Thursday, December 31, 2009

Sangean ATS 909 (first impressions)

Bought myself a new receiver for Christmas. Yes, yet another one. Here's some blabla about my first impressions.

For €199.- the package contains, the receiver (oh well...), some earphones and a 110/230V power supply with an adapter for American sockets. OK, and a very short manual.

When first attempting to engage... nothing... ???? Ahhh, by factory default, the keys are locked. That was a surprise, honestly.

There are a couple of features not really standard to such receivers. One is RDS which can be used to automatically program the internal clock. Interestingly enough, the clock can be set to two time zones and daylight saving time can be toggled by a single key. Speaking of "FM", the tuning range is 76 to 108MHz. There are two memory pages for FM, which can be programmed automatically (aka. ATS) by a single key.

The ATS also can be used for medium wave and long wave. The feature scans the respective band and stores the strongest stations to memory channels.

The MW channel spacing can be selected to 9kHz or 10kHz at a well accessible switch on the right side panel. This side panel also carries switches for "auto time set", "tone" (news/normal/music) and AM bandwidth next to a potentiometer for volume and a rotary tuning encoder.
The left side panel houses connection for DC, headphones, line-out, record trigger and external antenna. Also to be found, a potentiometer for RF gain (nice touch!).

Now to the more interesting things, short wave and first impressions as a grabber receiver.
Frequencies can be selected in a couple of ways, hacking it in by using the key pad, up and down tuning keys (5kHz steps) or the rotary encoder on the right side panel. The steps of the encoder can be toggled between 1kHz/40Hz in SSB mode and 5kHz/1Khz in AM mode, a third position disables the encoder. Since fine tuning in USB/LSB is 40Hz, there is no need for a clarifier, which therefore is not present.
When tuning, the receiver mutes whenever the frequency changes by 1kHz, even when using 40Hz steps. Within the kHz, the receiver does not mute. Seems some PLL locking.

One interesting feature is the memory system. Whenever a frequency is typed in which is stored in somewhere, the memory system changes to the memory page which the frequency is stored in. The mode is change to the stored mode.

During the first night, the receiver was very unstable and drifted a lot, the QRSS test was very difficult, doubts raised on the usability of the receiver for QRSS. The major drift was in one direction only and slowed down with time. That made me believe that this drift was due to fresh components which were not aged. The second attempt was going much better, the gadget was left one for the best part of the day. Before the test, I switched it off for a couple of hours, to see the effects of the warming up. Stability is much better now than it was during the first test.

BTW, for QRSS the RF-gain feature proved itself as very useful.

I hope that further use will further age the frequency determining components and thereby increase the frequency stability. If that will happen, the ATS 909 will make a really nice portable grabber setup.

Sunday, December 27, 2009

Receiver for 7059900Hz

Several obvious options here.

SDR using 4x the qrg. Here, we a got crystal from Nick, 28.188MHz, resulting in an SDR center frequency of 7.047MHz. Alternatively the canned 28.322MHz-oscillators provide a center frequency of 7.0805MHz.

SDR using half the receive frequency, phase shifting of 90 degrees done by an RC circuit. A crystal is available: 3.535MHz (from Rich). This results in an SDR center frequency of 7.070MHz.

And finally, there is a crystal available, from, having a frequency of 3.530MHz. This is too close for SDR, but allow for a subharmonic direct conversion receiver, more or less in the same way as I use it for 30m. The only drawback here, there is not 7.060MHz crystal yet, hence, no easy way for a sideband filter. However, there are crystals for 7.055MHz (Rich, and 7.058MHz (Rich), which could serve as a notch filter, just like in Gene Marcus 30m WSPR transceiver.

Sunday, December 20, 2009


Did some soldering today, that how far I came. OK, nearly. Check out the diagram. All is done besides the frequency modulation input with its diode (LED or rectifier) and capacitor. The amount of capacitors in the crystal network is due to experimentation, and this is what drops my oscillator from 13.999MHz to 14.006MHz with 14.001MHz in the mid tuning range of the capacitor.

