Q-RX - a 600m Receiver Concept

When searching the internet, I found the QTX by GW3UEP. The exciter of this transmitter uses Q4 (pin 7) of a 4060 ripple counter. Q4 is the lowest division available with the 4060, hence, an 8.0MHz ceramic resonator needs to be used to generate a 500kHz frequency. The nice thing about the 4060 is its' internal oscillator.

So, here is the concept for a 600m receiver. Use a 4060 in the way as it is shown for the QTX. Generate a 250Hz frequency with it as a LO for a subharmonic mixer.
There are two obvious options to do that:

1. 8.0MHz ceramic resonator - Q5 (pin 5)
2. 4.0MHz ceramic resonator - Q4 (pin 7)

For a grabber, I would even consider using a 4.000MHz crystal for increased stability. The resulting audio signal will fall into the range of 1kHz to 4kHz (5.x for inclusion of the DI2AM).

In this receiver, I intend to employ a 500kHz ceramic resonator as sideband filter, provided it can be slightly pulled up by a series capacitor.

600m Exciter

Finally found some time to document the exciter which I am not (yet) on air with. Oh, actually, I was on air with it, with a 1m cable attached to the output, receiving aerial 10m away; this was to see how stable the contraption is. Well, not stable enough for narrow-band QRSS, however, having seen PA3EGO's test yesterday - including some of the lessons learned on 80m - I don't think narrow-band is actually required when TXing A1A.
For regular CW the exciter should be more than enough...

The Circuit

How it works

A 4016kHz signal is generated by a gate oscillator. A second gate is used for pulse-shaping the signal. Said signal, in the next stage, is divided by 8 using a 7493 ripple counter. The 7493 counter is provided with an enable NAND (pins 2 & 3), which allows for keying without changing the load on the oscillator IC. Further the counter is configure (pins 1 and 12 connected) to operate as 4-bit counter, in this way, output "D" (pin 11) could be used to drive a subharmonic receive mixer.

In Detail

The oscillator is using a 4MHz ceramic resonator with built-in capacitors (i.e. 3 pins). It is the very standard Pierce type gate oscillator, with the only difference that the reactance is influenced by two additional components. The 39pF capacitor at the "ground pin" of the resonator is supposed to reduce the capacitance of the resonators internal capacitors.

For illustration: The internals of the ceramic resonator look somewhat like that:

Usually, the center pin is directly connected to ground. This will spare the additional capacitors for a Pierce oscillator. However, the internal capacitors are such that the resonator will the resonating at about the nominal frequency, i.e. 4MHz. As the 600m band in PA is presently assigned from 501 to 504 kHz, the oscillator needs to be oscillating in the range between 4004 and 4032kHz, hence, the capacitive load on the resonator needs to be reduced. In comes a capacitor in series to the internal ones. Experimentation revealed a capacitance of 39pF for my setup. 

OK leaving it with that, the oscillator in much to high. And in comes the variable capacitive load, which allow for smooth adjustment of the generated frequency.

The Future

The plan is to buffer the exciter with a 74HCT240 driver. Maybe the output of that would already good for local QSOs. In a further step, something that creates a little more punch will be required, maybe an IRF510...

The biggest problem to me now: How to get the RF in the aether?

Conclusion

I think this is the most minimalistic way of generating a relatively stable 600m signal, keying included... in particular with a parts count of 7 (!) - make that 10 for inclusion of a 78L05 with two blocking capacitors.

HF3 vs FRG-100

Did some longterm test of the two receivers on 600m. Well, maybe it is more the combination of gear I am comparing here, but still interesting.
During daytime, G4JNT produces a steady WSPR signal in JO22. I used this to test the following two setup:

1. FRG-100 @ Octaplumb (24.02.2010)
2. HF3 @ E-probe (26.02.2010)

Both aerials were at the exact same position for the testing periode.
It seems that the FRG-100 @ the Plumbtenna yielded an average SNR of -19dB and the HF3/E-probe combination an average SNR of -22dB.

However, there is one additional change between the two setups. At February 25th, I added a 1:1 isolation transformer to the audio cable. I am not sure if that had a great influence on the narrowband signal, it had one at the audio from the speaker.

The test invisaged for the weekend: use the HF3 in combination with the Octaplumb.

