Looks like ...

... Italy will get again a 70 MHz (4m) allocation in 2010.

I need to build an antenna again! And maybe a power amplifier for my 100mW CW TX.

Stay tuned!

XTAL choice for 455-12 DRM converter

14060 kHz / 32 sounded good.

So does 7030 / 16.

How about 7040 / 16 then?! It gives 440 kHz, that is even closer to the I.F. of 455 kHz.

I should add this feature to my xtalfind.pl utility.

I also tried out the receiver and with my finger as antenna a DRM transmission was clearly audible on 9.8 MHz band. So I'll proceed with this IF downconverter project.

XTAL L.O. for DRM 455-12 converter

The idea of a free-running LC oscillator for my 455-12 DRM converter kept me worried for a few days. With the help of a calculator I found out that:

14060 kHz / 32 = 439.375 kHz

and

455 - 439.375 = 15.626 kHz

So, with a binary counter/divider I can get a LO acceptably close to 12 kHz. I know that DReaM software will decode a DRM signal centered at 15.6 kHz.

Where did I store that 74HC4060 ... ?!

I QRP Bullettin Spring 2010

It's finally out. The Spring 2010 issue of the I QRP bulletin. This edition is all in Italian language and I contributed with two articles. The former should appear on SPRAT too, while the latter is a World premiere, instead!

Download it here.

Please note. Article submissions are welcome for future editions of the bulletin. Even if not in Italian language, they can be translated by some native speaker.

A modification to obtain a DRM receiver?

Back to an old friend, DRM (Digital Radio Mondiale) ?! Perhaps.

I have been given a working Roadstar TRA-220, which includes few short wave bands in AM. With PLL tuning at 5 kHz steps it is not suitable for SSB/CW reception, but it can be adapted for DRM. Moreover that radio has always suffered from some design mistakes, like:

• volume control slider too sensitive
• audio volume too loud
• strong hum on audio
• loss of presets and clock unless 2xAA cells are fitted in

The radio has plenty of room inside and all components are through-hole. At a first glance the probable cause of hum is evident: 15VAC and audio line to speaker run together to/from the main board.

I have to build a (circa) 455 kHz to 12 kHz downconverter.

The IF system chip is BA4237L; the AM IF filter is marked SFU450B (thus 10 kHz BW at 450 kHz). First decision to be taken: should I pick the IF before or after the filter?

If I pick it after the filter I need a L.O. at + or - 12 kHz, so 462 or 438 kHz: how to make a stable one? (I will use my xtalfind tool to see if any of my surplus XTALs fall close to those values)

If I pick it before the filter I can make a stable 455 kHz L.O. and retune the receiver L.O. so that the resulting difference is 12 kHz. Would the incoming signal be too wide?

Let experiments begin!

Geko 201 and date bug

Yesterday I could make an excursion to the mountains and took along my Garmin Geko 201 GPS receiver. It fixed to satellites very fast but ... it showed a wrong date!

It was probably caused by a detail of the GPS protocol information, where it carries a "week" information with 1024 possible values. That's almost 20 years. See the wikipedia page about GPS for further info.

Garmin has released a firmware update (currently v2.90 for the Geko 201) that corrects the issue.

WSPR on 2m, IC706 drift and aircraft scatter

A single WSPR experiment has lead to interesting observations:

• the IC706MKiiG "as-is" is not suitable for weak signal work on VHF and UHF
  
• aircraft scatter is easily observed at 2m too
  

The picture shows both the IC706 drift during a two-minute WSPR transmission and aircraft scatter on two airplanes (at circa 2 minutes interval, their "usual" distance on the same path).


The enormous drift was present at each transmission slot (1:4 ratio), rendering unuseful the WSPR signal. This was on 2m. A compressed drift amount was later observed on 10m as well, but the signal could be decoded correctly.

Another IC706 problem, not shown in the screenshot, was the misalignment of the device and probably some difference on TX/RX frequency too: the IC706 station had to retune 400 Hz higher to appear into my WSPR receiver window.

It's always good to know your transceiver peculiarities!

FT817 external display - preview video

As announced two days ago, the external display for FT817 lives! Here is a preview video of what it does at the present time.

The microcontroller board is exactly the one of my FT817 keypad. I only needed to add a connector to source +5V and GND to power the display.




Depending on firmware size, some single-function buttons could be added around the display, such as VFO A/B, split, mode roll.

Comments welcome.