(modified) PA0RDT-Mini-Whip

The "Target HF3/W", which is supposed to service me on the boat, offers switchable 12V supply via the antenna socket. Very nice, now for some active antenna to actually make use of the possibility.

Some research on the internet brought up a design by PA0RDT (pls search for it yourself). He call's the thing "mini whip". Some would call it an EH-antenne (haha, got you there), some others would call it an amplified E-probe. The latter it actually is. It is a capacitor probing the E-component of an RF-field.

However the design may be called, is it any good?

First to mention, there are many positive reports on this device. I had my doubts, but never the less, on a yacht, aerials are a compromise whatever one does. Thus, in particular inspired by the positive feedback found, I decided to give it a chance.

The key to the amplifier-circuit seems to be the 1MOhm resistor input network. I figure, 10MOhms would propably do a better job. However, not having 10MOhms-resistor in my stock, I went for 1MOhms. Which reduced my stock that much, that the next thing I'll do will be visiting my electronica-boer in order to buy said resistors.

Here comes the modification, unvoluntary, sort of... even though a 2N5109 seems widely available, it was not in my stock... I decided to replace it with a 2N918; this required to change the emitter-resistor to something higher-ohmic, in order to reduce Ic. I went for a conservative 470 Ohms. As for the DC-separating inductor, I went for what I found (whatever it was).

And this is, what I ended up with:

The result was pretty nice, although I tested indoors only. I am curious what this probe could do, when "flying" meters above my house's roof...

Should I ever build another one, that's what I would change:

• use a 2N5109 (will propably give better results... or not)
• increase the "ground-plane" part of the probe by reducing the "12V-part"

Conclusion: The probe will have to prove itself, when hoist to the top of my ship's mast. Presently it appears to be a nice alternative to something more vulnerable, since, rugged it is!

Dutch pirates too...

Some minutes later, some Dutch pirates QSOed on 3490kHz, on top of a QSO in Arabic(?)... much stronger, no wonder, I am living in the Netherlands...

A few minutes later, this was received on 3490kHz....

To me that reads like: KKB QSY 666 HI

Hmmm, interesting, them pirates know some code... hmmmm

French pirate-stations

Caught this with the SDR:

LSB signals in French language on 3460kHz and 3490kHz. Personally, I was not interested enough to follow the conversation... It's however nice to see, that voice is readable...

CW-skimmer

Works nicely with the FA-SDR. Choose the settigs for the Soft-Rock.

more on SDR

Weekend, contest time, and so they do on 80m. Ideal to have the new setup hooked on the GPA50.

There are still faint traces of the soundcard's birdies... a prominant role they do not play anymore...

Screenshots of the action... in Rocky, the CW-click filter is activated, thus, we get nice traces of even normal speed CW.

SDR update

Some playing with programs and parameters reveiled the first results. Test were perfomed on my EeeTop (Atom N270, builtin soundcard). The soundcard creates birdies however. The image below show's a screen-catpure of Winradio with the receiver connected to the soundcard, but not the any mains supply.

1) Winradio by I2PHD works well. best results were obtained by setting the sample-rate to 96000. With an antenna connected, but by far to early in May (15:xx UTC) for the band to be open.

2) Rocky offers less features, seems however a nice choice for just listening into the band. Rocky offers two different screen setups. It's a very intuitive...

First capture shows Rocky in spectrum mode.

The second capture shows Rocky in waterfall mode.

3) SpectrumLab is very complex again. It's propably usefull to setup a grabber, for use as a receiver, it's a bit too complicated.

No other software was under scrutiny yet. As soon as there are signals on the band, I will continue testing, also publish some of my experiences in this very place.

SDR

Cool thing, sort of.... I am just about to explore the possibilities. Stands and falls with (the available) software. Personally, I will be to lazy to write anything myself. Thus, let check out what has been done before, and if it's any good to use.

First glance was promising however!

(SDR-Kit provided by "Funkamateur", box73.de, coming with a CD containing some free SDR-software).

Pierce Crystal Oscillator

Stupid me! I should have known.... After some RTFL (literature) the mystery about my 74HC86 oscillator seems to be solved. The high frequency is not due to the inner values of the XOR-gates, it is actually caused by the chosen oscillator type "Pierce". In the literature it reads that a Pierce crystal oscillator does oscillate above the crystals series resonant frequency. There we go... I should/could have known that one....

The LO for the PSKmail-TRX

First steps first... investigate if I can reach 10148kHz using standard crystals.

The idea, as shown in an earlier post, is, to use a 6144kHz LO and and I.F. of 4000kHz. This short of 4kHz. A lot, one may think.

However, when building my 30m-MEPT, I experienced that oscillators based on 74HC86 generate a frequency much higher than the crystal's nominal. Using a 5068.8kHz XTAL, I thought I was way to low, but then, I had hours of experimentation, before I got the frequency down into the qrss-band.

Thus, today, the idea was, if I can repeat this with 6144kHz crystals to close the 4kHz gap.

Well, the gap is closed, by far exceeding my expectations. The 6144kHz crystal produced a 6154kHz signal. Yes, 10kHz above the nominal frequency. Further experiments revealed, an inductor of 15µH and a capacitor with 47pF both in series with the crystal, brought the frequency down to 6146kHz. Close, but still more room for improvement appeared. The photograph shows the LO with the experimental capacitor (the long legged blue thing).

Two more gates of the 74HC86 will be used to generate an in-phase and an out-off-phase LO signal for use in a 74HC4066-mixer.

The remaining fourth XOR-gate will become the 4000kHz BFO.

Rainscatter

Just had my first rainscatter-QSO on 3cm in years. Actually, I was more prepared of testing only, in preparation of tomorrows electric storms over Germany.

Quick and dirty setup, transverter/dish behind my topfloor window (double pane, insulation and stuff). PI7EHG came in loud and strong, 55s, I figure.

Just for the fun of it, also testing the transmit-train, I called CQ; it caught me by surprise as after the first "pse k", Uffe (PA5DD) called me. QSO-time, kneeling on the floor in the most awkward position to key... no pen, no paper, no clock... as indicated, I was totally unprepared (sorry Uffe).

It also has been a surprise, that in fact the transverter still works after last use about six years ago, and even more or less on frequency.

Rainscatter saison 2009, here we come!