Design idea here: use as much of the 74HCT240 as possible. Hence, one inverter as oscillator, three buffer (I know, this does not really make sense, but wait!) and the block of the other four gates as power amplifier, all four in parallel for use with a step-up transformer. The "PA" is equipped with an enable/disable switch.

So, here is comes, why use three buffers. Well, the first buffer is required since oscillator gate is operated in "linear mode". This first buffer inverts the signal, or in other words, phase-shifts it by 180 degrees. The second buffer inverts the signal again, providing a signal which is phase-shift by another 180 degrees, delivering an in phase signal to the oscillator. Who knows what this can be used for...
OK, now the third buffer seems really useless, but, it is not ;-) This buffer terminated the second one properly, so that always a nice signal can be drawn from either buffer 1 or buffer 2.

Sunday, December 13, 2009

Astronomy meets QRSS

Inspired by last nights experiment, I suggest the following:

Let's transmit in predefined time slots, as the IBP-beacons.

This could be used for the following procedure:
  • start a grab a some 10secs before the slot, and end it some 10sec after the slot
  • put the spectrum in a file named after the slot + sequence number
  • register and stack all files of a single slot (as it is done in modern astrophotography)
The question is, how to automatize this. I'll look into this...

Benefits, extreme noise reduction due to integration over a longer period, as done in astronomy. (check my astronomy stuff at - webcam imaging with small telescopes).

Friday, December 11, 2009

Wednesday, December 9, 2009

E-probe experiment (30m)

The Suburban Subharmonic Grabber uses a wider than 100Hz range.
Hence, occasionally a WSPR station makes it into the visual
(displayed) spectrum. When I did my E-probe test, under comparably
poor condx on 30m, RW6XC came up, low enough to nicely be seen
on the grabber spectrum. The interesting part, a visual spectrum
of a single station can be compared to the signal to noise ratio
determined by the WSPR software.

Have a look:
Date: 2009-12-09
Station monitored: RW6XC
Power (indicated): 5W
Distance: LN23AS -> JO22DA = 3059km

19:58 -20
19:46 -24
19:38 -20
19:34 -19
19:30 -15
19:26 -14
19:22 -12
19:16 -7
19:12 -8
19:08 -7
19:04 -11
19:02 -12
19:00 -19

The other part of the test was, to see if and how many
station are received by this minimal setup. Remember,
this is an E-probe feeding a homemade direct conversion

Stations received during 24h using the E-probe:

So, second experiment, yes, you can receive stuff with absolute minimal gear...

Tuesday, December 8, 2009

indoor DCTL & WSPR on 30m

This is what my tiny subharmonic d.c.-rx heard when wired to the indoors DCTL.

2009-12-08 03:36
2009-12-08 13:40
2009-12-08 14:24
2009-12-08 09:46
2009-12-08 08:54
2009-12-08 07:36
2009-12-08 07:30
2009-12-08 07:42
2009-12-08 09:44
2009-12-08 10:10
2009-12-08 09:40
2009-12-08 10:34
2009-12-08 10:34
2009-12-08 10:46

So folks, here you have it, you can receive weak signal living in a concrete building in a dens suburban environment.
In another experiment, I will use the E-probe, outside at my balcony, stay tuned for the data.

new low frequency ideas part 2 (RX)

There is another added bonus on CB crystals for low frequency operation. At least for the 136kHz band.

A CB-channel 22 TX crystal (27225kHz) would result in a frequency of 138.9kHz, just 1.1kHz off the upper band edge and 3.2kHz off the lower band edge.

Given the fact that the two last frequency divisions (see the earlier blog entry) resulting in 4 (two flipflops) it appears somewhat obvious to use just this crystal in a direct conversion SDR receiver.

new low frequency ideas (TX)

Working with dividers seem to have advantages to me, amongst: greater stability and easy digital design. The only question is, are there enough crystals in a close range?
Well, what about old CB crystals? And how would those get us onto the 136kHz band?

First things first!

