Jun 22, 2008

HB0- summer 2008 preparation; IC746 Mods

The Icom IC746 which we will use on 50Mhz during our trip to Liechtenstein (HB0) next july, needs some work:
  • Cleanup
  • IC151 modification
  • Master LO modification
  • Re-alignment

Cleanup
Yeah sure, but let's wait untill we return from our HB0 trip. If you can find the dials and read the screen you can make qso's right? Its a bit dusty, nothing to worry about now.

IC151 Modification
The IC-746 suffers from potential thermal failure of IC151 resulting in no RF output. During normal operation this ic dissipates some 250mW continuously, where it is rated at 330mW maximum @25deg C. Its tiny legs become the heatsink in practise.
See the small MMIC red marked in the lower left side.
5 pins (3 left and 2 on the right) are GND connections.

Just Google on IC151 and you will find many ways to rework this issue.
I found a small thin piece of copper which served as an internal cabinet ground contact of some other rig. After a small modification and carefull cleaning it was ready for its new job; act as a heatsink.
I resoldered all pins of IC151 and carefully soldered the copper plate to the 3 GND pins, making sure its flat bottom was seated against the cleaned topside.
At this moment I'm testing the rig and it works fine. After some 10min now I can feel that this copper plate gets warm, that means it acts as a heatsink. One job done.

The small solder 'flag' was removed after the picture.


Master LO Modification
The reference Oscillator has its crystal mounted in the middle of an open (!) metal cabinet.
Any quick temperature change (like during TX, when the large internal fan accellarates) will potentially result in a short-term frequency offset. Sure any (optional) TCXO will handle that, but there is a cheaper solution. Just stuff it with wadding from a first-aid kit. That is all.


Next......?
Alignment can better be done when more time is available and the rig & measuring equipment are warmed up properly.


Jun 12, 2008

HB0- summer 2008 preparation; Packet Link Setup

Preparations for another summer trip to Liechtenstein (HB0) are runnning fine.

One of the things missing at our mountain top location on the "Sareiser Joch" in Malbun(www.sareis.li), is an internet connection. Disturbing how quickly you get used to that common luxury when it is not availably for a change. A Long, (very) long time ago we started with pen & paper log but got quickly spoiled by the DX option in N1MM logging program :)

In the past our group (HB0/PI4TUE) has always succesfully used a packet link, which provided dx cluster info and, entry to relevant convers chat channels. Unfortunately our packet-node mini laptop (toshiba Libretto) from Gert, PG5D died 2 yrs ago. We were desperately in need for a new setup.
Personally I very much dislike anything related to soft/hardware programming. But one great advantage in group dynamics is that there's always someone who does like this stuff and will go to the bottom to get such working.

What is needed for our local packet node setup?
  • Short 430 MHz Yagi Antenna
  • TRX with 9K6 capability (Kenwood TMD700)
  • Laptop with AX25 Packet Node on Debian Linux OS
  • Wifi Router/USB-Hub Philips



How to build your quick & dirty 430Mhz Short Yagi
Cannabalize an old UHF TV antenna and re-use its boom and mounting bracket.
Find some alumn pieces and cut them to the required lengths according a 9el design on DK7ZB's website. Next, cut some trespa pieces and 'pop' them together with the elements to the boom. Now use any water resistant(Class: IP65) wiring box from an electronics store for the dipole. The balun/impedeande transformer is made from 2 pieces 0.25 wavelength 75 Ohm coax.
All done in a saturdays afternoon. Can't be more simple than that, now can it?



The mast is a fibre type. At only 4mtrs height in the middle of a small village, it receives the packet provider PI1EHV on 430.925 at 22kms distance, loud enough for a probeabely solid AX25 connection.


Test setup
We're up and running! Nice to "hear" that vintage 9K6 noise data connection on the 70cm TRX again.
Compliments to Rens, PA3FGA who spent 3 weeks building & programming the whole setup including the antenna.



The dx-cluster runs on the above old laptop packet node on the left. From N1MM on the wirelless connected client laptop on the right, we can setup a packet link within seconds. Three different laptops have been tested simultaneously and work perfect.
I'm getting in that dx-pedition mood again :)


What is next?
  • Build a time server so all N1MM client laptops run the same system logging time
  • Rebuild the 5el 50Mhz DK7ZB yagi
  • Build a new 50MHZ long boom yagi ??
  • Rebuild and test the old K9AY
  • re-align the IC746 and do the IC151 mod
  • etc..etc..

Jun 10, 2008

Nostalgia; Radio & TV Broadcast Antennas

Current summer weather does not allow for weekend HAM projects. Being that ”radio-nerd” doesn’t mean I do not actively enjoy sunshine and outdoors activities like sports. In fact I do and I care less about the missed opportunity to HK and JY on 6m these last few days (new ones so, do I really???).

Anyway, while swimming in B├╝ckeburg (Germany) I noticed a typical classic german Radio& Television tower in the background. This kind of view brings back early memories of our summer holiday car travel to Switzerland, Italy or Austria, during which I spotted many of those Radio/TV towers along the german highway (Autobahn).



During the trip home we passed this one more closely while taking an alternative route(B65) to the Autobahn (A2). This Radio&TV tower is situated on top of the Jakobsberg near the city of Porta Westfalica. More detailed info on the geographical site and the tower can be found on:

http://de.wikipedia.org/wiki/Fernmeldeturm_Jakobsberg#Neuer_Fernmeldeturm


According this website: http://www.senderfotos.de/nrw.htm , the site is open for public. This 135m high tower can be visited at the first level (25mtrs). The two large surroundings are at 50 and 58m height.

Before the closing down analogue TV it served:
ZDF UHF ch 26/300KW
WDR UHF ch57/330KW
NDR UHF ch54/20KW
These analogue transmitters have been shutdown since may 2006, from which DVBT was started.

Today the tower serves:
95.7MHz FM "Radio westfalica"
WDR-Bouquet 1 UHF ch26/5KW
WDR-Bouquest 2 Bielefeld UHF ch31/5KW
ZDFmobil-Bouquet UHF ch33/5KW