MF transverter idea

Well, there were two ideas around since I started thinking LF and MF. Transverters are certainly one way to go, although, I built a 600m-exciter by now.
The two ideas are:

1. subharmonic mixing using a 14MHz LO
2. regular mixing using a 10MHz LO

First I thought, subharmonic was the way to go, however, now, I consider the 10MHz option may be the better option.

To be honest with the dear reader, I wanted to have something built by today, however, external events drained my energy once again... So I have to be happy with the few steps I managed to do...

The transverter plan is now to run a 10MHz LO into a 4066 switching converter. Alternatively, a NE612-approach is considered. I hope, I will find my energy soon, time for the 600m experiment is ticking....

600m - Octaplumb online

The tuning/coupling-box attached with just some electrician's tape, the octaplumb does its' job on my roof deck.

600m - Octaplumb update

Eddie was pointing to a source of free ferrite toroids, hence, I took the chance and used one for the Octaplumb. The toroid came as 10:3:3-transformer. To simplify matters, I removed the two low turn count wires and kept the 10 turns winding. So much to coupling....
Resonance is obtained by the typical (see earlier entries) polyvaricon and a parallel capacitance. In this case, 680pF from another slaughtered CFL did the deal getting the loop resonating in the 600m band.
This is what it all looks alike:

600m - Plumbtenna mast

The people in my home improvement store my believe I am totally off. Day by day I drop by and buy some stuff that never will fit together in the conventional way. Example: 8pc 45deg 32mm elbows and a 2m long 40mm pipe, topped with a round furniture slider (for a VFO knob) and some lengths of loudspeaker cable. Hmmmmm ;-)

Oh well, this is what the 2m long 40mm drain pipe is for:

WARNING!

I was not sure how to react on such posts on other blogs, mentioning ME and MY design in a disparaging way like this: http://pa3abk.blogspot.com/2010/02/its-better-to-receive-tha-to-transmit.html

So, is this is what I came up with.

WARNING! 
1) Do NOT build any of my designs, they are all rubbish!
2) If you however still feel obliged to do so, build the stuff the way I designed it - if the designs still don't work, see 1).
3) Do NOT substitute any of the crucial materials, e.g. using cheap alternatives. I am trying to be as cheap as possible (ambiguity here)...

So, this is MY blog, describing MY designs that work for ME! Replace 2.5mm² heavy duty loudspeaker cable by CAT5 UTP (unshielded twisted pair) cable and you did NOT build MY design. Something else is built than. If you feel, with deviating from my design that much, still to blame me on the failure feels like an insult to me. Consequently I consider to share any future development amongst my friends only and removing this blog in its entirety.

Thank you for your understanding.

600m - The Octaplumb in the making

The success of the Plumbtenna made me buying parts for an Octaplumb.
Parts needed as follows:

• 2 × 1m 32mm waste water plumbing pipes
• 8 × 45° 32mm elbows
• 1 × 32mm T-piece

The pipes need to be cut into 8 25cm pieces. One of which will be reduced to fit the T-piece and cut in half.

Due to the 45° elbows, the Octaplumb proved to be much less painfull to fill with wire. Actually, I was able to pay attention as not to twist the twin-lead speaker cable. The octagonal shaped of the aerial increases the antenna surface area. The elbows add some length to the circumference of the loop. All in all, more speaker cable is consumed by the Octaplumb. From the 10m cable, only 25cm on one end and 97cm on the other end are left.

The Plumbtenna proved itself, however, I believe the Octaplumb will take the lead.... Easier to build, neater shape, greater aerial area. With more twin-lead used, more capacitance will be distributed at the loop, less capacitive termination will be needed.

Next step, set up tuning and coupling, apply some glue too, publish the results....

600m - Plumbtenna in use

Plumbtenna as used in the night Februray 17-18 2009

600m - Plumbtenna finished

With the evening passing by, instead of making something that produces r.f. power on 600m, I finished the outdoor frame antenna, the Plumbtenna.
Some mechanics, some basic soldering and some playing with capacitors.
I started at 680pF parallel to the tuning capacitor, resonance was a bit too high. The additional capacitor changed to 820pF resulted in a perfect resonance (503kHz) in the mid-range of the polyvaricon :-) YES!
Here is what the tuning/coupling-box looks like:

 

Funny coincidence, both capacitors I tried, came from the same dead CFL.

