My LF radio transmissions in February 2026

🔘I was particularly active transmitting on  the LF ∿136KHz/2190m long-wave 📻radio band during 📅February.  My radio transmissions on that band have now paused until I resume them later in the year when the long nights return.

My transmitter ⚡is home made to my own design. The output power is 150 watts. My🗼 antenna consists of vertical sections of aluminium tube totalling 📏14m long  to the top of which is connected a wire which extends horizontally for 📏47m. Two loading coils➿➰are also connected; one ➿at the base of the vertical section and the other ➰to the far end of the wire. Both the 🗼antenna & transmitter have been featured in several previous posts.

The modes which I predominantly used were the 32 minute ⏳beacon mode called "Opera32", and the slow morse modes known as "DFCW10" ( Dual Frequency CW with 🕑10 second dashes ) and "QRSS4" ( 🕑4 second dots ).

My transmissions were reliably received 🎧by the 📻receiving station ( 'grabber' ) of DL0AO near Amburg in Germany at a distance of 700 kilometres. The signals being received can be viewed 🔗online in near real-time, from which I made the screen-shots below. Additionally my Opera-32 signal was at various times also received in 🗺 Greece, Croatia, Norway, Russia & Sweden.

List of Opera32 detections by DL0AO

 

Opera32

DFCW10

QRSS4

I have had 2-way contacts with radio amateurs in 11 other countries on the 2190m band. Unfortunately during February 2026 my transmissions were not answered !

Low Pass Filter for the 2190m Long-Wave band

🔘It is only a small accessory. However, the purpose of the filter described here is to improve the spectral purity of the output signal from my low power RF amplifier ( 📅22.02.2013 ), for the LF 135.7-137.8KHz 2190m longwave 🗼amateur radio band, when being driven from the phasing-exciter (📅 23.01.2024 ).

The filter family is the Chebychev low-pass type, having 50 Ohm input/output impedance, and a theoretical response of 5dB passband ripple, bandwidth 160KHz, and insertion loss better than 0.3dB between 135.8KHz and 140.9KHz; essentially a single section, 3-pole, low-pass, 𝞹-filter.

Schematic diagram of the filter

The input is connected to the low power RF amplifier, and the output to the antenna 🗼via any swr/power meter. Input and output are interchangeable as the filter is symmetrical and bi-directional.

The completed filter - cover removed

I designed the ribbed ( grooved ) coil ➿former ( just visible, lower centre in the above image ) for the precise coil length, coil diameter and wire thickness required, and made it from dark-grey PETG filament on a 3D printer. Two capacitors connected in parallel are required at both the input and output terminations to obtain the correct overall value. The enclosure chosen is a two piece U-section aluminium box. I didn't remove it's outer blue protective film.

The filter was connected to the amplifier and tested at ∿ 136.130KHz, modulated with an audio 👂tone of 1400Hz ∿ by interfacing with my DdsModTerm software (📅 31.12.2024 & 27.03.2025 ). A spectral plot, ( purple: vertical - amplitude dBVrms, horizontal - frequency Hz ), of the output signal ( see image below ) was displayed on an oscilloscope.

Spectral plot (purple) of the signal at the filter output

The line 'cursor A' was placed across the top of the signal with the largest amplitude of +17.2dBV, i.e., the main carrier signal of 136.13KHz located at the centre of the display. The line 'cursor B' was placed across the top of the next largest signal of -30.4dBV; an unwanted  spurious distortion signal that has been generated at approximately 7x the carrier frequency i.e., 950KHz. The difference in amplitude of these two signals is 47.6dBV. All the other spurious signals are more than 47.6dB down on the wanted carrier. Without the filter the unwanted distortion products were much higher in level. So the filter has made a considerable improvement. I am very pleased with the result !

