HAM Radio and the Corona Virus.

The western world is closing down, for a while.
The Corona virus crisis has hit us all.
As someone in the rather vulnerable group I have, essentially been in isolation for a week now. Not quite, because this week I had appointments at the hospital for a blood test and subsequent CT-scan, as part of the follow-up on a cancer I had treated - successfully - in 2018.

Since I was out, I did go to the pharmacy, too, just to get supplies of medicine I have been using regularly, especially a means to reduce the effects of pollen allergies.

This crisis may take longer than we might expect, for me, at least, I will hesitate to venture much out into the world (or even in my own country), until we have seen and tested a successful treatment or a vaccine is available.

What does that mean to me? I am fortunate enough to have retired, so there is no **need** to go out much. I can get food supplies and other necessities delivered to my door. Even then, I should be careful not to be infected from the delivery people. The most essential company has already initialized measures in that respect.

Here is the thing for me. I am generally used to living on my own, and have not gone out among people a lot. Yes, sometimes I have gone for a larger event, but that is all on hold now.

This is why I like having HAM radio as my interest, among others I can pursue alone. But with HAM radio, I am still in contact with other people on a daily basis, probably even more so because we are all at home most of the time.

So if I can avoid getting infected I will get through that crisis. Others may not be so fortunate.

To everyone in doubt: If you are an essential part of health care and other necessary functions, take all possible precautions to stay healthy. Many others should be working from home, if at all possible, and so help reducing the spread of the virus. Those of us who are vulnerable due to age or previous sickness, stay home if at all possible, and help in any way you can, those who need it.

We will all need to stand together (with a distance) to get through this. If we do, most of us will be there on the other side, if not, we will see much fewer people succeeding.


Analog Vs Digital Multimeters.

When should one use analog, and when digital meters for (mainly) voltage and current measurements?

To me there is an easy answer.
If I am adjusting something for maximum or minimum values, the analog meter wins every single time. It is much easier to see when the max/min values are reached with a "moving needle" meter.
Will I go without the digital multimeter? No way. It makes for an easy measurement of more or less static values.

So yes, I have a set of digital multimeters with Volt/Ampere/Ohm measurement, and one with capacitance measurement.
A cheap Chinese PCB module serves as L-C meter, down to most of the values I need to measure, about 1pF and some nH (I need to test the latter).

I just took out 2 museum pieces: Unigor multimeters. Good quality analog meters for V/A/Ohm, all the way into the Mohm range. The only thing is the battery needed for resistance measurement. Most modern meters use AA or AAA cells, or a 9V battery. Those 2 meters use 1.5V D-size cells. Now I need to find out if I can still get those. If not, I will have to find/make an adapter.
OK, the resistance measurement on the analog meter is not that important, but why not restore the full function of those museum pieces?

Apart from the multimeters I still have 3 excellent analog meters: An AC (milli)volt meter with high impedance input, a DC (milli)volt meter, and a Bolometer with a thermistor probe for up to 10GHz, one that needs care, not exceeding 10mW input to the probe, in order to keep the meter functional. More than 10mW, even for a short while, and the probe burns out.
A set of older (second hand) attenuators (for use with the Bolometer (power meter)) will have to be tested, but I have some, at least, new ones that should be good for low power measurements, up to 1/2 - 1W.

With access to the test equipment I should now be able to do a bit of home construction activities again, be it kit building or fully home made circuits.

I found an adapter for mounting AA batteries in the Unigor meters.
One of the Unigor multi-meters is now in working order. Ranges:
10uA - 1A
100mV - 1kV (DC and AC (the AC is probably not precise in the lower ranges))
Resistance measurement not very precise, but for that the digital multimeter will probably work better.
The other meter probably requires disassembly. If I get it back in order, I can measure up to 10A with that one. This is for later.


Desk With Test Equipment.

Finally, I did a bit of tidying in the upstairs shack.
The shack has two desks, one should be dedicated to test equipment, the other should be used for some radio and computer equipment.

I almost cleared the upstairs desk for the test equipment. At least, the desk can now be used for more extensive testing than with the rudimentary set of test equipment at the ground floor radio (shack) desk.
Test equipment available for use at the desk:
- HP DC voltmeter
- HP AC voltmeter
- HP432 bolometer w/10GHz probe
- spectrum analyzer 10 - 1700 MHz w/tracking
- Marconi transceiver tester
- Tektronic 2 channel oscilloscope, 60MHz
- Velleman frequency counter
- modulation meter
- handheld multimeter, V/A/Ohm
- old Trio AF signal generator
- Fluke V/A/ohm, not functional, will need check and repair, if applicable
- Of course, (Velleman) soldering iron w/ power supply and multimeter
- a diode power meter built by a friend. can do 10GHz/max 100mW

There is more to come, e.g. a bit of test equipment/accessories for microwave and other measurements, such as:
- low frequency function generator and mini (cheap Chinese LF) oscilloscope kit
- modified satellite or MMDS down converters for converting microwave signals down to the range of the spectrum analyzer or frequency counter(s)
- VNAs (mini or Nano) for circuit/antenna testing (gain/frequency characteristics, SWR etc)
- directional couplers for 1.3, 2.4 and 10GHz
- Accessory mini frequency counters
- reference frequency generator ( TCXO, OCXO, Rubidium or GPS controlled)
- crystal tester(s)
- and more, to be described later


Second Crystal/Ceramic Resonator Tester. Update

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.

A third version with 2x 100pF in the Colpitts oscillator was built. This appears to work nicely from 2 - 16MHz with crystals.
Ceramic resonators:
- The 3.5 - 4MHz range works well with some resonators, no filters.
- The 7.16MHz (3-pin) oscillates nicely just under 7MHz with the capacitors in the oscillator.
- 12MHz resonators oscillate fine.
- 5.5MHz filters do not oscillate at all.

My conclusion is that the three testers combined will provide some crystal and ceramic resonator/filter tests, but a dedicated (set of) oscillator(s) and a dedicated frequency counter with high impedance/low capacitance input is most likely necessary for a better test system.


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.


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.


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).