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.