Shortwave 'bands' - why?

[stevehertz]

Why are shortwave stations grouped together in bands? eg 19m, 31m, 49m etc.

[G6Tanuki]

It helps listeners know where to look for broadcasts.

It keeps broadcast stations in manageable chunks of the spectrum and stops them spreading into areas of spectrum assigned to other services like aviation, military, shipping etc. (Though this was often not respected, in the Cold War era us Ham/SWL types had to put up with Communist intrusions into our 7.0-7.1MHz exclusive allocation from Radio Moscow , Tirana and Bulgaria).

It allows easy design of multi band bandspread SW radios with each band taking up the whole dial space so tuning SW broadcasts would be a lot easier than the usual nasty approach of covering 5.5 to 20-odd MHz in a single short wave band which with the usual 10 turns of the tuning knob to cover the entire swing of the tuning capacitor meant that you needed the skill of an experienced safecracker to tune a station.

[Radio Wrangler]

Frequency allocations are internationally coordinated below 30MHz. 30MHz was an arbitrarily chosen marker where Ionospheric propagation was considered likely below and unlikely above. National bodies got more freedom above 30MHz to go their own way a bit.

The MF-HF spectrum was carved up into broadcast bands, Maritime, Aeronautical, trunked comms, military, amateur bands etc etc. Modes were assigned and so on.

What we see today is what's left of all this planning as various services shift onto other methods.

Have a look at the ITU-R website for various bandplans.

David

[Ian - G4JQT]

Each band has different propagation characteristics too. The BBC might operate from the UK on 6 and 7 MHz for Europe, but 15 and 21 MHz for North America.

[Oldmadham]

Originally Posted by Ian - G4JQT

Each band has different propagation characteristics too. The BBC might operate from the UK on 6 and 7 MHz for Europe, but 15 and 21 MHz for North America.

Even within countries & States within those countries.

The now defunct VLW/VLX domestic shortwave outlets in Western Australia operated from Perth, transmitted on 6.14, 9.61, & 15.425 MHz depending upon target area in the Northern parts of the State & the time of day.

[Mark GØOIW]

Originally Posted by Oldmadham

The now defunct VLW/VLX domestic shortwave outlets in Western Australia operated from Perth, transmitted on 6.14, 9.61, & 15.425 MHz depending upon target area in the Northern parts of the State & the time of day.

Happy memories of listening to Radio Australia that used to put a huge signal into Britain at around Sunrise. Started with a kookaburra and Waltzing Matilda. Some of those Australian domestic stations on the lower SW frequencies also made it here when the conditions were right.

Then there were the broadcasts I couldn't understand. The announcer was obviously Australian, I could recognise a lot of the words, but it didn't make any sense. The language was Tok Pisin, of course.

[Mr 1936]

Hi

My interpretation is that as Shortwave services expanded, all the users (Amateur, Miitary, Commercial, Broadcasting etc) wanted a choice of frequencies to cater for different propagation conditions. The earliest reference I can find to any kind of "refereeing" of these competing claims on the HF spectrum seems to be the International Radiotelegraph Conference in Washington in 1927. Nearly 100 years ago !

I attach the allocations table which resulted from the conference, where everyone was given a number of "slices of the pie".

If you want to read the whole conference proceedings, see here: https://search.itu.int/history/Histo....43.en.100.pdf

I'd be interested if there was an earlier table than this.

[turretslug]

Originally Posted by Mark GØOIW

Happy memories of listening to Radio Australia that used to put a huge signal into Britain at around Sunrise. Started with a kookaburra and Waltzing Matilda. Some of those Australian domestic stations on the lower SW frequencies also made it here when the conditions were right.

Snap, 13m could come up with some good stuff at daybreak.

