Test Equipment, Part 1a: Idea Box: Using Nano VNA as a Portable RF Signal Generator.

 Not everyone can afford expensive RF signal generators, or even several less expensive ones, so here are some thoughts on how to make simple signal generation with a Nano VNA, probably the least expensive piece of test equipment with excellent functionality for the amateur who wants to build some equipment, or even just as an antenna analyzer.

In my case I want to be able to check receivers up to the 10GHz band, maybe higher, so what to do with a simple Nano VNA?

I have been looking a bit around to see what others have done in this regard, so here is my 

Up to the 70cm band.

For the 2200m to 70cm bands, even the oldest version of the Nano VNA can be used directly. Even though it does not have a calibrated output (amplitude or frequency) It will provide a (not very clean) signal, but if you know which frequency your receiver is set to, it will work fine. If the signal is too strong it is possible to use attenuators, for the HF bands and lower they can be home made, it is more difficult on higher frequencies. 

It is also possible to use the VNA as a "personal beacon" test generator, though a keying circuit (and amplifier) has to be added. What about your own low power CW transmitter? Mind you, some filtering will be necessary, as the VNA signal is not really clean, but for an experiment it will work.

Higher bands.

The simplest way to generate signals on the microwave bands will be a simple diode multiplier (comb generator).

So here we go: Add an amplifier followed by a 3 - 6dB attenuator to the signal generator output. It is likely a good idea to add a simple band pass filter as well. Then connect a diode across the output of the attenuator.

Why the attenuator, you may ask. This is in order to have a good load of the amplifier, giving a more stable output.

Next question: Which kind of diode can we use? Given what others have done, with sufficient input power into the diode, PA3FYM reports + 7dBm is sufficient to generate a 10GHz signal using a standard (dirt cheap) 1N4148 silicon diode, so that is what I would try first. Others suggest using step-recovery diodes for generating stronger harmonics, but why do that if the low cost solution works.

With a 432MHz (filtered) signal from the Nano VNA, signals should be generated on 1296, 5760 and 10368MHz, providing signals for narrow band receivers. About 437MHz will provide a signal in the QO-100 satellite downlink band on 10GHz, and should be within range of the band pass filter.

With 400MHz a 2400MHz signal can be generated.

With 425MHz a 3400MHz signal can be generated.

This covers all amateur band allocations (up to and including the 10GHz band) available to me, and should be sufficient to check receivers on all bands, if no other (better) RF signal generator is available.

Given the relative simple design of this I might try it out. I can test the 10GHz signal with a (synthesized) Satellite LNB, initially I will test without a filter on 432MHz, just to see if it is necessary. I might even try to connect the diode directly to the output of the Nano VNA Simplicity rules ;)

All this is with the cheapest version of the Nano VNA. As you may be aware, there are versions with a larger frequency range. The SAA2 (Nano VNA v.2) works up to 3GHz. More expensive, but much easier to work with, up to and including the 2400MHz amateur band. The diode multiplier should also be useful with this model.

The Tiny SA (spectrum analyzer) should be able to work as an RF signal generator, so this might be useful as well, if you have one.

One other option may be using the generated signal from a scalar network analyzer (35 - 4400MHz. I do not know if the spectral purity is sufficient for those PCBs, or if the frequency can be set to a fixed value, but I guess this has to be tested, too. First more research on the Internet. If this one works, the 3400MHz band will be included, but no HF/MF/LF. Everything is a compromise.

2m Es Continues.

 This year's sporadic E season could turn out to be the best in my experience.

Yesterday, June 11th, I had the highest number of Es QSOs in a single day on 2m.

4 different stations in Southern France, one in SSB, the others in FT8, and a single Spanish station, EA1SA in IN83.

I am hopeful there will be more. 

This year I have been focusing more on the 2m band than on 4m and 6m when the chances look good, and it has been successful, even if I have missed openings - sometimes by mere minutes.

I have made good use of PSK-reporter and DX-Maps. Even when I was not at the radios, I can monitor the propagation on a separate screen in the house, and that pays off nicely. Of course, when I am away from the house I cannot immediately go to the radio, but at least I know if something interesting has happened while away.

Of course I want to make some contacts with this rare propagation, but I do not want to be tied to the radios all the time.

2m Sporadic E, and a Transatlantic Opening on 6m.

 The late afternoon today had a nice Es opening on 2m. Stations received were EA1. EA3, EA6 and IS0.

I managed a single QSO with EA6SA, and I was called by another EA6, but no complete QSO.

All with my omnidirectional "Big Wheel" antenna, so I am not complaining at all.

After finishing reading a book I noticed that the 6m band was open to North America. While I did not work any of the stations with my limited power, 80W into an omnidirectional vertical, the Diamond 3-band antenna "V2000", A lot of stations from Florida and Texas in the South to Wisconsin and further East in the North.

I really need a better antenna for 6m, one that can take the power from a power amplifier. I do have one, but it has been put away for the time being, because the antenna is only rated to 150W, and I do not want to lose it.

All in all a very interesting day of sporadic E.

Here is a thought. When looking at my logs through the years, there is a tendency to have 2m Es openings  at my place more often around two sets of dates, about 8th - 10th June and 8th - 10th July. This could be a coincidence, but it does coincide with meteor showers at those dates, so who knows? I do not.

