Roman digits and radar types

[CJE]

Hello,

I know that the roman digits painted on the nose or fin of the German night-fighters refered to the type of radar they were equiped with.
But what were the equivalences?

Thanks.

Chris

[David E. Brown]

Hi Chris,

The Roman numerals referred not to the radar type per se, but the respective device's frequency and/or frequency range.

These letters were painted on the nose or tail and later in the war combined with Arabic letters designating the version of the radar (e.g. FuG 220), and additional equipment, e.g. "R" for “Rückwärts-Warngerät” (tail-warning device). These latter combinations were painted in various positions on the tailfins of the Ju88G, He219A and Bf110G sometimes in black but more often in white.

I don't have access to my files at the moment, so hopefully someone can post more complete and related information here for everyone's benefit.

Cheers,

David

[RodM]

Hi Chris,

on late-war types at least, the Roman digits were related to the range of Streuwellen (spot frequencies) that the installed radar could be tuned into.

For example, FuG.220 had provision for seven spot frequencies (I through to VII, wave lengths 2.37 to 4.70 metres), and FuG.218 had provision for six spot frequencies (wave lengths 1.60 to 1.80 metres). Individual radars were not neccessarily equipped with the entire range of available Streuwellen, and the Luftwaffe placed restrictions on the operational employment and general handling of aircraft equipped with radars utilising spot frequencies that appeared to be undiscovered by the Allies and hence less susceptable to jamming.

As a case in point, in October 1944, the Luftwaffe's position was that only aircraft installed with SN-2 radars equipped with spot frequencies IV (wave length 3.3 m.) and V (wave length 3.7 m.) could be used over Allied-controlled or neutral territory, while those equipped with SN-2 spot frequency VI (wave length 4.1 m.) could not. This was to ensure that the radars equipped with Streuwelle VI did not fall into Allied hands. In late January 1945, this restriction was completely lifted.

Cheers

Rod

[CJE]

Most interesting.
Thanks.

Chris

[CJE]

Sorry to come back on this issue, but the picture is not clear.

@RodM:

You talk about Streuwelle (frequency) and give examples in meters : IV = 3.3 m. I thought the SN-2 was... centrimetric.

Moreover, meters are used for wave length, while frequency is measured in MHz (from 37,5 to 118 MHz as far the SN-2 is concerned).

Can you be more specific?

Thank you.

Chris

[Snautzer]

see here: https://aobauer.home.xs4all.nl/handbooks.htm

[CJE]

Thanks.
However, I hate treasure hunt and I would appreciate a more direct answer.

Chris

[RodM]

Originally Posted by CJE

You talk about Streuwelle (frequency) and give examples in meters : IV = 3.3 m. I thought the SN-2 was... centrimetric.

Moreover, meters are used for wave length, while frequency is measured in MHz (from 37,5 to 118 MHz as far the SN-2 is concerned).

Hi Chris,

firstly, SN-2 operated in the metric band (German: Ultrakurzwellen, Ultra Short Wave), which is one of the reasons why it was so easily jammed from August 1944 onwards. The only German centimetric AI radar to see a modicum of operational service was FuG.240 Berlin N1a.

In my original answer, I quoted the wavelengths of the Streuwellen as given in a 1945 Luftwaffe document summarising active and passive electronic aids.

To be specific, the document states of SN-2:

Streuwellen:
1. 2,37 m.
2. 2,46 m
3. 3.00 m
4. 3,30 m
5. 3,70 m
6. 4.10 m
7. 4,70 m

It is a simple procedure to convert wavelength to frequency (see the attached Gen.Nachrichtenführer table for example). According to the 1945 document, SN-2 had provision for seven Spot Frequencies between 63.8 MHz/4.70 m and 125.5 MHz/2.37 m. From other material, it seems Spot Frequencies IV to VI were in common usage in 1945. I have seen no evidence that Spot Frequency VII was used much, if at all.

Cheers

Rod

[CJE]

Many thanks, Rod.
That's quite clear now.

Chris