2020-02-25

Second Crystal/Ceramic Resonator Tester

I built a second crystal tester today. This time I used 470pF capacitors for the Colpitts oscillator "resonating capacitance", and a larger transfer capacitor.
As expected, this worked nicely with ceramic resonators (but not 3-pin filters) down to the lowest available, 400kHz, and up to about 2MHz (crystals). One 1843kHz crystal did not work, but a 1963kHz crystal did. Maybe the 1843 crystal was poor quality.

I expect that I should build the third one of of the crystal testers, this time with 100pF "resonating capacitance". This **should** provide tests the intermediate frequency range of 1.8 - 8MHz, at least for crystals and ceramic resonators.

All in all I am happy with the results, I was warned that the crystal tester kit, advertised as 1 - 50MHz crystal tester, was not working in the full range, so I had a few kits taken home.

I could see that one of the ceramic resonators (marked 480kHz) oscillated on 476kHz, i.e. inside the 630m band. I suspect that I can build a VXO with one of those resonators, covering the full 472 - 479kHz band. Oops ! Yet another possible project to try out. Maybe a modified Pixie kit can be brought to work on 472kHz - I would not be surprised.

2020-02-24

Test Equipment: Crystal Tester Kit.

I just assembled a low cost Chinese kit claiming to test crystals from 1 - 50MHz, with a counter w/5-digit display). Assembly time, taking things easy, was about 1 hour.

I already suspected that the kit would not work down to 1MHz, for this reason: The crystal oscillator is a Colpitts oscillator with the capacitances across the crystal (B-E and E-GND) being only 22pF each. The capacitances in the Pixie kit's oscillators is much higher, and that was designed for 7MHz.
This was confirmed when testing crystals. Below 5MHz hardly any crystals would generate a countable signal. However, crystals up to 28MHz would generate countable signals.
I suspect that a different tester with, say 100pF capacitors would likely work down to about 2MHz, and 470pF capacitors down to about 400kHz.
I do have another kit or two, so I will probably build those with the above mentioned modifications.
One more test was done: Trying out ceramic resonators. Resonators (2-pin) or filters (3-pin) were tested. None worked on less than 10MHz in this circuit, but did work up to 20MHz, with rather consistent results for the resonators (2-pin), and inconsistently with some of the filters (3-pin). I suspect the low capacitance values are the reason for this.
Also, a more suitable oscillator type for the filters should be tested.
I may end up with a counter with an 8-digit display and some dedicated oscillators as my crystal tester. This could be interesting for testing frequencies for crystals to be used in crystal filters. It is likely that a set of modified Pixie oscillators would do the job.

Finishing one project creating more possible projects. Why am I not surprised.
I do have a few Pixie kits lying around, so maybe the next project should be an unmodified Pixie transceiver, with the exception of using an external crystal or ceramic resonator for the oscillator.

2020-01-25

Idea Box: Simple Transmitter Circuits w/Ceramic Resonators.

Over the latest year or two I have collected some ceramic filters/resonators for different frequencies.

A simple oscillator (VXO) controlled by a ceramic resonator, either directly on the TX frequency or using a doubler or divider can generate signals in several amateur bands, and here are some ideas for the frequency generation:

Idea Box:
Simple TX for CW (maybe later DSB) for MF and HF bands with ceramic resonators:
- 472kHz: VXO w/480kHz ceramic resonator (472-479 ?) (CW)
- 1.8MHz: VXO w/3686kHz ceramic resonator and divide-by-2 (1800-1840?) (CW)
- 3.5MHz: VXO w/3580kHz ceramic resonator (3500-3575?) (CW)
- 3.6MHz: VXO w/3686kHz ceramic resonator (3600-3680?) (DSB)
- 5.2MHz: VXO w/5500kHz ceramic resonator (5350-5450?) (CW/DSB)
- 7.0MHz: VXO w/7160kHz ceramic resonator (7000?-7150?) (CW/DSB)
- 7.0MHz: VXO w/3580kHz CR and doubler (7000 - 7150?) (CW)(DSB?)
- 10MHz: Super-VXO with 5068kHz crystals
All with PA modules (per band), and a signal derived from the exciter, to a single LCD frequency counter, and, of course CW keying circuit/DSB modulator.
All this could be expanded to a simple TRX with direct conversion RX. RIT control will be needed, especially for the CW mode.

