Ku-Band LNBFs


The existence of inexpensive low-noise block downconverters (LNBF) for the satellite reception is fortunate as the bands they cover include the transition frequencies for two species of masers - the 12.178 GHz Methanol maser line and the 22.235 GHz Water maser line. However - the very reason why they are available means that reception of those maser lines can be subject to increasing levels of interference from those satellite signals.

The 'low-noise' part of LNBF refers to a low-noise front end amplifier (LNA) working at the sky frequency.

The 'down-converter' part of LNBF refers to a circuit which 'mixes' a local oscillator (LO) with the incoming sky frequency signal from the LNA - thereby 'down-converting' the sky frequency to a lower frequency - usually in the 1 to 2 GHz range.

This page deals with those Ku-band LNBFs which cover the 12.178 GHz Methanol maser transition line rest frequency.

Ku-Band LNBFs

Nomenclature for various satellite front-ends is a bit loose. Terms which mean one thing in one part of the world market can mean something else in another. Coupled with not uncommon errors in the specifications given by online sellers, it is very much a case of 'caveat emptor'. In some cases the true nature of the device advertised can only be determined by biting the bullet and ordering one to test. Fortunately they are not overly expensive - ranging from about USD$10 to somewhat less than USD$100.  Usually those experimenters who play with such devices have a bunch on hand - largely made up of units which were thought to be useful in their default state or after modification - only to turn out to be neither. I am looking at myself in the mirror as I write this...

Different Types Suitable for Methanol Masers

Generally speaking the 'F' in the term 'LNBF' refers to an integral feedhorn.  The electronics ride piggy-back on the waveguide-type feedhorn and upon feeding power - and some control signals - to the LNBF, the down-converted signal is available at one or more F-type female sockets mounted on the LNBF at a sufficient level to be transported to a receiver down a relatively inexpensive coaxial cable (75 ohm) run. These LNBFs come in a variety of configurations - but basically can be sub-divided into a number of types. The following is just commentary - as terms can differ with market region.

'Ideal' Ku-Band LNBF for Methanol Line Observation

The 'ideal' specification for Methanol line observation might be as shown on the right. It is a 'Standard' Ku-band LNBF, with a 10.750 GHz LO (PLL generated).

Other terms found: There are other terms used to describe variants to the above - including Twin, Dual, Quad, Octo, Monoblock and Quattro. These variants have different combinations with more than one IF output connectors and some have more than one waveguide feed on the same assembly. The only variant that might be of interest in radio astronomy applications would be a 'Standard' LNBF (preferably with a PLL LO @ 10.75 GHz) with two IF output connectors. In that case it would be possible to run two separate receiving channels - one with 'vertical' polarisation, the other with 'horizontal' polarisation. This would allow observing whether the maser line is linearly-polarised or not.

The LNBFs On-Hand

A total of 6 versions of Ku-Band LNBFs are on hand. Their details are shown below for reference. All are single output versions except for the Acer model (twin) and all are standard models (one band) except for the Bullseye model (universal - two bands).

LNBF Image Montage