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


Friday, 19 January 2018

LM3886 for lower bands

DIY audio fanatics appreciate this ‘chipamp’ a lot. See for example

                                 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.

Sunday, 24 December 2017

Teylers museum

Some collections are special and deserve to be maintained. 

The collection of Mr. Teyler from Haarlem is such a special collection. This week we visited the Teylers museum and were able to see interesting items such as Leyden jars, 19th century light bulbs, ancient skeletons and the study room of prof. Lorentz.

More info:

Leyden jars

Oval room

Collection 19th century light bulbs

Paint art

Neanderthalers' jaw

Sunday, 10 December 2017

uBITX kit available

A DIY kit for the HF general coverage transceiver uBITX is available:

Off topic:

                                              'Waterbus', view from Zwijndrecht

Friday, 24 November 2017

73 from Banja Luka

A nice eQSL-card was found in the postbox today.
An SSB 6m QSO made August 2008 was confirmed by Vlado from Bosnia Herzegovina:

Off topic:


Wednesday, 11 October 2017

Medium Wave receiver

This is how a Japanese design of a Medium Wave receiver looks like:

And this is how it looks like as a $5 DIY kit:

Off topic:

Suriname river, Paramaribo 2018 

Saturday, 9 September 2017

Satellite TV

Today I kept track of the signal strength of the satellite TV signal from the satellite Astra 23.5 (Astra 3B transmits just above 11 GHz).

It was interesting to see that a dip in the signal strength came with the bad weather that arrived from the North Sea;

Presentation of rainfall App 'buienradar'

TV screen with sat parameters

Monday, 4 September 2017


I downloaded KiCad version 4.0.7 which is an open source Electronics Design program. With the schematic editor you can create your design without limit; there are no paywalls to unlock features. An official library for schematic symbols and a built-in schematic symbol editor are available.More info here:

The first schematic with this program:

Off topic:

Paramaribo January 12, 2018

Friday, 25 August 2017

Twin diode receiver

This radio uses two receiver chains; the supply voltage needed for the transistor amplifier is generated by a strong local broadcast station to which diode receiver number 1 (left side of the schematic) is fix-tuned. Tune with the aid of a meter and adjust for maximum detection. Low-level stations are detected with the diode receiver number two (right side of schematic). Use a germanium low signal AF type transistor (AC151, 2SB187) and Ge-diodes (AA119, AA112, AO85...). Design coil1 and 2 in such a way that Medium Wave broadcast stations are received.

A supply voltage as low as 450 mV produces audible signal amplification. Of course you have to use TWO antennas.
The designer of this radio uses for receiver number 2 (right) a loop (frame) antenna, for receiver number 1 (left) a a 20 meters outside antenna (wire). 

Receiver 1 generates a supply voltage of approx. 900 mV under load of receiver number 2.
Adjust the variable 250 kOhms resistor to approx 50 % of the voltage generated by receiver number 1 voltage (measured at + pole). Best value for 10 kOhms trim pot is 3 to 6 kOhms.

Do not use electrolytic capacitors for the 0.1 uF capacitors. Do not forget to install the 1 nF capacitor. Attention for the polarity of the diode (AA112, AO85, AA119...) in receiver nr 1.


Off topic:

Canal in Den Haag (Zuidwal / Dunne Bierkade), 7 Sep.  2017