Using a PCB from the Pixie kit could provide some basis for the simple TX circuits, with suitable modifications, e.g. using a ceramic resonator in place of the original crystal, and a simple modification of the low pass filter. This idea comes from VK3YE who made the "Pixie Hack Challenge", providing ideas for different uses of this very low cost kit, with a few additional components, and sometimes removing some components. I think he came up with 12 ideas fo Pixie Hacks, but I do not think he had the transmitter mod. He did, indeed have a hack, using the Pixie as a direct conversion receiver, tuned with a ceramic resonator, but I do not see why that should not work with a TX hack as well.

2020-01-24

Quick Test of Test Equipment Modules.


I have collected some test equipment stuff over the last several months.
I finally got to test some of it, and there is more to test. This was a quick test of the following test equipment (boards or in a casing):

- Signal generator, 500kHz - 470MHz, spec output: -70dBm - -125dBm. Signal could be heard on the frequency tested, so it appears to be in good working order.

- DDS function generator:
This was supposed to deliver a signal on a max frequency of 8MHz. Well, it does, but not variable up to 8MHz. Just 1MHz, 2MHz, 4MHz and 8MHz. Useless on amateur bands.
The function generator can deliver sine, sawtooth and square waves. Spec says from 1 - 65500Hz. I can only set the frequency with 100Hz steps at the moment. There may be another trick that I have not yet learned, to step with 10 or 1Hz.
This one was a disappointment. The function generator should be somewhat useful, though.

- Frequency counter modules some with possibility for IF frequency offset.
some LCD modules could be adjusted to show 432MHz nicely with 1-200Hz tolerance.
Similarly some LED (8 digit) modules could be adjusted to the same frequency tolerance.
One LED module was dead. No 5V output voltage from the regulator. I expect it can be fixed
One LED module had missing segments. A short at the PCB was the reason, and it works fine now.
One 500MHz module could not be adjusted to the wanted tolerance, the reference frequency offset was about 19ppm (too low). I expect that a different trimmer capacitor will make it possible to adjust correctly. Maybe a different crystal, I think I have some lying around.
All of the above (functional) counter modules were subjected to a quick test/adjustment with a 432MHz signal from a hand held TRX
A last (6 digit) counter module could not detect/count the 432MHz signal, must be tested with a lower frequency.
Finally, a larger counter module, supposed to count to 2.4GHz, was tested with the 432MHz signal, and had quite an offset. The reference frequency did not appear to be adjustable, it is a canned crystal oscillator. More investigation necessary. It may be that an external reference generator (GPSDO ?) is a good idea for this module.

- LCR meters:
Two LC-100 modules were tested. They seem to have survived getting connected to a 9V supply, when only 5V was "expected". (Display characters went rather dark)
Getting a correct 5V changed the display, so it became readable, and the modules appear to work correctly.

- 35 - 4000MHz signal generator with 1kHz frequency resolution:
A quick test showed a frequency about 3kHz too low on 144MHz. Needs adjustment or locking. This was at start-up, so it may improve.

A burn-in period test should be performed on all those units, to see how they work in a more stable state/environment, and then some more elaborate testing, maybe against some professional equipment.

After this, some radio construction can begin. This year should, first and foremost, be dedicated to antennas, especially adding some for monitor receiving purposes, and getting to transmit via QO-100.

After this, some microwave experiments, mostly local low power tests, and then some extreme low power experiments for different bands, ranging from MF to microwaves. The idea is working at least one QSO on as many bands as possible, with less than 1mW. Yes, micro-watts.

At some stage, some of the test equipment should be mounted in casings, mostly for protecting the test gear, and probably adding some RF shielding to the test gear. (inputs as well as outputs).

2020-01-19

Winter VHF Day, In Ringsted.

This annual winter VHF day takes place in the second half of January, and if I am not prevented by a family occasion, I will usually be going.

