472kHz I/Q-SDR kit

Nothing is for free, up to now, there is no kit available for 472kHz.
However, there is one for 136kHz, which can be easily modified to match the new band.
Check out box73's longwave I/Q-SDR kit.

You will see that a 15MHz signal is divided by 25. This results in a 600kHz signal which is further divded by 4 in order to create the phase shift. All in all, this ends up in a center frequency of 150kHz.

We can use the same oscillator and divide the signal by 8. This results in 1.875MHz, which will be further divided by 4 providing a center frequency of 468.75kHz.
With a sampling rate of mere 24kbps, or +/- 12kHz bandwidth, the entire band (472 to 479kHz) will be covered.

The digital part is rather simple to modify. A suitable ripple counter could be the 74HC93.
The frontend is even more simple... just pick a 455kHz i.f.-filter/transformer and replace C1, C2 and L1.

Should the old experimental range, somewhere above 500kHz, be a desired range, the additional modification would simply replacing the 15MHz canned oscillator with a 16MHz one.

I will see if I can persuade the OM at box73.de to provide such a kit.

MF/HF Aerial

And along came an idea....
You may have heard about the CobbWeb aerial. Essentially, this is a cluster of dipoles for the bands 20m, 17m 15m, 12m and 10m. The cluster is fed via a coax choke.
Maybe there is a way to squeeze more out of this aerial. The amount of wire in the dipole array creates a decent capacity, I figure.
It may be worth a try to build such an aerial, feed it with RG-6. And, for MF purposes, use the feedline's shield (and core) as vertical and the dipole array as capacitive load. The rf choke could further help to increase the load on the (very) short Marconi for 600m.

This would be somewhat like the antenna disclosed in the U.S. Patent 3,569,970, (see Figs.7a,7b) but using the CobWebb in place of the stretched dipoles.

472kHz Phasing Transmitter

We have seen that a 1.8432MHz oscillator will provide us with a 460.8kHz I/Q-SDR LO.
This is very much in a comfortable range for of the new amateur radio MF band, i.e. 11.2kHz to the lower band edge and 18.2kHz to the higher band edge.
Now, how to generate the modulator signal? Phasing style, the easiest would be to build an oscillator for the 44.8 to 72.8kHz and use two Flip-Flops to generated the 90 degrees phase shift.

1. Such an oscillator could be a rather simple function generator. Other solutions could be based on micro-controllers such as PICs, PICAXE, AT-Tiny, etc. With such a controller, it would also be possible to program features like memory channels, frequency display, beacon-keyer...
2. Another approach would be to build a crystal oscillator, using cheap industrial xtals, and divide it down. Some ideas could be crystals from the XMHz range divided by N (by means of a binary counter) before feeding the Flip-Flops:
• 3.000MHz / 64 = 46.88kHz resulting in 472.5kHz
• 3.072MHz / 64 = 48.0kHz resulting in 472.8kHz
• 3.2768MHz / 64 = 51.2kHz finally resulting in 473.6kHz
• 3.579545MHz / 64 = 55.93kHz resulting in 474.78kHz
• 3.6864MHz / 64 = 57.6kHz resulting in 475.2kHz
• 3.93216MHz / 64 = 61.44kHz resulting in 476.16kHz
• 4.000MHz / 64 = 62.5kHz resulting in 476.4kHz
• 4.096MHz / 64 = 64.0kHz resulting in 4768kHz
• 4.194394MhZ / 64 = 65.54kHz resulting in 477.2kHz
• 4.433619MHz / 64 = 69.28kHz resulting in 478.1kHz
3. In the light of the above, ham-radio crystal such as (in MHz) 3.530, 3.535, 5.540, 3.550, 3.555, 3.560, 3.575611, 3.880, 3.885 can fill in gaps. Those crystals are found at box73.de "expanded spectrum systems".
4. With some luck, one finds tons and tons of surplus crystals in the range of 2.8672MHz to 4.6592MHz. As I recall, there where channelised commercial transceivers (e.g. military, maritime etc.) making use of crystals in that range.
5. Similar to the crystal approach, one could consider to use 3.58MHz, 4.0MHz, 4.19Mhz, 4.50MHz and 4.91MHz ceramic resonators for a VFO. The 6.00MHz, 6.50MHz and 8.00MHz resonators would require one additional division.
6. The deluxe version of it all would be a DDS for the range 2.8672MHz to 4.6592MHz. I wonder is there is any kit in which the LO offset can be easily programmed to (f/256)+460800Hz. Maybe a project with the DDS60 board.

