31 March, 2015

Low power longwave transmitter experiment

Many places in the world, low power transmitters in the medium wave band are allowed. I am talking about regulations like in the US where FCC part 15 allows up to 100 mW input.

In Norway we have a particular permission for members of the Norwegian Radio Historic Society to transmit up to 500 mW on 216 kHz in the longwave band. I'm not sure if this is output or input power [it's output power]. The permission is meant to cover a personal collection of historic radios. The frequency is the one used by the main transmitter north of Oslo from 1954-1995 running 200 kW. The frequency is still allocated to Norway, so I guess that is why we may use it this way.

I grew up close to this transmitter and have fond memories of my first homemade crystal set receiving this station.

There are several low power transmitters around that can be purchased, but most of them only cover the medium wave band and not longwave (153-279 kHz). Further they are quite complicated as the frequency necessarily has to be user settable.

I looked for a simpler way to make a single-frequency transmitter and found that the function generator chip XR-2206 which I happened to have in my junk box could both generate this frequency and do the amplitude modulation. The RC-oscillator seems to be stable enough for this low frequency although I haven't tested this much.

Here are the first results with images of the circuit on a Veroboard and the oscilloscope picture of the modulation with my Tandberg TP41 70's radio on top of it listening to Dire Straits from Spotify streaming over longwave.

The circuit has very little output power, lacks antenna tuning and harmonic filtering, so there is room for improvement, but at least it works.

Too bad that the XR-2206 is obsolete and not recommended for new development!

09 February, 2015

Finally got my Ultrafire WF-501B as I wanted it

As I wrote in my blog post a few days ago, I got the intensity down for night vision for my red flashlight. But I wasn't quite happy with the level and wanted to reduce it even more. To do that I had to unsolder 6 of the 8 AMC7135 350 mA constant current ICs on the PCB of the AMC7135*8 2800mA 4-Group 5-Mode Circuit Board.

These constant current chips are all run in parallel with the VDD input for control. The 8-pin Atmel ATtiny13A chip controls all VDD inputs in parallel from its pin 6. When the VDD pin is low there will be no light. I haven't measured this, but I am assuming that this pin is pulsed in order to reduce current down from the maximum.

My measurements for the High, Medium, and Low settings are:

04 February, 2015

Dimming my Ultrafire WF-501B

I got this red LED flashlight as a Christmas present. But unfortunately the intensity was way too high for what I intended to use it for. A soft red light preserves your night vision, and is ideal for use with a telescope in the dark as was my intention. But if the intensity was as high as before the modification, night vision would suffer anyway.

I then found this YouTube video describing how the controller circuit board could be replaced by one with more functions. As recommended I therefore ordered an AMC7135*8 2800mA 4-Group 5-Mode Circuit Board with 8 AMC7135 current regulators in parallel. The image shows the original circuit board as connected before the modification in the front in the image and the new one behind it.

The new board gave me the choice of one of 4-groups:
  1. 3-mode: Lo (5%) - Hi (100%) - Strobe
  2. 3-mode: Lo (5%) - Mid (30%) - Hi (100%)
  3. 2-mode: Lo (10%) - Hi (100%)
  4. 5-mode: Lo (5%) - Mid (30%) - Hi (100%) - Strobe - SOS

30 January, 2015

- Hardly any young people are becoming hams anymore

This is what Ed Muns, W0YK, said in an interview the other day, and goes on with "because they see this as kind of old school stuff."

A year ago the ARRL web site said: "Amateur Radio showing steady growth in the US". AH0A's website with statistics over the US ham population backs this up with the curve shown here. Even in my local club we are now seeing young people signing up for licence classes. 



How different perspectives! How has an old radio amateur like W0YK come to believe in the myth of declining numbers of hams?

27 January, 2015

0.2 Watts to South Africa

This is a new one for me: Norway-South Africa on 30 m WSPR in the middle of the night. Again I am amazed at what this mode can accomplish, and also what my little Ultimate 3 kit is able to do. 