This year had a bit of a theme on OSCAR (QO) 100.

A nice presentation by OZ2OE and OZ5N showing some simple and less simple home construction projects for receiving the down link on 10GHz, as well as different versions of an up-converter to 2400MHz, ranging from some older home made (and modified for the frequency) 13cm equipment to a setup made with low cost Chinese modules.
OZ2OE was presented with an award, the VHF profile of 2019, mainly for his work on publishing information about how to get on the QO100 satellite.

Another presentation on the GPS control by Bo, OZ2M, I did not attend, but it does relate to QO100, in the sense that knowing your frequency (TX and RX) makes the satellite operation much more convenient, and with narrow band digital modes it is a necessity.

As usual, it is always a pleasure to meet friends, old and new, so I had an excellent time there.

2020-01-06

2m Tropo Over The New Year's Period.

Though I have had the cough and not too much energy, 2m has been good to me, mostly via FT8. When the voice is not good, it is a much better mode, and it is excellent for monitoring the propagation.

2m:
Coming back home on the 27th (I think) I noticed a cluster of spots from Southern France, all within a period of 10 minutes and in a relatively small area. This I consider a sporadic E opening, as other stations i Europe were working Es via a reflecting "cloud in the same area. My first experience of 2m Winter Es.
In the same opening LX1JX was worked as a new DXCC on 6m.
28th provided QSOs with 3 G stations and a PA. Not spectacular, but not too bad.
2nd January, just a single QSO on 2m with LY5P
5th gave me quite a surprise: I saw EA2XR in my FT8 display, only 17dB S/N, but I tried anyway. Much to my surprise he answered my first call, and the QSO was made. The surprise is more so, because he gave me a better report than I gave him: -6dB S/N. My guess is that I must have been lucky that he had his antenna precisely in my direction, and that his receiver is top notch (EME system?)
On 10m S01WS was worked.

All through this, I am surprised of the results using an omni-directional (Big Wheel) antenna on 2m, a long, lossy cable, and ... no preamplifier. There is plenty of room for improvement.

This is not a bad start of 2020.

2020-01-05

2020 Has Started, And A Brief Look Back On 2019.

For me, 2020 started in the sign of the cough. It stared e few days before the New Year, and is still there, though it seems to be subsiding now.

2019 was a year of travel, and not too much radio activities.
The QO100 geostationary satellite was activated, and the amateur radio transponder went on line in February. I got a decent system up and running for receiving the narrow band transponder down link. This is actually not too complex, as a TV satellite LNB is sufficient for converting the 10GHz down link signal from the satellite. A bit of modification, and adding an external reference oscillator placed indoors proved necessary, was constructed and has been in use since then. An improved version is in the making.
Next step is - still - getting to transmit on the 2400MHz up link for the satellite.
Also on 10GHz, a simple experiment has been running: Using a LNB for reception of terrestrial signals, via rain scatter and tropospheric propagation. I am still impressed that I receive a beacon about 36km from here, certainly non-line-of-sight. It is there all the time, received with the LNB alone, no extra gain from a dish.
Also, a fair amount of sporadic E openings over the summer on 6m and 4m, with a few new countries worked on each band, and getting a fair amount of components for projects (mostly via eBay).
Not too many projects finished, and many more ideas appeared. It is a fact of life that getting ideas is easy, putting them into practise takes much more time.

2020 should probably see me finishing just a few projects, like:
- QO100 uplink capability
- receive antenna system for monitoring several frequencies simultaneously
- some QRSS activity, mostly grabbing (receiving) QRSS signals  and other weak signal modes

The beginning of 2020 (and the end of 2019) has seen some spectacular tropospheric propagation over the Atlantic.
On 2m the European distance record was broken for tropo signals, with a spectacular QSO between Cape Verde and Northern Scotland.
On 70cm the world record was broken with a QSO from Cape Verde to Scotland.
All this has been made possible by using weak signal modes, like FT8. I would not be surprised if those records will be broken again later this year. Exciting times on VHF and UHF, and possibly the microwave bands.

Happy New Year to all from here. Hope to work some of you guys.