Oh, and BTW, I used a 6:1 toroid transformer this time...

600m outdoor loop - The Plumbtenna

Did some cutting and tweaking. This is what is done so far...

The Cutting
Both pipes are cut in half. One of the four pipes is shortened by 4.5cm, this is the approximate width the T-piece will add. Loeki loeki (please ignore the dirty floor, that's my car's room, aka garage):

The Necklace
The sequence of parts is of some importance here. The photo shows the first of the four turns completed. Still lots of slack as one can see. In the process of threading through the rest of the speaker cable, I learned that is helps to stick all pipes into all fittings and just loosen the one I want to thread the wire through. This will result in tighter turns. The cables insulation and the PVC corners create good friction :-( Some petroleum jelly could maybe help here... not willing to have that mess today, I decided to go w/o any lube. Guggsch Du hier:

The Loop
I know, the gray PVC stuff is not the best, electrically - I couldn't find any of the white stuff :-( However, the color makes this thing really look Navy/commercial/military like... OK, maybe the bar-code stickers disturb that impression a bit. Kijk maar:

Conclusions and Future Steps
It is clear that, despite my best efforts, there is still more cable in the pipe than necessary. Well, not much I can do about, should have used petroleum jelly in the first place.
Some measurements:

• one end of cable is about 60cm long
• the other end is about 50cm long
• the minimum inside side length is about 53cm, make that 55cm in average for the individual twin lead

Hence: 55cm × 4 = 2.2m and 2.2m × 4 = 8.8m. With a stretch of 10m cable available, and about 60cm + 50cm = 1.1m outside, just 10cm of cable is distributed wildly about the circumference of the loop. That should not be too bad.

I did not, but the valued reader may, take too much care that the twin-lead is not twisted. Randomly distributed turns and unmotivated twists of the twin-lead will mess with the currents and fields in the loop. Lube may help with one too :-))

Matching and coupling will be done in waterproof box.

600m outdoor loop

Bill of Material

• 10m 2×2.5m² speaker cable (€7.95)
• 2pc 1m 32mm PVC waste water plumbing pipe (€1.85/pc)
• 4pc 32mm PVC plumbing 90deg elbow (€0.75/pc)
• 1pc 32mm PVC plumbing T-piece (€1.65)

The Plan

1. The 1m pipes each will be cut in two, which will provide 4pc 50cm pipes. One of which will later be further split to accommodate the T-piece.
2. Extend the cable to full length and run it successively through the parts, i.e. T-piece - short pipe - elbow - pipe - elbow, etc. An exercise which will be repeated until all parts are dangling on the loose wire loop. Let both ends of the speaker cable some out the angled of the T-piece.
3. Plunge all parts together, carfully pulling the slack out the loop, not fully though! Check everything.
4. When satisfied, apply PVC plumbing glue to the joints and try getting the rest of slack out of the loop.

The should be some excess wire, since the measure just a bit more than 50cm for one side. The total of wire inside the contraption should thus be a little more than 8m.

Alternative Design
I bought 90deg elbows, 45deg ones are available too. Making in octagon-loop will slightly increase the aerial area, which would be a good thing! However, twice the amount of elbows would be required, resulting in severe increase of sawing/gluing work... Well, as I am a lazy dawg, I preferred as much work done as I could... therefore, a square it will be!

Further progress will be posted on the draaggolf, so, stay tuned. The project will be known as the Plumbtenna.

600m (indoor loop) WOW!

A few days of WSPR-RX on 600m.

Location: JO22da
Antenna: indoor frame 8 turns, toroid coupled
Receiver: AOR AR3030

WD2XSH/17 was received by only 11 European stations during that stretch of time :-)

Timestamp Call MHz SNR Grid Pwr km  2010-02-13 02:40   WD2XSH/17   0.503890   -22   FN42pb   10   5530   2010-02-11 19:26   G4JNT   0.503875   -7   IO90iv   0.2   406   2010-02-11 22:56   G7NKS   0.503915   -23   IO92ub   0.1   313   2010-02-12 22:40   M0BMU   0.503970   -1   IO91vr   0.002   311   2010-02-11 22:02   PA0A   0.503899   +11   JO33de   5   187   2010-02-12 18:48   PA0AM   0.503871   -3   JO11sh   0.1   94   2010-02-12 21:32   PA3FNY   0.503952   +6   JO22nc   0.5   58

600m update

Some more signals seen. No decode yet of neither G3ZJO's signal close to 503800Hz nor the one at 503880Hz. I will strive to improve, e.g. by an outdoors RX-aerial.