When modulating the phase shifted AF signals, one has to consider that those are essentially square waves. In order to reduce harmonics, it would be required to do some severe low pass filtering at about 19kHz before injecting the signals into the I/Q mixers.

As to receiving, the 11.2kHz to 18.2kHz is in the comfort zone of any 48kbps sampling sound card.

There you have it, my presently preferred solution for the new 600m amateur radio band.

600m Signal Source

As we know by now, 472-479kHz it will be. In an earlier post I revealed some "cheap" frequencies which would mix into the new band.

Some further options using industrial crystals:

DigiKey sells a 4.754687MHz crystal... count to (divide by) 5 and further divide by two results in 475kHz. A super-VXO could be an option here.

The above mentioned count to 5 solution applies to the following crystals, found at the same source: 9.494531MHz, 9.509375MHz and 9.545MHz. Other crystals would allow for an out of band I/Q-SDR LO: 9.600MHz, 9.625MHz and 9.7941MHz. Here, the chain would be count to 5, divide by 4.

Further: 18.9375MHz, 19.0625MHz  and 19.069928MHz and for I/Q-SDR: 18.869MHz, 18.8696MHz, 19.200MHz, 19.280MHz and 19.440MHz. Consequenctly, the chain would be count to 5, divide by 8.

Plus: 28.59375MHz, 28.5938MHz, 28.636MHz, 28.6363MHz and 28.63636MHz (count to 3, count to 5, divide by 4).

Taking it even higher: 38.000MHz and 38.00053MHz (count to 5, divide by 16). I/Q-SDR: 38.400MHz and 38.880MHz.

Also found at DigiKey: a 7.680MHz crystal. Divide by 16 results in 480kHz. Again, a super-VXO and some (severe) down pull should generate a signal in the band. This crystal provides easy access to I/Q-SDR: LO spot om 480kHz, even a mere 24kbps sample rate would cover the whole band. The same applies to the 15.360MHz found at the same store.

All the above mentioned crystals are of industrial kind. One option would be order one for the favorit solution, the other option would be to carefully watch out for those frequencies before dumping old computers & Co.

600m SDR RX (TX)

As we know, presently there are a couple of frequencies of the 600m band open to amateur radio operators.
Most of authorities allow transmission somewhere above 500kHz. In The Netherlands the permitted range is 501-505kHz. In the future, depending on the decision of the WRC12, this will possibly change to 472 to 480kHz. The U.S.of A. proposed the following ranges 461-469 and 471-478 kHz.

Lets look at the (inexpensive) option the box73 SDR. The 80m version of this receiver uses a 14.000MHz oscillator. Operation on the 600m band can be achieved by changing the front-end filter and the SDR-LO.
Considering 48kbps sampling, the LO-frequencies would be the following

• QRG: 470kHz - LO: 1.843MHz
• QRG: 500kHz - LO: 2.000MHz

This will result is RX-ranges of:

• 460.8 -/+ 24 = 436.8 .. 484.8
• 500.0 -/+ 24 = 476.0 .. 524.0

Concluding, a decent 600m receiver can be built with LOs using regular canned oscillators.

600m with CB-XTALs follow up

Hi there... I am back!
Presently, amateurs in The Netherlands are really happy, not only have we got the permission to transmit on 4m, we also may transmit on 600m again. For the time being between 501 and 505kHz.
For this range (well, to the upper QRG of 504kHz) this article could lead to a cheap signal source.