The antenna used on my side was my trusty old 80 m long horizontal loop fed with a 4:1 balun and no tuning beyond that (SWR 7:1). Output power was from a single stage BS170 driven at 5 Volts, or about 200 mW in a 50 ohms load. In this particular antenna, the output is most likely much lower. 

ZS6KN is the only non-European station who has heard me this night on 30 m, with a marginal SNR of -27 dB.


24 December, 2014

Getting ready for 60 meter

I have never had any contacts on the 5 MHz or the 60 meter band. But I guess it's time for that now.

Both my K2 and my K3 support it and about 40 countries now have access to this band according to K1ZZ in his column "It seems to us" in this month's QST.

As a first test I ran my 0.2 W Ultimate 3 GPS-controlled WSPR transmitter over night and the image shows the result. I am using an 80 m long loop skywire antenna (horizontal loop) tuned to 60 m.

The results were encouraging with the best DX being UR5VIB in Ukraine at a distance of 1887 km. By the way, considering that it is 1093 km to LA9JO in the north of Norway, one sees the distortion in the map projection used for the Google map.

I have also operated the antenna as a vertical (about 8 meters) with top-hat loading by tying both feed-line conductors together and feeding it against a ground plane. The result is quite similar. The article by Dave Fischer, W0MHS called "The Loop Skywire" in QST November 1985 is the reference for both uses of the loop. The article starts out with this catchy phrase: Looking for an all-band HF antenna that is easy to construct, costs nearly nothing and works great DX? Try this one! This matches my experience exactly as this antenna has been instrumental for my 8 band DXCC.

14 December, 2014

Waiting for an AP510/AVRT5 APRS tracker

I just ordered an AP510/AVRT5 APRS tracker and am anxious to get my hands on it to try it out. I like the small size and the fact that it is self contained - no external wires are needed to have a fully functional tracker for the automatic packet reporting system APRS: But is it useful or just a toy?

The specifications from the Amazon.co.uk site are (adapted from Chinglish):
  • SainSonic AVRT5 APRS Tracker VHF with GPS/Bluetooth/Thermometer/TF Card, Support of APRSdroid
  • GPS module: SIRF3 module, high sensitivity, fast positioning, stable power.
  • GPS antenna: 18mm x 18mm active GPS antenna, built-in LNA amplification, Star Search, locate quickly.
  • VHF Module (1W): The latest 1W VHF transceiver modules, small size, high stability for all types of wireless data transmission.
  • VHF antennas are individually matched to transmitter to ensure that the standing wave ratio is proper and the emission is efficient.
I also signed up for the Yahoo group AP510 AVRT5 APRS.

What attracted me were the reviews given by DK7XEDJ7OO (German), and APRS.facile.fr (French) and the descriptions at Radioddity and Sparky's blog,

It is evident that the 2. harmonic suppression leaves something to be desired, that the antenna is inefficient, that the programming interface isn't the easiest to deal with, and that it can be hard to set the frequency for people in countries such as Norway with PC's set for "," rather than "." as the decimal point. Hopefully I can figure out ways to deal with all these and also other issues that may show up.

12 December, 2014

Congratulations to Logbook of the World

Congratulations to the ARRL Logbook of the World (LOTW) which just reached 100 million confirmed contacts. This is the same as an impressive 200 million QSL cards out of about 630 million uploaded contacts on LOTW.

LOTW was established way back in 2003. This was only 2 years after I got my license. Since I have never enjoyed much to fill in QSL cards I embraced LOTW very quickly. I have to say though that I will of course respond with a paper QSL for those who ask for one.

But LOTW has been my primary means of confirming contacts for a decade. My DXCC was confirmed with LOTW.

Now at the same time that LOTW is celebrating 100 millions confirmations, I am celebrating 8 bands with 100 or more contacts all confirmed via Logbook of the World. This is on all bands from 3.5 to 28 MHz and has been my goal for many years. The last confirmation came from the TC0A contest station in Turkey on 80 m after last month's CQ World Wide CW contest.

I consider myself lucky to have reached 100 confirmations even on the elusive 12 m band which we all know will shut down soon not to reopen again until the next solar maximum in about 11 years time.

But as the saying goes "The journey is the reward", so what to do next as a radio amateur?