Military Reliance on HF on the Rise?

I am sharing an email I received from Jeorg at regarding increased solar propagation and the threat to satellite and wired communications in times of war. For those who may not know, Klingenfuss aggregates utility, shortwave, military and other HF frequency lists in book and CD form. I received this email as a customer having purchased their latest “Super CD” earlier this year. I am not affiliated with them other than as a customer, and this email did not come to me as a sales pitch. I do however think their software is a good value for the money. for what that may be worth! – Robert, K4PKM

Dear friends,
solar activity is increasing rapidly and provides excellent HF
propagation conditions on frequencies above 20 MHz as well. Sunspot
numbers have ramped up pretty fast: in February 2023, the NOAA number
already reached more than 200 – while the maximum of the current
solar cycle 25 is expected not before mid-2025! See our screenshot of
2 April 2023 at
In these times of war, remember the key fact: shortwave = HF is the
only medium for inter-national and inter-continental communication
that, unlike e.g. SATCOM, landline connections, and submarine cables,
cannot be blocked, censored, or cut off. What’s more, there are no
call costs or monthly fees.
Increased vulnerabilities to cyber and SATCOM – coupled with state-of-
the-art HF communications capability and capacity – is making
military services worldwide rethink their communications planning.
Says DA Reporter at
“In a modern threat environment, access to local communication
infrastructure or satellite communication cannot be assured. Having a
communications capability that can work seamlessly with the
Australian Defence Force and its allies is essential. Starting in
October 2023 under the JP9101 – Enhanced Defence High Frequency
Communications System program, the new system will provide Australian
and allied armed forces with the ability to securely communicate
using voice and other data from almost any location across the
Robert Gulley, K4PKM, is the author of this post and a regular contributor to the SWLing Post.
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8 thoughts on “Military Reliance on HF on the Rise?

  1. Jens Jensen

    Well said. Much new technology on the HF MIL Radio arena including Wide- Band HF, more secure waveforms, better interoperability among vendors and more efficient use of radio spectrum. It’s going to be a dynamic decade for HF Plans & Operations.
    Cheers/ Jens

  2. mangosman

    SDR technology in transmitters
    The reverse of the SDR technology is used in transmitters where the information is filtered and modulated in a computer chip which uses the appropriate firmware. The carrier frequency is around 12 kHz which is easy for the computer to handle. This includes AM, SSB, CW, FM, and digital modes which may or maybe not encrypted. The resulting signal is converted from digital to analog. The modulated 12 kHz signal is then fed into an up converter with digital signal from a programmable oscillator to convert the output to the transmission frequency. Then that signal is amplified, output filtered to prevent out of band signals an fed into an antenna.

  3. Waldo

    Hi there.
    Solar Cycle is with us and that is a fact. Radio propagation is improving and I expect we´ll have a few years of listening pleasure ahead.
    Long gone are the golden days of HF. Marine, Point to Point Radio-telephone, most of Aviation, and of course Broadcasting and all the services that relied on radio for day to day operations.
    More and more digital communications and the majority encrypted, are “on the air”, that makes SWL challenging but somehow difficult to keep abreast with. In reality such data decoder systems as go2MONITOR, W-CODE and the like are way way off the pecuniary possibility of us mortals.
    On the side for city dwellers the noise has increased to such a high levels that except if living in the countryside renders listening quite difficult.
    As an aid there are an ever increasing constellation of SDR receivers online (that I myself think of as cheat – no pun intended).
    The net has become an indispensable tool for everyday use, namely work or entertainment but alas, also something to be taken with care, deceit and falsehoods are among other risks and the utmost caution ought to be exercised to fish the right information. Any single search might give us hundreds if not thousand of results.
    Today we have web pages, blogs, forums, groups and the like where to find information.
    Preppers and off-the-grid promoters, books and movies among others are giving warnings of the possibility of a natural cause or man made crisis leaving us without all means of communications that we have for granted.
    I guess a bit appalling and remote but a possibility anyhow.
    OK, tube radios… And the power to crank it???
    Sorry for this lengthy and perhaps off-topic intro.
    I myself bought the Guide to Utility Stations from Klingenfuss a few years ago though in book format. Treasured it for many years and used almost every day until it become obsolete and by that time Internet was widely spread and my habits somehow changed. Now I rely on the Net to gather information. Not to diminish the wonderful work Klingenfuss is doing but I really think that the publications are somehow out of fashion. The mail appears to me a sales advertisement.
    But again as and old timer and former Merchant Marine radio operator I sorely miss the “set aside by technology” operation, the challenges of experimentation, the building of antennas to cope with the lean years of propagation, cross referencing and finding information in books and publications. Seldom I see a photo of a radio station or monitoring post without a computer. After many years I am thinking of buying the WRTH and perhaps the Guide to Utility Stations again.
    Going back to basics and enjoy the hobby. Not to run after the technology but going ahead of it as a human being controlling it and not the other way around.