The yellow waveform ∿ is the output signal versus 🕠time. The amplitude is 23.4V peak to peak. This equates to an output power of just 1.4 watts. It will be interesting to see what can be achieved when transmitting at this power level regarding📻 reception distance🌐. To find out, I shall have to wait until the ❄winter when propagation conditions on the 2190m band are most favourable. 🔘

My low power LF radio signal is received in Germany

🔘 Almost 11 years 🗓 have passed since I last used my low-power transmitter power amplifier ( see 08.05.2013 ) based on the TDA2030 class AB audio 🔉 amplifier i.c. ( see 22.02.2013 ). Since then several data 💾 transmission modes, e.g., FST4W,  have become popular among radio amateurs who are active transmitting on the LF 2190m/136KHz 〰 ( longwave ) 📻 band. I also have high power transmitting equipment for that frequency band. However I wanted to conduct a simple test by transmitting a very low power beacon signal using FST4W to determine at what distance it might be received.

My setup for the test was the phasing exciter ( see 02.11.2017 ) as the signal source driving the low power amplifier. The antenna 🗼 was my usual one for the 2190m band; a 47m  long x 13.5m tall base and end-loaded inverted 'L' ( Ꞁ ) ;  see 19.02.2010 et al.  The transmit frequency ∿ was 136.13KHz, transmitter output power only 3.5 watts, ( similar to the power consumption of a small LED lamp 💡 ), and beacon transmission, consisting of my callsign, location and power level, sent at 5 minute intervals.

Equipment used for the low power test on 2190m band

I began sending beacon transmissions during the evening of  21.01.2024. Previously, during the tests on 8 May 2013, ( albeit using a different mode ), the reception distance had been only 17 kms. I was doubtful if anyone beyond that range would receive my signal. So I was very surprised, when, at 2120 utc 🕤, a reception report was posted 📮 on wspr rocks  ☁ that my beacon signal had been received 📶  near Chemnitz in Germany, at a distance of 582 kms. Incredible and amazing 😀 !

 

LF = Low Frequency.

135.7-137.8KHz ( 2190m band ) is the lowest frequency band allocated to radio amateurs.   

Dual band transmitter power amplifier for the LF ( 2190m ) and MF ( 630m ) bands

home made enclosure 25 x 24.5 x 12cm

band module for the 2190m band is shown installed

I've recently finished building another amplifier for my transmitting setup for the 2190m/136KHz and 630m/475KHz bands. It is a switching amplifier design based on Class 'E' topology, using four IRF640N  MOSFETs in parallel. To allow operation on both bands I constructed the output tuning and matching circuit for each band as a removable module; changing the frequency band of operation just requires installing the appropriate module. I have also fitted a RF voltage sensed automatic antenna changeover circuit.
In use the amplifier runs only slightly warm. Each MOSFET is mounted on a separate 4.4degC/W heat-sink, two cooling fans are running and there is ample ventilation. So my work on the thermal aspects of the design was worth the effort. By using 4 MOSFETs in parallel there is very little heat to be dissipated anyway as their combined 'on-resistance' is extremely low. Amplifier efficiency is about 83%.
I was very pleased to get a reception report of my signal on the 630m band from Bantry, south-west Ireland, ( distance 2085 kms ), as well as reports from Greece and Spain.
My future plans are to paint the front panel of the enclosure, and make a hinged top cover.
I can provide the circuit diagram on request by email.

More details of my low power transmitting setup for longwave

Since the posts on 22nd February and 8th May, I have received requests to post more information on the setup I used for my low power test transmissions on the longwave 2190m band.

The circuit schematic and pcb artwork for the AF amplifier are shown above; click on the images to expand them. The original size of the artwork is 70 x 100mm. The pcb is single-sided; top component layer, bottom copper layer. Anyone wishing to copy my pcb design might need to modify the tracks connecting T1, depending on the actual transformer which is available and the windings used.

A +18V dc power supply can be used for greater output power. I didn't try this only because I don't have a convenient way of providing that voltage, and also the fan is a 12V unit.

My very low power transmissions on longwave

Last night I made successful radio test transmissions on 137.7KHz, 2190m band, using only 3.5W transmitter power. My signal was received, ( screen capture below ), at a distance of 17Km. The signal strength suggests that 2-way communication at this power level would be possible over a much longer distance. The vertical streaks are probably static crashes as a thunder storm was active in the vicinity.

