Friday, May 27, 2011

SWL PSK-20 for JT65 & WSPR

PSK31 is fun, agreed, however, would there be an additional option for using the PSK-20 transceiver for other weak signal modes? The question is, would it be possible to modify the PSK-20 such that instead of operating in LSB on 14.071MHz, it would also be operating USB on 14.0775MHz (corresponding to a "dial frequency" of 14.076MHz)?

Lets have a look at the PSK-20's design. We are dealing with a 9.000MHz i.f., with a 9.002MHz b.f.o. obviously. The l.o. operates at 5.070MHz. Both oscillators use crystals, a pulled up 9MHz one and a pulled up 5.0688MHz one.

Looking what could be done for the LSB to USB modification, I figure the 9MHz xtal could either pulled down by means of inductors, "penned" down or it can be replaced with another one.
Replacement would be provided by two different options. Since 9MHz is a very popular i.f., side-band crystals are available for not too much money. The second option possibly already sits waiting in the junk-box somewhere. The CB channel 3 transmit (overtone) crystal has got a nominal frequency of 26.985MHz. On the fundamental that would result in a 8.995MHz beat frequency. Still somewhat too low.... but.... in the original design, the 9MHz crystal is pulled up, remember? The CB crystal would therefore fit perfectly! Lets just assume the b.f.o. would be at 8.9985MHz.
Penning the crystal in place down, I would do "in situ". That way, everything will be set when the desired frequency is reached and only the crystal's housing would have to be soldered in place again.

Now lets have a look at the local oscillator. The JT65 centre frequency is 14.0775MHz. With an i.f. of 9.000MHz, this would be reached by a l.o. at 5.0775MHz obviously. Equally you could add up the b.f.o. and l.o. frequencies to end up at the "dial frequency". 5.0775MHz looks a an ambitious 8.7kHz up-wards pull for a 5.0688MHz crystal, and most likely it will be in the existing discrete oscillator.
 However, all is not lost. Seen that 2x5.0775 results in 10.155, there would be a couple of great options for (pulled!) digital gate oscillators and Flip-Flop dividers, namely CB synthesizer crystals.
  • 10.160 / 2 = 5.080 for JT65a: 5kHz downwards pull on 10MHz
  • 10.140 / 2 = 5.070 for PSK31: 2kHz upwards pull on 10MHz
Such digital stuff is very rich on harmonics. This is something rather annoying. However, there is a crystal ("Y4") built in the rig already. It is serving as an oscillator... ok... but... with removing the jumper "L4", and bridging (removing) the oscillator circuitry, the attenuated and Flip-Flopped digital oscillator signal can be fed into the crystal, which then will serve as a harmonics filter.

Alternatively, the 10.160MHz xtal could be "penned" down to 10.155MHz; equally, a 10.150MHz xtal could be penned down to 10.142MHz to allow for the 20m PSK31 frequency.

In this way, I hope I can create a decent dual frequency narrow-band data transceiver.

Tuesday, May 24, 2011

Look What I Found!

A local hardware store offered those:


F Type Connector to Bayonet Nay Connector adaptor. Those essentially conclude my usage of overpriced 50Ohms stuff for QRP applications.
Well, the adaptors did not came cheap, they are €2.40/pc, but I feel they are totally worth it.

Monday, May 23, 2011

QRSS Studies - the Results

Seen that there is no more for me to investigate in QRSS, other radio topics will soon become more relevant to me, and also to this blog.

The results I can report on QRSS
  • You can operate a decent visual grabber in very densely populated regions. One will see the neighbours' TV sets, which in many cases is not more than just annoying.
  • The reception of WSPR is not affected by urban noise, low profile and even indoor antennas give good results.
  • There is no need to occupy your expensive main rig or a professional receiver, a cheap and cheerful home fixed frequency RX does the jobs.
  • Setting up an online grabber is something that anyone with internet access can do, no excuses here. The demands on the respective computer are minimal. An Intel ATOM can easily operate two grabbers and WSPR (rx in my case), have a third instance of speclab running, be a print and file server and operate winamp for internet radio... all at once.

Conclusion I learned from my experiments, on-air and off-air
  • There are many more transmitting stations than receiving ones.
  • Despite my efforts to motivate the installation of additional grabbers, there are still only a few.
  • Operating a grabber blocks other activities, at least on the bands the grabbers are active on.

What I miss in QRSS is interaction, consequently, I will for the time being cease QRSS activity until further notice.

My focus for the time to come will be on data modes such as PSK500, ALE, etc.
Another thing that crossed my mind occasionally, going QRO with some homebrew kit. Saying QRO, I mean QRO, i.e. legal limit. It is not so much the urge of being heard, it's more the design challenge here.

Thursday, May 19, 2011

Froyo & Market on the A7ht

Someone hacked it, the Archos 7 home tablet. What a pleasure to see froyo and google market running on the gadget. At times it seems to struggle during bootup, this could be due to the lack of cell-network hardware.
With expanded options of market, the cheap tablet is really useful to me now. Let ne give you an example, there are apps out there for watching webcams... perfect to keep an eye on one or more grabbers...
Froyo is not slowing down the device, this was the first thing I feared. What  like about froyo in particular, the orientation of the plain desktop changes with rotation of the device. Occasionally is comes really handy.
Now looking for some interesting ham-radio apps...

Monday, May 16, 2011

The Ultimate Icom IC-M700D+

OK, this may sound a little unfair and overdone... today I managed to secure an Icom IC-M700 purchase. That means, I will create the ultimate IC-M700(whatever)+++.
Here is the idea: All of the IC-M700xx brought their individual pros and cons. The aim is to create the ultimate transceiver based on whatever Icom had to offer in the M700 series.
I believe, I have found it!

  • IC-M700D: three power regimes, USB only (limited TX-QRGs, see mod)
  • IC-M700: USB/LSB, TCXO, one power regime only
  • the modified IC-M700D will be equiped with the RF-unit of the IC-M700 and hence providing USB and LSB voice operations at three different power levels, which to me sounds like a nice rag chew transceiver.
  • the IC-M700 seems to be crippled by the use of the USB-only RF unit of the IC-M700D. However, the base band stability of the TCXO makes the USB-only unit a perfect transceiver for digital modes.
Still there is this perfect all in one box sitting in my shack, the IC-M700TY.
However, since it is very hard to get your hands on one of those, merging the IC-M700D(or F) with  an IC-M700, will get you at least half the way to an IC-700TY.