    1. mangosman

      The Software Designed Receivers advantages
      They have the great characteristic of tuning almost between ‘DC and daylight’! Really around 100 kHz to over 2 GHz, giving more opportunity for a greater range of signals.
      A huge advantage is the ability to provide selectable variable width filtering with very steep sides, better than the inductance/ capacitance filter, mechanical and crystal filters. The decoding of signals is through algorithms for AM, SSB, CW, FM, and digital speech modes and digital broadcast modes. The digital modes are not present on all SDRs.
      They use PIN diode attenuators in the antenna input to reduce the signal strength of incoming signal depending on the detected signal level.
      There is a freedom from image frequency interference which occurs in superhetrodyne radios at double the intermediate frequency.
      They are also much cheaper to make.
      Very low power consumption which makes battery operation possible so you can go to an RF quiet area equipped with a portable antenna.

      What are the disadvantages?
      The input signal is converted from its original frequency to around 12 kHz rather than the superheterodyne’s intermediate frequencies which can be 10.7 MHz and 455/450 kHz.
      This requires a very linear downconverter and an oscillator free of harmonics, in addition the signal is then converted from analog to digital (the greater the number of bits per sample the more linear)
      To overcome the effect of strong signals including interference from arcing sources a tuned filter is needed at the antenna input. This costs money and is omitted in the cheaper and smaller receivers.
      SDR manufacturers, despite having a colour screen make no attempt to display analog slow and fast scan TV along with faxes typically of weather maps. It just requires the right firmware. Neither do they have the firmware to decode digital transmission modes for audio, pictures or text.
      It is a pity they don’t buy the licences for the digital reception algorithms, install the firmware and sell them as options.

      1. Waldo


        I agree with you with regard to SDR receivers, in fact I own an Airspy HF+ Discovery and RSPduo becoming my daily staple of monitoring equipment.
        My intention when stating that remote SDRs are a somehow a cheat was in regard to using the same to log stations as if were received in the home shack.
        Remotes are wonderful tools to check and cross reference, even to open new worlds but criterion is a must to be exercised when used to log and confirm reports.
        That said, I ought to apologize if any of my words offended. English is not my native language and very often I commit regrettable mistakes.

  4. mangosman

    There is also the use of HF for ‘Over the horizon radar’ which is used to detect boats the size of fishing trawlers from many thousands of km away.
    The use of digital transmission and its ability to be encrypted is not only used in mobile phones it is also available in the high frequency band and can transmit any type of data including text and images.

    Some military HF equipment manufacturers


    All very well but the advantages of HF are also its disagvantages too.

    I expect most military short range communication is now using encripted low VHF frequencies. As do the UK Police services.

    The western countries probably expect their communication infrastructure is very secure. But in the UK we still have the Post Office unable to send overseas parcels following a cyber attack weeks ago on their systems.

    The Russians seem to be using the Ukrainian cellular telephone systems a lot and the Ukrainians seem to be able to listen in to many of their converstaions to their advantage. There seems little information on the official Russian communications systems.


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