My setup was my own-design PIC controlled DDS and the TDA2030 AF amplifier featured on 22 February. 

It is unfortunate that amateur radio activity on the 2190m band is so low, as it is possible to enjoy communicating on this band with a minimal setup, as I have just shown.  

Experimental low power amplifier for 2190m longwave

I salvaged some potentially useful parts from a faulty pc power supply, e.g. bridge rectifier, schottky diodes, heatsink, fan, chokes, transformers. The 12V-0-12V, 5V-0-5V output transformer typically operates near 40KHz. I thought of using it for the output matching transformer in a low power transmit amplifier for the 136KHz, 2190m longwave band.
My design is based on the very cheap, ( half a $ ), TDA2030 class AB audio amplifier ic, which has a bandwidth of 140KHz.
The circuit is experimental. I was curious to find out if such an amplifier would be useful for 136KHz, despite using some untypical, possibly 'unsuitable', components.

I built the amplifier on a home-made printed circuit board, 70 x 100mm. The ex-pc transformer, ( yellow & black ), is on the left. The TDA2030 is mounted on the ex-pc heatsink. ( Pcb artwork and the circuit schematic are available from me on request ).

Fitting the circuit board inside the old pc power supply box, ( cover not shown ), with its original 12V fan, and adding a LED, rf and dc connectors, completed the construction.

For testing, I powered the amplifier from a +13.6Vdc power supply and connected the input to my frequency synthesiser tuned to 137.8KHz. With the input attenuation set to minimum, and the output terminated in a 50 Ohm load, the measured voltage gain was 41.75dB. Output power was 3.5W.
I could now either connect the amplifier directly to my longwave antenna and make some very low power test transmissions, or use it as an intermediate amplifier stage in a much more powerful transmitter, yet to be built.

Chirp-Hell on longwave

On 14th November 2012 I reported success with the tests on the work-bench of the improved ssb phasing exciter for my 2190m longwave transmitter. Soon after that I installed it inside the transmitter enclosure. Since then I had been waiting for an opportunity to test it using full transmitter power into my antenna in a real 'on-air' situation, with a more distant receiver. 

So early this morning at about 1.00am I carried out transmission tests with Jacek, SQ5BPF, in Warsaw. My signal was quite readable on his grabber; screen captures above. The noisy band conditions at his location are also very evident.

I was transmitting on 136.9KHz upper sideband, modulating with 800-810Hz chirp-hellschreiber audio tones. Transmission speed was either 5 or 10 secs/character; the vertical markers are 1min apart. We then completed a chirp-hell to qrss1 cross-mode contact; quite obscure, so it's probably the first time ever it has been done !

Improved phasing exciter

I have completed some improvements to the single-sideband phasing exciter, ( post 25 January 2010 ), for my longwave transmitter, just in time for use during the good propagation conditions on the 2190m band over the winter.
The passive phase shift network was not producing accurate 0 and 90 degree phase shifted AF. In fact it was well outside specification; perhaps not surprising as I bought it in 1978. So I replaced it with an active circuit based on a dual op-amp. I optimised the unwanted ( lower ) sideband suppression at 800Hz. There is little point anyway in achieving exact quadrature audio channels over the entire speech band as the modes in use on longwave are extremely narrow-band.
I added a tuned class-A post-mixer transistor amplifier stage.
Upper sideband is now selected automatically as I have disabled the sideband switching facility; until such time when I see a lower sideband signal on the band.
The top picture is my signal, received on 137.7KHz, from just the exciter sitting on the workbench, ( lower pic ), when transmitting using chirped multi-tone Hellschreiber mode. As can be seen, the signal occupies only about 5Hz of band !

Two generations

The early MKI ( lower ) and very recent MKII ( upper ) embedded control frequency synthesisers are both resting on top of my longwave transmitter. I will interface the MKII with the transmitter as that was always one of my intended applications. The MKI will now be used as an item of test equipment on the workbench to provide an lf signal source.