Here is what I came up with and how I started the process:

There is an industrial crystal 27000kHz crystal, divide this by 196, get us to 137.76kHz, just 60Hz off the QRSS COA (center of activity).
How to divide by 196, well, that actually easier than I though:
  1. 196/2=98
  2. 98/2=49
  3. 49=7*7
The recipe is hence, two counters to 7 in series (so that they multiply) and two FlipFlops. There we go, a 50% duty cycle with a cheap crystal in the middle of the QRSS range. Drift should not be an issue here, assume, the oscillator drifts by 1kHz, that would result in a 5Hz drift on long wave.
I think, there is even a canned oscillator of that frequency, making the design in particular simple.

And now to the added bonus: CB-XTALs!

I reach in my junk-box to see what crystals I got from old CB radios. Some calculation revealed the following:

  1. 26600/196 = 135,71
  2. 26610/196 = 135,77
  3. 26620/196 = 135,82
  4. 26630/196 = 135,87
  5. 26650/196 = 135,97
  6. 26660/196 = 136,02
  7. 26670/196 = 136,07
  8. 26680/196 = 136,12
  9. 26780/196 = 136,63
  10. 27000/196 = 137,76
  11. 27005/196 = 137,78
This covers essentially the whole 136kHz band with junk crystals from CB radios. Even better, look at the channel count, to me that looks like I will be using the casing and the channel selector too ;-)
I missed a couple of frequencies, since I got no crystals for those in my junk box.

The internet discloses that there are RX crystals for the CB channels 8 to 40 ranging from 26600kHz to 26950kHz with 10kHz increments, a few channels skip however. 10kHz steps will result in 51Hz steps in the 136kHz band.
Additionally, there are TX crystals for CB radios. CB channels 1 to 4 (26965kHz to 27005kHz) would be interesting here.

One may consider to experiment with VXOs, since old CB radios have those anyway, ranging +/-5kHz, which would the cover essentially the whole band, with just a few gaps due to the lack of crystals.

The same principle could be serving for the 500kHz band. Here, one would require a division by 54, which would be two counters 9 x 3 = 27 and one flipflop => 54. CB TX crystals from upper channels could be used. Since I don't hold a licence to that band, I will not look any deeper into this. Nevertheless, I hope, that someone finds this useful.

Monday, December 7, 2009

80m results (06.12.2009)

Colin and I did some tests on 80m lately. The following spectrum shows the final minutes, before Colin QSYed. Receiver setup on my side: NASA Target HF3 + E-probe. The computer used for analysing is a Packard Bell "dot" netbook with an Intel Atom N270 processor.

The darker regions on the spectrum are due to a local (The Hague) sideband station pulling the AGC to the max. But still, there is some F1A (FSK-CW) coming through... The cheap'n easy setup still allows for detecting weak signals...

Saturday, December 5, 2009

136kHz ideas

Some considerations to generation of frequencies in the region of the long wave band using counters and cheap crystals. The first number is the resulting qrg in Hz, the second number is the crystal frequency in MHz and the third number is the divider/counter.
Additionally, there are some approaches mixing different frequencies, I will not go into this in the present note.

The trick is to end the chain of dividers with a division by two, creating a 50% duty cycle.

I would like to point your interest to some frequencies for which ceramic resonators are available. Those could be nicely pulled, given the ratios, the stability of a ceramic resonators oscillator seems OK-ish to give some results still. Assume 1kHz drift @ 5.5MHz. This would resulting in a 25Hz drift @ 136kHz, not desirable, would allow for first tests however. It is clear that care should be taken to avoid drift all together.
For crystals, one could consider moderate super-VXOs.

At the end of this message, a band plan is attached. Some frequencies I listed are actually outside the band, consider this as a hint to SDR-receivers, in particular when the last division could be by 4.