However, in about a month's time, we will know is we need to redesign our exciters, i.e. to the range 472 to 480kHz. So, lets have another look at the cheap crystal solution.
The new range is not that easy really. One solution would be the mixing of two standard xtal frequencies:

• 4915.2 - 4433.6 = 481.6 somewhat high, could be pulled into the range

A spot on solution would be a 10m QRP crystal (28.060MHz) on its fundamental mixed with a 9.8304MHz standard crystal:

• 9830.4 - 28060/3 = 9830.4 - 9353.3 = 477.1

Another spot on option: a 40m QRP crystal, mixed with a 6.5536MHz standard xtal.

• 7030 - 6553.6 = 476.4

Starting from lower frequencies, crystals from box73.de:

• 14745.6 - 14270 = 475.6
• 7025 - 6553.6 = 471.4 (pull!)
• 3550 - 3072 = 478
• 4000 - 3530 = 470 (pull!) (*)
• 3555 - 3072 = 483 (pull!)

Subractive mixing has the advantage that some thermal effects may cancel. Assume to us several standard crystals in a super-VXO.
Mind you, the higher the frequencies, the easier to pull, i.e. create a nice tuning range. However, lower frequencies will give better stability.

(*) Note, there is a 4.00MHz ceramic resonator, which will allows for a nice VFO. Use a Pierce oscillator to obtain a QRG above the ceramic resonator's series resonance.

SDR Meets DJ Gear

Hi there! Some of you may know that I am quite busy with music, dance and the stuff concerned.
Some rare occasions have it, and hamradio mixes with music mixing, aka DJing. And here is one of those occasions:
The DJ Mouse
http://www.dj-mouse.com/
Basically, there is nothing special about this mouse, other than the regular scroll wheel is somewhat wider and parallel with a jog wheel. It is just this jog wheel that makes all the difference.
All SDR software solutions I am aware of, are using the scroll wheel for sweeping the frequency. I always felt that this was somewhat awkward. Now we got a mouse with a rotary encoder, just like a VFO knob.
Still I scratch my head what can be done with the "scratch" button...

Central Heating Aerial

Dear readers, there was not much going on here lately, sorry about that!
Today, some weird incident triggered another thought in me.... and here it comes:

Returning home, I felt an unfamiliar chill in my house... That's no good, I thought, and checked the central heating system, which indeed was dead. Quick check and the culprit was found. The expansion vessel (expansievat, Ausdehnungsgefäss, vase d'expansion, whatever you wanna call it) leaked. The local hardware store was still open, hence I hurried up to get a replacement of similar size.
Just €22.- will get you one with a 17l capacity.
Speaking of capacity, that came to my mind on my way back home. What about using the defective one as top-capacity for a short vertical? The roundish things got a nice thread which would easily fit Cu pipes and respective fittings.
The vessel itself is made from steal (Fe) most likely. OK, that's somewhat on the heavy end, electrically however, not that inferior to Al, which is used most.
The plan is to build a short tapered vertical from Cu-pipes with an expansion vessel on top.
I figure, one may also consider a short loaded dipole.
Possibly, just 2 of such vessels could make a broadband dipole for VHF.... one could also think of a broadband vertical for VHF, using just one vessel on a ground-plane.

There may just be one down-side, your neighbors will think you're completely mental, putting the expansion vessel of your heating system 5m above your roof ;-)

Happy experimenting.

Most Interesting

What is going on here? A local station, a dx station and the radar, which seems to dislike the condx...

Broad-Band Aerial Update

Short update on the 11m half-wave aerial conversion.

The 4:1 UnUn is placed, that was one of the two options. Actually, this was the easy option, since the UnUn came wound up and ready to use from a surplus dealer.

11m half wafe aerial base portion

The arial, about 5.5m long, w/o any further modification could be matched easily with the IC-703 builtin tuner on the band from 80m to 10m, with the exeption of 30m. I figure, some additional Al-tube extension could solve that problem.