New antenna radiates

The new antenna for longwave, mentioned last time, radiates. I have been making some test transmissions on 137.7KHz and these transmissions have been received by Jacek, callsign SQ5BPF, on the other side of Warsaw. The screen capture below shows how he saw my signal on his 'lf grabber'. Incidentally, he could also hear it.
So now I have a reference signal with which to compare future signals as I make improvements to the antenna installation; the aim being to make the signal stronger and the signal trace white rather than the orange colour it is now. Losses in the system have to be reduced. To achieve this, I shall start by burying more copper in the garden. This will be a very labour intensive and time consuming activity. I shall probably be eaten alive by mosquitos before completion ! I hope to report total success in the near future - if I survive the ordeal.

Wire in the sky

I have erected a new antenna in readiness for the restart of my radio activity on the 136KHz 2190m longwave band during the coming autumn and winter season; simply a 45.9m long wire, and a number of bare copper conductors buried in the ground directly below. The wire is supported at the mid point by a fibreglass pole, and a spring counter-weight ( see inset ) running through a pulley tied at the highest point I could reach to a tree at the far end.
The (in)famous loading coil, ( posts dated Feb 19th & Sept 13th 2010 ), will still have to be pressed into service; but fortunately it will be installed inside my radio room. What a huge relief that I will no longer have to use the coil outdoors or carry out frequent maintenance on it inspite of the snow and ice, as with the previous antenna !
My last attempt to put up a different antenna for long wave was in 2009. It was a much more complex design, both electrically and mechanically, requiring 'miles' of wire. It would have been an excellent performer. Sadly it never came to fruition, being blown down / away four times during summer thunder storms before I had even finished building it. There was an important lesson to be learnt from that ! It's better to have a simple antenna than no antenna.
While the performance of the new antenna will be inferior to the one I didn't complete, it should out-perform the last operational one.

More "firsts" on longwave

Yesterday evening, Szigy, callsign YO2IS, in Timisoara, Romania, 710 kms away, and I had a contact on the 2190m longwave band, which we will claim as the first ever Romania - Poland contact on that band, thereby adding Romania to my two prior "firsts" with the Czech Republic and Belarus.
I copy part of Szigy's email which he sent to me soon after our meeting 'on the air', particularly because it emphasises how challenging amateur radio communication is on longwave; as I know only too well myself, even over distances of just a few hundred kilometres. Szigy wrote:

"Dear Steve pleased to run a fine QSO with you, the very first SP-YO on 2.2Km. Signal was nice but with a deep QSB on the midle of the QSO. At the beginning had some problem with a flashover in the teflon feedtrough my window, it take one hour to change the isolator.Will send you a direct QSL in the next days. Once more thanks for the new one ! Have fun on VLF it's always a big chalenge, gl."

One of the challenges is typically the use of short inefficient antennas, ( because of the nearly 2.2km wavelength ), causing high voltages of several KV to appear at various places in the antenna system. Unluckily for Szigy during our contact, he had to take time out to tackle a problem of insulator flashover !
Earlier this week, I cleared ice and snow from my antenna in order to make it useable once more; but even then I had a flashover problem which I was able to prevent happening again, and fortunately nothing went wrong at my end during the contact with Szigy.

Stop press: In the last few minutes I have achieved another "first", Estonia. Incredible conditions on longwave this weekend, and some stations active making the most of them. What a start to 2011 on 2190 !

Four on longwave

Most weekends, except in summer, I am transmitting my radio signal on longwave, ( 2190m / 137.7KHz ), and hoping someone will reply. Usually my signal goes unanswered as no one else is about; but last night Marek, a Polish radio amateur, callsign SP2OVY, from near Gdansk, called me. I had never received his signal before. So I assume that he has only recently begun to transmit on longwave. To my knowledge there are now 4 Polish stations, including myself, who have transmitters for the 2190m band; though I am aware of a few others who monitor on receive only. Two years ago I was the only one active on longwave in Poland. So the numbers are gradually increasing.
The distance between Marek and me is only 277kms; but I was happy my signal made it that far as snow on my antenna had significantly detuned it. We had a successful 2-way contact, ( report "O" bothways ), ending in the early hours of this morning.
The screen capture shows his slow morse ( QRSS ) signal to which I have added the letters; of course 'E' and 'N' were the following two letters on the next screen capture, ( not shown ).
I am still using the same home-made transmitter and antenna which I featured on the blog on 25th January and 19th February.

