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