# Mimco Crusader Transmitter



## R651400 (Jun 18, 2005)

Follow-up from the Globespan *here*


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## sparks69 (Dec 18, 2005)

Every time I turned that big knob in the middle I held my breath !


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## Varley (Oct 1, 2006)

Why on earth the 'big knob' was not interlocked with the HT switch will remain a carbonised mystery.


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## DickGraham (Oct 2, 2017)

Sailed with one on the Fleetbank which was a bit of an upgrade from the 'Span VI I'd sailed with on the previous trip on Weybank (LOL)


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## sparks69 (Dec 18, 2005)

I did like the power though. The fluorescent tubes in the radio room would flash when keying on 4 & 6 MHz.


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## Paul Braxton (Jul 21, 2005)

... and the metal parts of the earphones would often burn your ears a bit on the old 'Serenia'...


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## Ron Stringer (Mar 15, 2005)

Paul Braxton said:


> ... and the metal parts of the earphones would often burn your ears a bit on the old 'Serenia'...


It wasn't just the use of 'open' antenna feeders (copper tubing) between the transmitter and the external antenna that caused such phenomena. Satisfactory grounding (earthing) of the transmitter was a cause of many problems that technicians, including those working in the installation planning department of MIMCo, didn't fully appreciate. For the _Oceanspan _range, tinned copper wire 7/.029" connecting the transmitter cabinet to a brass bolt screwed into the metal deck of the radio room was deemed adequate and, with the low powered _Oceanspan _range, did not exhibit any problems. This continued with _Worldspan _and _Globespan _and I can confirm that in hot weather, sitting at the key wearing only a towel around the waist, you had to be damned careful to keep the headphone cord away from your sweaty body if you wanted to avoid a painful reminder that RF does burn skin.

For the _Crusader_, after many initial problems, the earthing arrangements were improved somewhat to 6-inch wide, 0.4mm thick copper strip replacing the wire. With the higher power of that transmitter however, problems persisted, made worse by the changes in ship design that enforced the use of short, inefficient antenna arrangements. On some ships the length of copper tubing within the radio room was a significant portion of the overall antenna length. 

To try to improve matters when _Conqueror _came along, I won a long struggle to convince the installation planning department, and others, that a minimum 12-inch strip must be used for the grounding. The transmitter cabinet was provided with appropriate connection arrangements for the wider strip and a specific grounding diagram was produced and included in the installation manual. Despite the power increase of _Conqueror _over _Crusader_, we had very few reports of operational problems with unwanted effects. A couple of years after the _Conqueror _entered service, I received a grudging acknowledgement from the head of the department that the transmitter had given them fewer problems than its predecessor. 

Of course the real solution was to re-locate the transmitter's antenna tuning/matching arrangements out of the radio room, to the base of the antenna, being connected to the transmitter's 50-ohm output using co-axial feeder. Then all was calm within, as the transmitter's RF output was conducted into the antenna instead of bouncing around the radio room. This had become the standard for most manufacturers by the time that the radio room disappeared from ships and communication was transferred to the Bridge and the cabin.


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## J. Davies (Dec 29, 2010)

Slightly off topic, a party trick which one captain particularly enjoyed was tuning up on 512 KHz or so with knee down on key, holding a lead pencil with the thumb on the blunt end towards the copper tube antenna feeder. A gap of a few inches would produce a long hissing orange RF arc in which with the other hand you could introduce a slip of newspaper. This would burst into flames and made a good captain's *** lighter when he lost his matches.
The only downside was a small but painless RF burn the size of a pin***** on the thumb.
It is interesting to note that at higher frequencies up to HF the colour of the RF arc turned progressively purple and the audio hissing tone increased. Someone should make a study of this phenomenon .


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## Varley (Oct 1, 2006)

Send me at once a Crusader, an appropriate gap and a good Captain. I will start the research upon receipt (might we also need a planck?).


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## R651400 (Jun 18, 2005)

Where's our Troppo to enquire if this corona discharge was actually radiating and causing Class B QRM on the international distress frequency of 500 kc/s?


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## CrazySparks (Apr 21, 2008)

I think it was on the Riverbank in around 77 that keying the main Tx (Conqueror or Crusader - I don't recall which) that keying on 22MHz literally stopped the ship - interfered with engine room electronics somehow. Good thing it wasn't any other band! My first trip as solo R/O!


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## Devans47 (Apr 24, 2013)

*Crusader transmitter.*

Found this MIMCO Crusader in the back room of a maritime museum in Port Chalmers NZ last, while on a Holland America cruise.


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## Varley (Oct 1, 2006)

That looks in cracking condition.


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## IvortheEngine (Sep 2, 2016)

Cracking or crackling?


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## aussiesparks (Nov 11, 2009)

J. Davies said:


> Slightly off topic, a party trick which one captain particularly enjoyed was tuning up on 512 KHz or so with knee down on key, holding a lead pencil with the thumb on the blunt end towards the copper tube antenna feeder. A gap of a few inches would produce a long hissing orange RF arc in which with the other hand you could introduce a slip of newspaper. This would burst into flames and made a good captain's *** lighter when he lost his matches.
> The only downside was a small but painless RF burn the size of a pin***** on the thumb.
> It is interesting to note that at higher frequencies up to HF the colour of the RF arc turned progressively purple and the audio hissing tone increased. Someone should make a study of this phenomenon .


Same trick was used at the Northern Counties Radio with an Ocean Span, however most pencils have paint etc over the end of them and this stopped problems however one day a student tried it with a pencil with a bare end , this was the same as touching a bare antenna and he was thrown across the radio room, luckily unhurt


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## J. Davies (Dec 29, 2010)

Devans47 said:


> Found this MIMCO Crusader in the back room of a maritime museum in Port Chalmers NZ last, while on a Holland America cruise.
> View attachment 191157
> 
> 
> View attachment 191159


I never thought I could get all bleary-eyed and nostalgic over an old but rather magical lump of British technology.


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