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. 

Ground connection for the Mini Whip. RX Test.

 I have a ground rod on the Mini Whip now. Not too far into the ground, about 60cm/2ft. Hammering a 2m (8.5ft) ground rod is tricky without the right tools ;)

The results are interesting:

A relatively detailed review was done today, by dialing slowly through the bands. Starting downwards from around 18MHz indicates that the sensitivity/SNR has improved reception on frequencies from about 1.8MHz up to 18.2MHz, maybe higher.

Medium wave is not bad, with signals on essentially every channel in the whole band, with a reasonable SNR, probably increased sensitivity.

NDB band appears noticable worse wrt SNR, possibly partly due to overload from MW stations in the evening, but noise level seems to have increased.

LW seems OK, not spectacular.

VLF (<100kHz) seems more sensitive, but with more noise. possibly due to overload of the RX. 

A different Mini-Whip with a real whip antenna (1 - 3m long) might improve sensitivity on VLF/NDB bands, but should probably have a low pass filter with a 3dB cut-off frequency of 530kHz. Because a thin whip mounted low is not too visible I might add this to my antenna farm, just to see how it works. If it works well I can make a permanent installation.

Because the Mini Whip is very broadband it may be an advantage to make some filters in any case, possibly as follows:

Low pass with 150kHz 3dB point, for the 136kHz amateur band and "VLF" reception.

Band pass with 150kHz high pass and 530kHz low pass, mainly for the NDB/marine bands and 472kHz amateur band.

MW band pass with 530kHz high pass and 1700kHz low pass.

MF band pass with 1700kHz high pass and 3MHz low pass, mainly for the 1.8MHz amateur band.

HF band with 3MHz high pass filter.

If I get all working nicely I may make a (set of) distribution networks, possibly with switches for the different receivers.

Yes, I like monitoring a lot of frequencies I do have some receivers, everything from purchased amateur equipment to portable transistor radio(s) with external antenna input(s), and, of course some SDRs, and some simple monitor receivers (e.g. a Pixie kit for 40m), and some that I may build. At some time I have been monitoring (audio or data) on 14 different frequencies simultaneously, part of it as monitoring propagation, and I expect this record to be beaten ;)

This is also part of my intention to make a contact on as many bands as possible with (at least partly) home made equipment.

Another Receiver on the Mini-Whip. VLF Reception.

 For a few days I was using my old FRG-100 with the Mini-Whip. The receiver appears to have a rather wide IF filter, meaning that I could hear a carrier all the way through zero-beat (part of the other sideband audible) Not good for listening to AM signals.

Also the lowest frequency I can receive with the FRG-100 is 130kHz. I would like to listen to lower frequencies.

Enter an old AOR AR-7030 I have. I think, according to the specification, the receiver covers 30kHz to 32MHz. Very nice, even if I wanted to test it on a lower frequency. Actually, the AOR frequency dial goes right down to 0kHz. Well not really. on the very lowest frequencies it is totally deaf (no surprise).

Tuning upwards with the Mini-Whip connected the noise starts coming up around 10 - 12kHz. Now it gets interesting. The lowest frequency signal I could receive (until now) is on 16kHz (origin unknown). This means that I should be able to receive the SAQ transmitter from Grimeton, Sweden, next time it has a transmission.

Further, the filters in the AR-7030 are clearly better than those in the FRG. Mounted in this RX are IF  filters with bandwidths from 2.1kHz up to 9.5kHz, in several steps, and also tone controls for bass/treble. There are even better filters in my transceivers, but those have a lower frequency limit of 30kHz or more.

Never the less, VLF signals from as far away as Grindavik, Iceland on 37.5kHz were heard in the day time. Strictly speaking not VLF, but definitely a nice reception. This is a data signal that I did not attempt to decode.

The station in Cutler, Maine (US) was not audible with this set-up, but then again, the antenna is not yet optimized for lowest local noise level. The weather and other activities have been in the way of connecting a ground connection to the antenna. and other steps.

Tuning up through the band, all the way up to 518kHz NAVTEX frequency I now come across a lot of signals. In particular I now hear more NDBs (non-directional beacons used for navigation) in the 300 - 500kHz range, along with other signals of unknown origin (to me at least)

One surprise was a signal on 505kHz:

OK0EMW in JN88ks running CW identification (with Locator) and some QRSS, too.

This must be a remnant of the activity that was allowed on experimental basis on the "old" 500kHz band. I was not aware that there was any activity there any more. Apparently the (QRSS) etc beacon was allowed there those years ago, and the permission has not been revoked.