Interesting to note from that 1927 chart that the broadcasting allocations were quite narrow initially, maybe as it was realised just how effective the reach of HF broadcasting could be, so there was pressure for more generous span. Mind you, some broadcasters seemed to regard band edges as advisory anyway.... I wonder just how widely the higher frequency bands were used then, 49m probably wouldn't have been too much of a stretch but 13m would have been a bit of a challenge. I'm thinking of the interested but not necessarily technically proficient SWL here, rather than radio amateurs who would have seen higher and higher frequencies as an entertaining goal even if much tweakery was involved.

[Graham G3ZVT]

Originally Posted by Mark GØOIW

Then there were the broadcasts I couldn't understand. The announcer was obviously Australian, I could recognise a lot of the words, but it didn't make any sense. The language was Tok Pisin, of course.

What struck me when I used to listen in the 60s 70s, was that the English language announcers didn't sound particularly Australian, as if there was a bias towards RP voices.

[Pfraser]

Originally Posted by turretslug

Snap, 13m could come up with some good stuff at daybreak.

Interesting to note from that 1927 chart that the broadcasting allocations were quite narrow initially, maybe as it was realised just how effective the reach of HF broadcasting could be, so there was pressure for more generous span. Mind you, some broadcasters seemed to regard band edges as advisory anyway.... I wonder just how widely the higher frequency bands were used then, 49m probably wouldn't have been too much of a stretch but 13m would have been a bit of a challenge. I'm thinking of the interested but not necessarily technically proficient SWL here, rather than radio amateurs who would have seen higher and higher frequencies as an entertaining goal even if much tweakery was involved.

The FCC authorised a tempting technical challenge for the SWL in the 1930s. This was the brief era of the apex stations, operating between 25-27Mc and 31-44Mc, plus some channels higher up.

Given the relative crudity of short wave transmitters in those days, I would expect there would have been many harmonic radiations about. 'Accidental' higher frequency DX for the adventurous SWL!

[emeritus]

"Wireless World" used to periodically publish a large wall chart covering the entire radio spectrum showing which services were occupying each part of the spectrum. Somewhere in the shed I still have one that was included in a mid-1980's issue.

[Oldmadham]

Originally Posted by Mark GØOIW

Happy memories of listening to Radio Australia that used to put a huge signal into Britain at around Sunrise. Started with a kookaburra and Waltzing Matilda. Some of those Australian domestic stations on the lower SW frequencies also made it here when the conditions were right.

Then there were the broadcasts I couldn't understand. The announcer was obviously Australian, I could recognise a lot of the words, but it didn't make any sense. The language was Tok Pisin, of course.

Although VLX/VLW were intended for domestic audiences within WA, the ABC received plenty of notifications of Dx reception far afield.

At this point, I'd like to mention a strange one--VOA on around 1400kHz in the AM BC band.
In the 1970s, driving home after midnight from "afternoon shift" at the ABW2 transmitter in Perth, I could consistently receive this outlet on my car radio, first in English then in another language (can't remember which).

All the info I can find on old VOA outlets seems to deny the existence of one on MF, although one ham in the USA suggested that it might have been retransmitted on the US Armed Forces Radio Network.

[Richard_FM]

Originally Posted by Graham G3ZVT

What struck me when I used to listen in the 60s 70s, was that the English language announcers didn't sound particularly Australian, as if there was a bias towards RP voices.

It seemed more common for educated Australians to soften their accents back then.

[dave walsh]

I bought a GEC Export "woodie" [5542] at Punnets Town recently. No LW of course but the SW band has 6 tracks with designated frequencies leading to 6 Bandspread Dials 6" long ie 31m 25 19 16 13 and 11m! That's putting stations in an identifiable place but with a great ease of access I suspect.

Dave W

[russell_w_b]

Originally Posted by Graham G3ZVT

What struck me when I used to listen in the 60s 70s, was that the English language announcers didn't sound particularly Australian, as if there was a bias towards RP voices.

You should've heard Steve Wright when he used to broadcast on the BBC WS. He was the self-same Steve Wright who broadcast on BBC R2 'in the afternoon' but they could've been two different blokes.