There are two candidates for QRSS marked in red. However, both require a division by 13 :-(

Simple solution "ripple counters"

  • 138550 = 4.433619 / 32 (=8x4=2x2x2x2x2)
  • 138550 = 8.867238 / 64 (=8x2x4=2x2x2x2x2x2)

One decade counter + ripple counter or flipflops
  • 136533 = 9.8304 / 72 (=9x2x2x2)
  • 137500 = 22.000 / 160 (=10x8x2)
  • 138240 = 22.1184 / 160 (=10x4x4=10x4x2x2)
  • 136533 = 4.9152 / 36 (=9x2x2)
  • 138888 = 5.000 / 36 (=9x4=9x2x2)
  • 138888 = 10.000 / 72 (=9x2x2x2)
  • 144444 = 5.200 / 36 (=9x4=9x2x2)
  • 136533 = 6.5536 / 48 (=6x2x2x2)
  • 136533 = 7.3728 / 54 (=9x3x2)
  • 136533 = 14.7456 / 108 (=9x3x2x2)
  • 136533 = 16.384 / 120 (=10x3x2x2)
  • 136550 = 2.4579 / 18 (=9x2)
  • 136533 = 24.576 / 180 (=10x9x2)
  • 136533 = 3.2768 / 24 (=6x2x2)
  • 136533 = 3.6864 / 27 (=9x3)
  • 136533 = 4.096 / 30 (=5x3x2)

Two decade counters + ripple counter or flipflops
  • 136364 = 3 / 22 (=11x2)
  • 136364 = 6.000 / 44 (=11x2x2)
  • 137675 = 3.579545 / 26 (=13x2)
  • 137675 = 14.31818 / 104 (13x2x2x2)
  • 137255 = 14.000 / 102 (=17x3x2)
  • 136364 = 15.000 / 110 (=11x5x2)
  • 136364 = 18.000 / 132 (=11x3x2x2)

Ceramic resonators
  • 137500 = 5.50 / 40 (=10x2x2)
  • 138889 = 5.00 / 36 (=9x4x2)
  • 138889 = 10.00 / 72 (=9x8x2)
  • 136389 = 4.91 / 36 (9x2x2)

Now, what to select, taking into account the band plan:
135.7 - 136.0 kHz
Station Tests and transatlantic reception window
136.0 - 137.4 kHz
137.4 - 137.6 kHz
Non-Telegraphy digital modes
137.6 - 137.8 kHz
Very slow telegraphy centred on 137.7 kHz

Grabber news: WSPR2 works

The new version of WSPR allows to set a RX BFO other than 1.5kHz. The usable range stops at 3kHz, just enough to use the subharmonic direct conversion receiver for spotting WSPR signals.

Assume the following: The mid-qrg of the WSPR band on 30m is 10140.2kHz. With a "BFO" setting of 1.5kHz, that gives the famous 10138.7kHz. The subharmonic receiver's LO runs on about 5068.8kHz (depending on the individual canned oscillator). Double that, it will give 10137.6kHz, resulting in a "BFO" frequency of 2.6kHz to reach the WSPR-band.

My resulting LO frequency is a about 69Hz further off, here comes a correction in, one has to measure first. For me, it results in a "Dial Frequency" of 10.137531MHz and a "Rx BFO" of 2669Hz.

Good news for WSPR-users, I will be now monitoring whenever the grabber is set to 30m.

Wednesday, December 2, 2009

30m DCTL as presently used for the JO22-grabber

Here come the numbers... (bonk bonk bonk!!! for the insiders):
  • radiator total length: 327cm
  • matching stub length: 46cm
For the radiator, i.e. loop, this is the actual wire cut length. Meaning, there's about 5mm vanishing into the luster terminal.
As for the stub, same story, however, the stub is shorted, and whatever is needed for that short is not taken into account by that figure. However, I believe, that this would not make a big deal difference in matching anyway...

This is, how stuff is wired up in my (experimental) setup:

The "matching stub" (current center of the loop) is connected to both terminals, either of the loop leads to the respective terminals. The whole thing is matched to RG58 by means of a 4:1 balun using a T50-6 toroid contraption (classic approach).
With this setup my MFJ-analyzer was showing a SWR of 1.2:1 @ 50Ohms. Fine with me. The loop is sensitive to its environment however.

