Monday, 9 July 2018

Ouddorp antennapark


After a visit to the beach of Ouddorp I drove past a field with lots of antennas. It turned out to be a site of the Royal Dutch Navy with shortwave antennas. 
On shortwave the Navy communicates (encoded voice and data !) with its frigates and vessels. One of the antennas I recognize as a logper antenna.




Ouddorp beach:


Tuesday, 3 July 2018

Le Forty

A couple of years ago I have built Le Forty; a 40m QRP transceiver.
I received a nice picture from Carlos EA1CGK in Salamanta from his version of Le Forty ('Building in progress').

See also  http://lpistor.chez-alice.fr/forty2s.htm


Friday, 15 June 2018

Radio scale

In the days digital frequency readouts were not available, radio tuning was done while looking at the scale. Names of radio stations were present on the scale;



A nice example is the scale of a Telefunken 876WK receiver from around 1938.



Telefunken 876WK


Off topic: The island of Tiengemeten in 'het Haringvliet', about 5 km's from my QTH. The island is forbidden for cars. Only pedestrians and bicycles allowed.



Friday, 1 June 2018

Home-built TV sets


Around 1948 employees of Philips could buy DIY kits to assemble TV receivers. Two pictures of home-built TV receivers from private collections:




Friday, 4 May 2018

Digital Voltmeter

Geekcreit produces mini digital voltmeters for general purposes. Because the price of such a voltmeter is low (less than 2 euros) you can incorporate the voltmeter into each of your do-it-yourself projects.

Range is about 2.5...30 VDC and the voltmeters, to be found on aliexpress or banggood.com, are offered in various colours: red, yellow, blue, green and white.




I used one on my 144 MHz transverter:


Friday, 13 April 2018

TV test pattern

Just a nice picture of a TV test pattern from 1956. The era when black/white TV's conquered our continent:



Off topic:


Spot the frog in the pond

Friday, 2 March 2018

Friday, 9 February 2018

Discone antenna

Discone antennes cover a wide frequency range. 
MFJ has introduced a new discone antenna: the MFJ-1868.

It is designed to receive radio signals from 25 - 1300 MHz and to transmit from 50 - 1300 MHz (up till 200 Watts RF power). Interesting because it covers 6m, 4m, 2m, 70cm and the 23 cm band.

A discone antenna is omnidirectional, vertically polarized and has a rather narrow radiation pattern in the horizontal plane. This makes the antenna sensitive in the direction of the horizon. SWR remains below 1:2 for the 50...1300 MHz frequency range.

Interesting if you do not want your garden covered with lots of antennes.

The MFJ-1868 has a vertical whip affixed to the centre in order to extend the low frequency response.

Price of this antenna: appr. $70


MFJ-1868

Friday, 19 January 2018

LM3886 for lower bands

DIY audio fanatics appreciate this ‘chipamp’ a lot. See for example https://audio-creative.nl/audio-creative/diy-lm3886-chipamp/


                                 LM3886 as 65 Watt audio amplifier

It provides 65 Watts audio into 8 ohms. Audio quality is more than all right. PCB’s with this chip are available for about 10 euro’s (eBay, Aliexpress). 

Bunch of low-cost LM3886 PCB's (10 euro each)


The frequency response curve shows that we are dealing with a broadband amplifier. @ 200 kHz the attenuation is only 1.7 dB !

Frequency response


Therefore, this chip should be able to be used as an RF amplifier for the 2200 m band (135.7 – 137.8 kHz) and lower bands.

A challenge for the designer is of course to adapt the 8 ohms output to the antenna impedance.