[Hybrid tellies]

When I first started listening to broadcasts on my first short wave radio back in the early 1970's I was advised that as a general rule of thumb use the higher frequencies during the day and the lower frequencies at night, then for a few gours either side od sunset and sunrise use the middle frequencies.

So during the day, 19m, 16m, 13m, and sometimes 11m are best.
At night 75m, 49m and 41m are best.
For a few hours either side of sunset and sunrise 31m and 25m are best. This does work well and if you study the frequency schedules of most broadcasters its a rule that many them go by.

Of course there are some variables due to seasons and the where you are in the sunspot cycle

[russell_w_b]

Originally Posted by Hybrid tellies

When I first started listening to broadcasts on my first short wave radio back in the early 1970's I was advised that as a general rule of thumb use the higher frequencies during the day and the lower frequencies at night, then for a few gours either side od sunset and sunrise use the middle frequencies.

Very true: plus lower freqs in winter and higher in summer; higher at peak of sunspot cycle (the 21MHz and 17MHz transmitter final anode coils get very hot and those leather gauntlets to band-change were most definitely needed!)

Evening shift was always busiest at Skelton with perhaps thirteen band-changes over six hours. Day turned to night and the frequencies and bands changed to reflect ( ) ionospheric conditions.

[Synchrodyne]

Pretty much all HF users had/have the same requirement for frequency agility according to sending and receiving locations and time of day. Thus all needed several-to-many allocations throughout the 1.6 to 30 MHz range, or in some cases, such as tropical broadcasting, over part of it. Hence the “slicing and dicing” of that range into a large number of relatively narrow bands. Some, such as maritime mobile, had a preference for harmonic relationships amongst at least some of their allocated bands, which probably complicated assignments, and might have resulted in apparently odd positioning for services, such as shortwave broadcasting, that did not have this requirement.

Originally Posted by dave walsh

I bought a GEC Export "woodie" [5542] at Punnets Town recently. No LW of course but the SW band has 6 tracks with designated frequencies leading to 6 Bandspread Dials 6" long ie 31m 25 19 16 13 and 11m! That's putting stations in an identifiable place but with a great ease of access I suspect.

Many of the UK setmakers offered export receivers with electrical bandspread tuning through to around the mid/late 1950s. Which bands they chose to bandspread and how they did it varied. The larger organizations generally developed their own approaches, but those at the smaller end used bought in units, such as the Weyrad bandspread front end assembly. Amongst those with interesting circuit aspects were Elco (A182) and Murphy (TA160). Radiogram chassis makers Armstrong and Dynatron also had bandspread models, as did tuner specialist Chapman. Pye authored an IEE paper on the subject. (D.H. Hughes; ,”The Design of Band-Spread Tuned Circuits for Broadcast Receivers”, 1945 October. L.A. Moxon of Murphy devoted some space to SW BC reception and bandspreading in his book “Recent Advances in Radio Receivers” (Cambridge University Press, 1949). Some of the approaches delineated therein were found in the Murphy TA160 receiver.


Cheers,

[Mr 1936]

Hi

Mention of L.A. Moxon (Leslie Moxon G6XN) reminds me of his excellent book "HF Antennas for all Locations". This covers both transmitting and receiving shortwave antennas and is very readable. Published in the 1980's but readily available.

[turretslug]

Originally Posted by Hybrid tellies

When I first started listening to broadcasts on my first short wave radio back in the early 1970's I was advised that as a general rule of thumb use the higher frequencies during the day and the lower frequencies at night, then for a few gours either side od sunset and sunrise use the middle frequencies.

So during the day, 19m, 16m, 13m, and sometimes 11m are best.
At night 75m, 49m and 41m are best.
For a few hours either side of sunset and sunrise 31m and 25m are best. This does work well and if you study the frequency schedules of most broadcasters its a rule that many them go by.

Of course there are some variables due to seasons and the where you are in the sunspot cycle

The "terminator" was a useful aid and guide for SWL long before Mr. Schwarzenegger popularised it!