Loopy thoughts

I've been sorting through my stock of coax cables. If I join together several lengths of the same thickness of 6mm, I could make one length of 70 metres. Perhaps it will be enough to construct a reasonably effective rectangular loop antenna for transmission on the longwave 2190m band.
So let's see.
I could support it vertically from two trees in the garden 20 metres apart, with the vertical plane running N-S. The area enclosed by the loop would be 300 square metres.
After doing some quick calculations, I predict Rrad = 121 micro Ohms, and efficiency = 0.0076%, assuming rf losses = 1.6 Ohms.
In terms of efficiency it will be nearly 4dB worse than my existing longwave Marconi antenna. Another limitation is the loop's bi-directionality, ( Marconi omni-directional ); so radiation broadside ( E-W ) could be 30dB down on end-fire direction ( N-S ).
I wonder if making it will be worth the effort.
Has anyone made a longwave loop antenna of a similar size ?
If so I would be pleased to hear of your experiences with it.
I won't be buying a single 70m length of new coax just yet !

Weather bad, longwave good

Tonight it is snowing again. The large coil is outside and connected to my antenna, but has little protection from precipitation. Although the weather is poor, radio propagation conditions on longwave tonight have been good. I have just completed a contact with Gerhard in Austria. The screen shot shows him calling me at the start. The other horizontal lines are sidebands from the LORAN-C navigational system on 100KHz. There are LORAN-C sites in coastal regions of northern Europe. We have to put up with its interference until the system is supersceded by GPS. The sound it makes is like a steam locomotive travelling at 100mph. To our advantage, however, these 'lines' give a useful indication of propagation conditions on 136KHz, and were strong and clear tonight; hence the possibility for my contact with Gerhard.
My signal was also picked up 745 kms away in Nuernberg, Germany !

Friday night activity night

Yesterday evening the first activity period on longwave took place, to encourage Polish radio amateurs with longwave receiving and/or transmitting equipment to meet up "on the air". I think that in Poland only myself and one other guy can transmit on 2190m wavelength. Amateurs' antennas for this wavelength are relatively short and inefficient. So we have to transmit information slowly in a very narrow bandwidth to have any chance of being picked up. As an example, the screen capture shows how my slow morse signal, ( 4 sec dot , 12 sec dash ), was received by another Polish receiving station during this activity period.

Extreme loading coil appears in ham press

A description and picture featuring the massive loading coil I use with my Marconi antenna for 136KHz, have recently appeared in RadCom, the monthly magazine of the Radio Society of Great Britain, RSGB, December 2009, page 29. ( click on the post title to visit the RSGB web site ).
The main winding consists of about 400 turns on a 15cm diameter, 108cm long, sewer pipe and has multiple tapping points. The rotatable variometer winding inside is made from 37 turns on a 11cm diameter plastic water-pipe. The upturned plastic food container on top keeps water out.
The impedance matching network to the 50 Ohm coaxial cable feeder from the transmitter uses an ETD44 transformer core with a 9 turn primary winding and a 20 turn secondary winding. I can obtain a perfect match with this method, though occasionally there is slight detuning of the antenna system owing to environmental effects, requiring readjustment of the variometer.

Award arrives

The award that I mentioned in my last posting has just arrived by post; very colourful it is too. It will look even more impressive when framed and hanging on the wall in my radio room.

136KHz Award

PZK, the Polish national amateur radio society, has awarded me with a certificate in recognition of my achievements in longwave radio communication. And I even get a mention on the PZK web site http://www.awards.pzk.org.pl
( click on post title )