Short note on how I resonated this loop. It was cut to a frequency much lower than wanted, since my aim was a single frequency loop for a grabber. Anyway, the 30m band is not that wide, or is it? With the analyzer engaged, I progressively cut off bits of the "voltage"-end of the loop, until I reached the aimed mid resonance frequency. This should be done symmetrically, in order to prevent noise caused by local E-fields (vacuum cleaners, hair dryers, etc.).

No toroid in the junk box? This could be an alternative to match TV-twin lead to 50Ohmx coax:

It was giving a slightly inferior result, hence, the T50-6 balun won and will stay connected with the grabber for the upcoming future.

DCTL demystified

This is an attempt to explain my understanding of the DCTL (Distributed Capacitance Twisted Loop) antenna. Personally, I am convinced to have understood its functioning. In a second blog entry I will provide detail for a 10MHz DCTL antenna, so you could build one yourself.

Let's start on a simple design of a self-resonant loop antenna. This concept is also known as frame antenna. A sort of magnetic loop without a capacitor but two windings instead. The two windings (parallel conductors) will provide a distributed capacitance which will form a parallel resonance LC-circuit, as we know it from regular magnetic loop antennae.
Let's assume, the feeding is done by a T-match, this would result in the following configuration (red=feedline):

The T-match as got two feed-points to the otherwise closed resonance LR-circuit. Those feed-points are marked in the following sketch:

Assuming that the conductor of the loop between the feed-points roughly matches the feedline's impedance (200-300Ohms), one could squeeze this section into a hairpin structure. The following sketch would reflect this...

OK, the loop is matched now, but what about the resonance? Well, if the loop is cut well, that is the end of the story! Why bother? Yes, really, this could be the end of the story if you intend to use the loop in a relatively narrow stretch of QRG.

However, here is, what was though about in 1994, the end result of the DCTL (as you may find it on the internet).
The sketch show a capacitive (open) stub which terminates the loop in a fashion known from magnetic loops. This stub adds a few pF only, and should be cut to the mid-resonance of the DCTL. The stub lowers the DCTL's frequency, hence, the DCTL has to be cut to a QRG above the aimed operation frequency. Finally, having a DCTL self-resonant, i.e. w/o capacitive stub, above a ham-band, allows for a kit of stubs to cover the whole band.

With this tiny post, I hope to focus your attention of a very portable antenna, which is almost forgotten, probably because it was never understood or decently explained in the first place.

Tuesday, December 1, 2009

bonk bonk bonk... (DCTL)

That would be the echo of me banging my head on the wall... Now that the thing is in resonance, it works brilliantly with my subharmonic direct conversion receiver. Grggrrrrrr, I took it for granted for several weeks, that the dimensions of the loop were ok, and put all efforts to the 6:1 balun... Now that I think of it more clearly (don't you ask me why this didn't happen earlier, you don't wanna know!), it is sort of clear, I am not using 300Ohms window line as I used for the 40m DCTL, but rather EUROPEAN (!!!!) TV-twin, which is 240Ohms (I believe), and thus, also has got a different capacitance per length.
Bonk bonk bonk ...
Bonk bonk bonk!!!!
But now, it seems, I am onto something. Receiving the mystery station from JN44AE now, 2037z.
The DCTL finally usable for QRSS? I hope so, I intended to use this sort of aerial for future journeys, to put signal in the air, or maybe receive occasionally...


Banging my head against the wall... stupid me!!!
The 30m DCTL, even with the new balun I produced this morning (before the O.P. @ work) did not perform. And guess what??? Now that I finally checked it out with my MFJ analyzer, it is resonant 500kHz lower, somewhere around 9.5MHz.... Yep, for a narrow-ish band antenna, this cant do the trick.... Oh man! I wonder how I received Andrew's MEPT with this thing in the first place....
Now, more cutting will be done, and I promise that I will have the aerial as successful as the big brother I once cut for 40....
Still banging my head....