There is much more to do regarding MF, LF and VLF reception. One thing is to test if I can really hear the SAQ transmission next time it will be active.

Another test should be using my IC-7600 for reception on LF/MF. With the much better (DSP IF) filters reception of many more NDBs and other signal should be possible. There is a lot of noise in that part of the band, so every improvement of the receive side will count. Also, a set-up with a low frequency SDR should be done. The first SDR experiment should be with the RTL-SDR in direct sampling mode, then maybe later I will get a more suitable SDR, also for those frequencies

For the lowest frequencies a test with a computer sound card should make reception up to 24kHz possible, maybe even up to 48kHz with 96kHz sampling.

Active Receive Antenna: The PA0RDT "Mini-Whip". First Experiments.

 A little while ago I purchased a Mini-Whip set (the outdoor unit and the bias-tee) from Chine. Quite inexpensive, and now when the weather is improving (some days, it is April, after all) I started an experimental set-up.

I was aware that I should avoid noise from entering the antenna via the outside of the coax, so the first step was using a common mode choke (CMC) at the antenna, with a low cost (green) EMI toroid from China.

The antenna is mounted on top of a 4m long telescopic fibreglass mast, intitially just attached using duct tape, placed at a relatively low noise point in the garden with more or less optimized distances to all surrounding houses. This is sufficient for the testing and can be changed later. The power supply is a battery, just to avoid noise entering directly the system via mains power.

The result was quite disappointing, but not entirely unexpected up to 7MHz there was a substantial noise floor, reducing the signal-to-noise ratio (SNR) when compared to a multiband dipole I have in the garden, and the noise level on medium and long wave (MW, LW) was killing all signals less than S9 Even then, and this was encouraging, more than half of the MW frequencies showed audible stations before sunset.

Next step: Adding a "SW" CMC just next to the bias-tee. This was using a FT 240-43 toroid core with 2x10 windings of RG-174 coax. Progress: The noise was reduced on SW, now the Shannon VolMet on 5505 was audible with a decent signal, not quite as good as with the dipole, but a definite improvement. MW was still quite noisy, and LW not good enough. Very few NDBs (Non-directional beacons, mostly situated at airports) were audible in the 300 - 500kHz band. signals on 472kHz were still drowning in noise.

Yet another step: A second LF CMC was added (one more of the green Chinese toroids) was added, making MW quite usable, though not perfect.Several NDBs popped out of the noise, and with better filters in a receiver there would probably be many more to find. The usable frequency range was extended to 400kHz up to at least the 30m amateur band at 10MHz. The Shannon VolMet now has a SNR comparable to the dipole. Good progress.

This is the state of affairs at the moment. There is still too much noise for my taste, but at least I can work on removing noise coming from my own house.

There is more to try:

1) adding a second (MF/SW) CMC at the antenna. This is not too difficult.

2) Adding a ground connection directly to the ground of the Mini-Whip PCB, "bypassing" the CMCs at the antenna.  This will take a bit longer because good weather is necessary if I want to solder outdoors. As an alternative the antenna could be dismounted and the soldering could be done indoors. Further, a 2m ground rod should be hammered down.

Still more to do with this receive antenna system, but it is a decent start

Test Equipment part 1: RF Signal Generators.

Working with transmitters, receivers and antennas is not easy without test equipment. Sometimes a quick test can be done with your transceiver, or a receiver. More detailed testing requires more. I would like to build equipment for up to 10GHz, at least, as well as going all the way down to 136kHz. Optical communication would be nice to try, but this is outside the scope of this post.

Now, for testing a receiver (part), some kind of signal generator is needed. It is always nice to have the generators calibrated, but for amateur use less can do it.

Excluding using the transceiver, there are a few options for very simple and low cost test generators:

1) Low cost Chinese PCB modules. I found:

a) 0 - 5MHz function generator. It is using a DDS, meaning that the stability is essentially as good as a normal crystal oscillator, no calibrated output level, though, just a potentiometer.

b) 0 - 55MHz signal generator with a DDS, same limitations as above, but no level regulation at all.

c) 35 - 4400MHz generator, with same limitations as the one above.

This will create a usable signal for use up from close to DC up to 4400MHz. Using a harmonic of the 35 - 4400MHz it is quite possible to generate a signal usable for testing if a 10GHz receiver is functional at all. These modules can probably be purchased for less than $100 on Ebay. Not bad for a simple setup. I do have such a set of modules, but I decided to go up one step. Yes, somewhat more expensive, but easier to use. 

There is one more option for a low cost signal generator: The NanoVNA.

