R1155 question

[Radio_Dave]

I just got another R1155.B but it has no HF chokes. The label on the front shows it has had two RAF modifications. Could one of those mods removed the HF chokes or did this variant not always have them?

Thanks
David

[Keith]

The chokes shown in your picture are L24 used in the RF switching circuitry for direction finding (looks like one of them has come adrift from its mounting). I would have thought they would be fitted to all variants but may have been removed in a subsequent hamification.

[Radio_Dave]

Thanks for the reply Keith, but I'm asking about the missing HF chokes which I thought were fitted to all R1155B's?

Here's a photo showing them on my other R1155B

Thanks
David

[Keith]

Hmm - interesting. Neither of my 1155's (L and M?) have those fitted. I wonder where they are electrically.

[Radio_Dave]

From what I've found on the internet the "B" is an "A" model with these HF chokes fitted. Their purpose was to stop radar interference, which is why the "B" was used in aircraft.

David

[John H.]

Hi Dave,
You are right, HF chokes 1 to 6 were fitted to the B and F versions for radar interference supression. A.P 2548A Vol 1 Fig 3A refers.

Circuit wise,
HFC`s 1 & 2 are in the loop aerial input (P3). HFC 3 is on HF aerial input (P1). HFC 4 is on MF trailing aerial input (P1). HFC 5 goes to the top caps of V1&V2 (D/F switch speed) and RFC 6 to the top cap of V3 in series with L33.
Hope this helps, John.

[Radio_Dave]

I can't see any benefit in removing them, so I guess my "B" never had them fitted, which therefore means it isn't a "B"

Thanks
David

[AC/HL]

You'll have to keep it away from the Radar, then!
I'd guess most interested people have seen this site:http://www.vk2bv.org/radio/r1155.htm, giving information on the mods