I am well aware that the cause of sporadic E has many other (unknown) factors, but it is a thought I have had for some time.

The Sun Is Awake!

 This past week end we got the clear sign that Cycle 25 has arrived.

Saturday we had the first X-class solar flare of the cycle. The X-class flares are the strongest category of solar flares, and if they are located near the centre of the solar disk, they can create strong auroras and other disruption in HF propagation.

This flare was near the edge of the disk, and will not produce auroras. Id did, however create a sudden ionospheric disturbance (SID), in essence a short wave radio black-out in the day time zone of the planet.

This time the timing created the black-out in trans-Atlantic propagation.

While the cycle has let us wait quite a while, I think that this autumn/fall we will see the higher HF bands (10 - 20m) wake up and become very good. 

With the advent of weak signal modes I think that world wide openings will be quite common on the 10m band, and CW QSOs will certainly be there some of the time.

According to predictions the maximum should arrive in about 3 - 4 years, so I am looking forward to better days for HF propagation on the higher bands.

Who knows, with weak signal modes like FT8, we may see openings appear in the 6m band during the maximum. 

Some 2m Sporadic E (Es).

 Yesterday my FT8 monitoring system detected a single Italian station, most likely a short Es opening, or a long meteor burst.

Then this morning I went to the radios and found that 10 minutes before there had been Es signals on 2m. 2 stations in Southern France and 4 stations in Northern Spain were detected with up to +11dB S/N.

Away from the station I have set up a rudimentary 2m Es monitoring system using the PSK-reporter and the DX-maps websites showing my own 2m FT8 spots and the Es-MUF map for Europe, as well as stations spotted on 6m FT8.

This monitoring system has been running essentially 24/7during the Es season, and I would like to be able to add to the system, so I can monitor 28(/40)/50/70/144MHz 24/7, especially during the Es season, so here is an addition to the "Idea Box":

For this I do have usable receivers, but the antenna system is not yet ready for this. For the purpose I am thinking of mounting a TFD (Terminated Folded Dipole) vertically, with an added broad band amplifier, hidden in the trees at the far end of my garden, at least for the 28 - 70MHz bands, and probably some kind of wideband antenna, usable for the FM broadcast band, air-band, 137MHz satellite band and 2m, also with a preamp.

An alternative for 2m would be a simple vertical or a horizontal V-dipole or a halo, with a narrow band preamp for 2m.

Home Antenna Considerations, Part 1.

 I am doing some considerations on a re-design of my antennas in and around the house. Right now I have a more or less functioning system, because during the pandemic I have not had the option of people coming to assist in antenna installations. 

The antenna system was due some maintenance the last 2 years, so now is probably the time to get started again.

This is my existing antenna system:

1) RX-ant:

- Active Mini-whip: 10kHz - 25MHz (needs some distribution/filter circuit(s))

- Indoor loop: 500kHz - 30MHz (lower than 500kHz w/amplification?)(needs distribution/filters)

- Loop on ground (30 - 160m, maybe MW/NDB bands w/ amplification?) (needs distribution/filters)

2) TRX-ant:

- R6000 (10 - 20m) (6m poor(RX only?)). In working order, but guy wires need to be replaced.

- Low 5B dipole (10-15-20-40-80m). Not very efficient due to the low height.

- V2000 (6/2m/70cm vertical). This is in working order.

- Corner vertical (mounted at the corner of the garden). This antenna has lost the top. I will have to check if the telescopic fiberglass mast has partly collapsed, or if it is broken. Originally this antenna worked in varying degrees on 160 - 30m, but it has certainly lost the 160m capability. Most definitely needs maintenance or re-design.

- Big Wheel, 2m (could possibly do 70cm) Omnidirectional, horizontal polarisation. This is generally in working order, but in rainy conditions it seems to deteriorate. Probably leaking, so needs maintenance.

- 10m 1/2 wave antenna. In working order.

- Low 2m/70cm vertical w/lossy cable. 

I am trying to make the antenna system as unobtrusive as possible, still with the functionality I want, so here are some requirements:

TRX Operation possible on following bands:

- preferably a possibility og making at least one QSO on 2200 and 630m. This may be tricky, but should be tested.

- 10 - 160m, reasonably well.

- 10m good (minimum as good as a vertical 1/2 wave).

- 4/6m needs to be improved (probably with Moxon, capable of running more power)

- 2m added gain, horizontal

- 70cm horizontal gain

- 23cm vertical and horizontal w/ some gain

- 13cm vertical and horizontal w/ some gain

- 9cm ???

- 6cm (maybe "14dB" patch array)

- 3cm 15/17dB horn or small (35cm?) dish

- probably some antennas should be capable of more than one band.

Diverse RX antennas: 

- Mini-Whip (2 pcs?). Will need distribution/filters

- Indoor WB loops for MW/HF. Will need distribution/filters

- Outdoor WB loop for MW/HF. Will need distribution/filters

- Outdoor loop for MF/LF(/VLF?). Will need distribution/filters

- Loop on ground antenna for MF/low HF bands. Will need distribution/filters

- other possible RX antennas may be considered, e.g. 4/6/10m RX antenna, 137/145/250MHz, 432MHz, 23/13/3cm monitor antennas.

I do have some ideas, but I think I will have to take yet another look at the garden and assess the possible solutions, so this is all for today.