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Active Antenna Outfit AVK


Michael O'Beirne
 

Good morning team

 

I have an interest in Marconi’s Active Antenna Outfit AVK, developed as the prime warship’s VLF-HF receiving aerial for the Navy’s ICS3 radio system in the mid-1970s. 

 

It’s basically a strong cabinet 19in h x 15in w x 11.75in d.  On top is a big ceramic feed through insulator supporting a robust whip about 5ft long.  Two are usually fitted, one on each side of the roof of the ship’s bridge.

 

It covers 10kHz to 30MHz.

 

In order to cope with a 1kW transmission from the TX whips about 50 metres aft (or less), the input amp is valved.  The PSU is built in as a separate module and is fed from 115V AC.  This is odd cos naval vessels are all 240V or three phase, and I assume it’s a safety measure in the same way as 115V is used on building sites via the ubiquitous yellow transformer boxes.

 

In order to cover this wide frequency range I suspect it’s a cathode follower using something like a 5B254.  All the transistorised designs I have seen so far employ various ferrite cores for balance, matching and feedback, and most tail off below 100kHz.

 

The only info I can find on-line is the usual Navy’s one page Data Summary and an article in a Marconi in-house mag.

 

Does anyone have a circuit or a full handbook?  The reference is BR 800.  One or two scrapped from ships appear to have been on eBay so there can’t be a security issue after all these years.

 

Thanks

 

73s

Michael

G8MOB

 

 


BillAtkins
 

Michael,

I served in HMS Glamorgan 1979-81 and as far as I can remember we only had one AVK and it was fitted port side, near the hangar.  My understanding at the time was that the aerial was EMP-proof (hence the valve). 

The ship's generators on H.M. Ships of the day produced three-phase 440V AC 60 Hz which powered larger systems and machinery directly, and was reduced by transformers and motor-generators to the voltages (and frequencies - e.g. 400 Hz for synchros) required by the other systems on board.  There was only a small requirement for 230V, as most electronic equipment, lighting and domestic appliances (such as flat-irons) ran on 115V.  Small transformers were provided on messdecks for shavers.

Best regards  ..................  Bill Atkins


Michael O'Beirne
 

Bill

 

Thank you for your advice. 

 

I’d be very surprised if the AVK was mounted anywhere aft, near the helicopter hanger, because the aim was to get it as far as possible away from the transmit whips which, I suspect, were mounted on the roof of the hanger or close by.  Hence all the photos I have seen and in the Marconi literature, the AVKs are shown mounted on the roof of the bridge, usually two, because they were the prime rx aerial and you’d need redundancy if one failed or perhaps was damaged in a fire fight. A single 40mm shell hitting square on would probably be enough to knock one out despite the robustness of the cabinet.

 

BTW there is an interesting conference report in the IEE archives dated 1946 about WW2 comms.  One continuing problem for the Navy was their wire aerials being shot down by their own high-angle AA guns – eg the Vickers pompoms.

 

All noted about electric distribution.  I was told 40 years ago by an RV engineering officer (now sadly long departed) that it was mainly 240V AC, whereas a lot of merchant ships were still 110V DC, but that may have applied to older RN ships.

 

73s

Michael

G8MOB

 

 

From: wireless-set-no19@groups.io <wireless-set-no19@groups.io> On Behalf Of BillAtkins via groups.io
Sent: 27 November 2020 17:08
To: wireless-set-no19@groups.io
Subject: Re: [wireless-set-no19] Active Antenna Outfit AVK

 

Michael,

I served in HMS Glamorgan 1979-81 and as far as I can remember we only had one AVK and it was fitted port side, near the hangar.  My understanding at the time was that the aerial was EMP-proof (hence the valve). 

The ship's generators on H.M. Ships of the day produced three-phase 440V AC 60 Hz which powered larger systems and machinery directly, and was reduced by transformers and motor-generators to the voltages (and frequencies - e.g. 400 Hz for synchros) required by the other systems on board.  There was only a small requirement for 230V, as most electronic equipment, lighting and domestic appliances (such as flat-irons) ran on 115V.  Small transformers were provided on messdecks for shavers.

Best regards  ..................  Bill Atkins

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