receivers with ceramic resonators, and achieved sufficient stability for CW operation, I would consider the Pixie as too simple for good results as a frequency agile CW transceiver. It would be quite suitable for simple fixed frequency operation, e.g. as a monitor receiver for FT8. Crystals for such a receiver (20m and 40m) should arrive in about a week, if not delayed by the corona virus situation. A test of the Pixie as a simple QRSS RX should be another simple experiment.

Idea Box: QRSS With Simple Home Made Equipment.

Some years ago, while living in the Netherlands, I made a few experiments in receiving QRSS (very slow morse) with a receiver and a computer running the SpectrumLab software under Wine in Linux.

Despite living in an apartment I had some success, but when I moved everything was dismantled.

I have still been following the developments in the QRSS activity, and I should like to get going again. Running a so-called Grabber (QRSS receiver does not take too much time out for other activities, because the spectrograms are simply up-loaded to a website for all to see.
QRSS provides a quite good weak signal performance, so it is usable for propagation monitoring, provided that there are some QRSS transmitters active.

Last time I was running a QRSS Grabber was before the time of the low cost Raspberry Pi single board computer, but these days it is an excellent candidate for running grabber software.

Now, what about receivers ? I was thinking of running a very simple, low cost receiver to begin with, e.g. a modifies Pixie kit.
The Pixie is an extremely simple 40m single frequency CW transceiver, mostly supplied with a 7023kHz crystal. On 40m it just might be capable of running a grabber on 7040kHz. The "IF" will be 17kHz, that should be within the capabilities of spectrum analysis programs for the Raspberry Pi. Alternatively, a different crystal, say 7030, 7035 or even 7038kHz crystal could be used, substantially bringing the "IF" down. If the missing image selectivity becomes a problem, a simple, single crystal filter with a 7040kHz crystal filter could be used.

To be fair, the Pixie is very low cost, a kit can be had for less than $5, so it is an excellent candidate for experiments. The design, however, is probably quite reliable, but certainly not high performance.

In the coming year I hope to have room for some experiments with QRSS, but a higher priority is getting a signal through the QO100 satellite.