600m WSPR/grabber

The grabber/WSPR was running on 500kHz the better part of the last 24h. To the later afternoon, I was using the HF3, hence, the frequency offset. For the evening, I changes to the AR3030, which I adjusted to the WSPR "dial" frequency. This is, when using the SSB-filter, somewhat far off for the two beacons DI2AM and OK0EMW. Using the SSB-filter helped a big deal with my local plasma-QRM.
Now that the culprit appears to be switched off... finally... it seem time to drop the filters. As of 21:36z, the AR3030 is running with the AM-filter.

600m RX loop first RX session

First test on 500kHz, receiving DI2AM

The entire setup, loop, receiver, netbook etc. is next to my file server and the grabber computer, a very RF noisy environment. Location in the house, 1st floor of a concrete modern building in a very densely populated outskirt of The Hague.

600m RX loop

I did find some left over energy to finally build/finalize an aerial for the 600m band.

This is what I came up with....

 

This thing is about 80cm wide, uses 4 turns of 2x2.5mm² heavy duty speaker wire (a length of about 10m), resulting in 8 turns. The loop is resonated by a 2x130pF polyvaricon in parallel configuration, i.e. 260pF, parallel with a 680pF ceramic capacitor.

Have a look:

 

RF is coupled out by means of a (unknown) toroid, used as a 4:1 transformer.
This aerial resonates from 480k/c to 540k/c.
For the time being, I will spare the precious "HF-Litze" (translate: radio-frequency Litz wire) for more elaborate projects.

LW & MW SDR

Thoughts are back on 500kHz and 136kHz.
Assume we are going SDR, RX and maybe TX, one rig could serve both frequencies.

Conceptual design:

• TCXO on 4.1943MHz

500kHz:

1. 4.1943 / 2 = 2.0972
2. 2.0972 / 4 = 0.5243 (SDR center frequency)
3. about 20kHz above the band

136kHz:

1. 4.1943 / 8 = 0.5243
2. 0.5243 / 4 = 0.1311 (SDR center frequency)
3. about 6kHz below the band

In other words, the LW quadrature LO can be directly derived from either I or the Q of the SDR center frequency.

My experience is that (for my computers) 96k sampling works best. The observable ranges would therefore be:

• 476.3kHz - 572.3kHz for MW
• 83.1kHz - 179.1kHz for LW

RM80-MEPT, power measured

Terminated the MEPT with a 50Ohms 10Base2 terminator (boom boom!) and wired the whole thing up to my lab-TV.
The signal actually looked nice a clean, and was reading almost exactly 3Vpp. Some elementary maths would reveal the power being 22.5mW.

RM80 first non-local RX

It may be hard to see, my bananas made it across the channel.

 

Here is the prove.. that is what my local "control" grabber has seen:

 

Those receptions show a very weakly coupled RM80 oscillator transmitting into an indoor frame antenna. I would call that a very low-profile setup. To complete the image, power measurements will follow.

Warbler on WSPR mod

Spent some views on the Warbler's design again, and came to the conclusion that a single crystal in the either TX and RX filter would probably be OK for WSPR and AFSK-QRSS.
For RX, three crystals are foreseen, assume, we would be using one only, one xtal location could be shorted and the other unused one could be populated by a capacitive trimmer, for tuning the filter's response.
For TX, two crystals are foreseen, however, I believe a single one would do for sideband rejection... w/o any further periphery actually.
Reasons: multi-pole filters are employed to widen the filter's response... at a bandwidth of 200Hz (WSPR) of 300Hz (QRSS+WSPR) there is no reason to bother with widened bandwidth, that's what a single xtal has proven to be able in my sub-harmonic DC-RX already.

600m crystal combination

Lately, a lot of color burst crystals made it into my collection. Not sure what to do with those, I had another look at standard frequencies. And this is the outcome:

• 3.579545 - 3.072 = 0.507545

In order to arrive at our allowed range (501kHz-504kHz), the color-burst crystal would have to be pulled down by max. 7.6kHz. Tough pull, but doable.