Why 87Hz for mole/heyphone and nicolas?

Antwan

Antwan

Member
Just a curious thought occurred today, why was 87Hz chosen as the frequency for these devices?

I'm wondering if a lot of the 'beating' interference encountered around populated areas could be attributed to the alignment with three phase equipment running at the same frequency and stepping down by 10hz (allowing for bandwidth) or up by 20hz (allowing for the harmonics of the 50hz single phase) would help? or am I thinking too simplistic as per usual  :-\

 
shotlighter

shotlighter

Active member
Antwan said:
Just a curious thought occurred today, why was 87Hz chosen as the frequency for these devices?

I'm wondering if a lot of the 'beating' interference encountered around populated areas could be attributed to the alignment with three phase equipment running at the same frequency and stepping down by 10hz (allowing for bandwidth) or up by 20hz (allowing for the harmonics of the 50hz single phase) would help? or am I thinking too simplistic as per usual  :-\
Click to expand...
It's 87kHz not Hz.
It's a long time ago but I think I've a copy of some of the original paperwork somewhere.
edit, Ive found it & the name of a certain Stuart France looms ever present.
I thing if anyone knows, he should!
 
wellyjen

wellyjen

Well-known member
Once 87kHz was chosen it stuck. Heyphones and Nicola radios can talk to each other, which wouldn't have been possible with a different frequency. No idea if Molephones were interoperable as they were before my time, but possible. Why 87kHz specifically? No idea.
 
paul

paul

Moderator
From https://pe2bz.philpem.me.uk/Comm/-%20ELF-VLF/-%20ELF-Theory/-%20CaveTheory/CaveRadio1/System-Nicola-Mk2/SYTEME_NICOLA_Mk2.html

The reception underground is often much better underground than on the surface. This is due to the high level of atmospheric disturbance in the LF band. Lightning strikes produce strong signals in the LF band which will propogate up to a 1000km due to the ground effect. Undergound these parasitic disturbances may be significantly attenuated (unless the cave is quite shallow). These noise sources will vary enormously from one day to the next and form day to night, due to the drastic changes in propogation conditions for these perturbing sources.

The Loran C transmitter also causes considerable disturbance in the region 80-130kHz. At the 87kHz frequency currently used in the system Nicola, this means that although over 1km is sometimes possible, in practice it is best to limit the distance to 500m to ensure reasonable reception is achieved on the surface. This distance is normally sufficent for even the deepest caves in France due to the fact the often the surface above the deepest part of the cave is often well below the level of the entrance. In the case where large distances are to be attempted then it is often useful to consider the geology so as to avoid passing through more comnductive strata. Sometimes finding the outcrop on the surface in shich the underground party is situated is sometimes beneficial. Once a contact is made, if the signal is weak it is often worth moving to improve the signal strength (as indicated above by maximising the received signal strength with a loop on the surface while the underground team connect their radio to an automatic beacon).
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and from https://klubnl.pl/wpr/en/index.php/2019/08/21/how-cave-communications-works/

The Molephone designed by Bob Mackin in the ?70s was one of the first devices that enabled voice communications through rock. Unfortunately the schematics are not avaliable. This device used SSB on 87kHz. The antenna was a multiturn loop with about 1m diameter.

Since that time most devices use  87kHz USB (or DSB) to be compatible. The most popular are Heyphone and Systeme Nikola. Usually the power is in the order of 10W to keep the weight of the equipment and power sources low.
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P

PeteA

New member
it is possible to change frequency on the Nicola 3 radios. This was added so that the Loran signal could be avoided if proving a problem.

A futher consideration is location finding, where lower frequencies provide better results.
 
shotlighter

shotlighter

Active member
PeteA said:
it is possible to change frequency on the Nicola 3 radios. This was added so that the Loran signal could be avoided if proving a problem.

A futher consideration is location finding, where lower frequencies provide better results.
Click to expand...
Most (all?) Loran transmitters have been shut down now, so should no longer be a problem.
I was reading through some of the old notes that I have on cave radio development & was fascinated to see that the French had experimented with 160M C.W.
Seems it worked quite well, from what I can tell with my limited French.
 
Antwan

Antwan

Member
shotlighter said:
Antwan said:
Just a curious thought occurred today, why was 87Hz chosen as the frequency for these devices?

I'm wondering if a lot of the 'beating' interference encountered around populated areas could be attributed to the alignment with three phase equipment running at the same frequency and stepping down by 10hz (allowing for bandwidth) or up by 20hz (allowing for the harmonics of the 50hz single phase) would help? or am I thinking too simplistic as per usual  :-\
Click to expand...
It's 87kHz not Hz.
Click to expand...

Of course it is! Makes the second half of my post slightly mute, I should sleep on any theories that arise after 8bhours graft and 5 hours of university study in the same day  :-[
 
F

Fjell

Well-known member
shotlighter said:
PeteA said:
it is possible to change frequency on the Nicola 3 radios. This was added so that the Loran signal could be avoided if proving a problem.

A futher consideration is location finding, where lower frequencies provide better results.
Click to expand...
Most (all?) Loran transmitters have been shut down now, so should no longer be a problem.
I was reading through some of the old notes that I have on cave radio development & was fascinated to see that the French had experimented with 160M C.W.
Seems it worked quite well, from what I can tell with my limited French.
Click to expand...

Loran is very far from dead. It is now the living dead as it is proposed to build a new system in Europe and the US to cope with spoofing of satellites for position and timing. And you will be glad to know it seems to be proposed to use 90-110 kHz.

As the EU threw the UK out of Gallileo and EGNOS, the UK is testing via Inmarsat for GPS error (and timing?) and who knows if the UK will also resurrect Loran, possibly with the Americans to replace the EU system for when we need to bomb them.

If the above isn't completely clear, the UK intends to a) irretrievably get into bed with the US b) Duplicate the EU system over Europe. I think the EU doing what they did in 2017 is going to be the really quite atrocious error everyone thought it was at the time. It has poisoned the well ever since at the strategic level, forget fishing boats.

What larx.
 
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