This VNA comes in 4 different frequency ranges: 50kHz - 900MHz, 50kHz - 1000MHz, 50kHz - 1500MHz and the NanoVNA version 2 (SAA 2) with 50kHz - 3000MHz. The output of those are not all too clean, but they will all provide a signal that is sufficient to test the rough function of a receiver, or as a test oscillator for a transmitter.

2) My signal generators:

a) FY6800 DDS signal generator/unction generator up to 25MHz. output not calibrated in dBm or microvolts, but it can deliver up to 25V, as far as I recall. could be used as a test exciter for a transmitter, too. This one covers the low bands very nicely, and I can use attenuators for testing receivers.

b) 500kHz - 470MHz generator. This one has a sufficiently calibrated output level, and delivers up to -73dBm, the equivalent of an S9 signal in a receiver. A bit low, but fine for testing that a receiver is not defective or completely out of alignment. I could add some amplification to increase the level, and I will do that if I find the need.

c) TPI 1002A generator. This is built by a Texas radio amateur who runs the company RF-consultant ( www.rf-consultant.com ), and covers 35 - 4400MHz with a calibrated output level from very low up to over 10dBm. The generator is controlled via a USB cable needs a computer running Windows, at least XP. I ran a quick test of the generator at 2400MHz, using a (long ago) calibrated power meter, and the levels were nicely corresponding, and therefore good enough for my use. The generator can be programmed to optimize the output for low spurious output or low (sideband) noise output. very useful for many measurements on these high bands.

d) a small box with a Chinese built ADF 5355 generator capable of generating signal up to 13600MHz, yes 13.6GHz. The unit can be used independently, but I think that it can be controlled via the USB port, too.

Why not use surplus (professional) test equipment? I have had some of this, but space (or cost for newer, smaller equipment) does not allow for this in my case. Yes I do have a bit of this kind of equipment, but no longer for (RF) signal generators.

Why did I not try to build this kind of test equipment? First, it would take me far too long, and I would need access to calibrated test equipment to get them working properly. Second, my priority is to build some (not too complex) transmitter and receiver equipment for all amateur bands from 136kHz to 10GHz, I have got the idea that I want to try to make a QSO on every amateur band available to me with home made or modified (surplus or not-designed for amateur radio) equipment. For now, I have only done this for the 3.5, 5.2 and 7MHz bands, so there is some work to do.

More Scatter on 10GHz.

 My 10GHz receiving setup is still very simple.

Consisting of a modified LNB at 4m height (better frequency stability because the reference oscillator for the PLL is inside the living room). No dish or additional horn antenna. Indoors the signal is fed to a AR-8600 receiver receiving the IF of 618MHz.

With this simple setup I can hear 2 beacons, OZ7IGY at 26km and OZ9GHZ at 36km distance.

Most of the time OZ7IGY is quite weak (S2 or so) due to the landscape blocking the reception, but either tropo-scatter or reflections on high voltage lines/masts provide this signal.

When we have rain, even light rain, the signals are enhanced, sometimes up to S7 or so.

This winter I have also seen snow scatter. It sounds much like rain scatter.

When I get a better system up and running, directional (horn or dish) antenna, and a transverter, I will have to see what can be heard and possibly contacted further away. Even if my location is not very good, I suspect that some QSOs would be possible with the 2W amplifier I plan to use. Because of  visibility, I do net expect to work with a big (1m) dish up in the air, so I will have to see what can be done with less. Some directions will be OK at my location, others will be very difficult, but using scatter events I should be able to do a little.

I suspect that my first 2-way tests should be made with a 17 - 20dB horn antenna. Not ideal, but one step at a time.

For monitoring the band I may set up a box with 2 or 3 LNBs (switchable) with SDR back-end, for wide angle monitoring of beacons and activity on the band.

QO-100 update.

 I have added an extra receiver to my QO-100 setup.

In addition to the "normal" (knob-tunable) receiver I now have a RTL-SDR connected to the LNB IF output, too.

Being able to see the whole spectrum of the narrow band transponder makes finding signals a lot easier. I know that there a re web-SDRs that can be used for that, but I like being independent on the Internet when working with radio. Receiving signals via a web-SDR is cheating to me ;). Until I get a better, more stable and accurate reference frequency, I do find the web-SDR a good tool to get my TX signal on a pre-defined frequency, though.

Also, I now have a constant overview of what is going on on the NB transponder. 

When the weather gets warmer, and it gets easier to meet up, I expect to improve the receive set-up, so DATV reception on the satellite should be possible. But DATV is for later. Also, if I want to transmit 

DATV on QO-100, I will need quite a bit of power output, and a better feed antenna for my 110cm dish.