# S-Band

At S-Band, the majority of satellite downlinks fall in the 2.2GHz to 2.3GHz band - there are exceptions to this as always. This band is specifically reserved for Space to Earth transmission of TT&C, ranging data and payload data. Most of the traffic could be described as uninteresting, as its either CW, PSK or spread spectrum, but there are some fantastic opportunities to perform some Doppler analysis in order to determine the satellite and it's orbit. The majority of S-Band downlinks are RHCP.

The frequency charts below show results from investigations of what can be heard at S-Band - this list is the most comprehensive 'open source' list of S-Band downlink frequencies published. Most US satellites operate in the standard SGLS channels, frequency details of which can be found below, whilst non-US satellites generally have a varied band plan. Sven Grahn from Sweden has written an excellent page about his S-Band adventures, you can read about them here. Michael Fletcher from Finland has written up his s-band experiments with the JAXA / Selene moon orbiter, here.

For most of the loggings on this page, a 88cm dish, 3.5 turn S-Band helical feed and a G4DDK vLNA were used.

The frequencies listed below are actual 'off air' frequencies as received, and not guessed centre frequencies based on perceived Doppler shift. S-Band sky survey: xBr, Freq, pjm, Greg, Trango, Lem and #hearsat members. Note: All frequencies listed have been verified.

Frequency tables sorted by Satellite Catalogue Number then Frequency:

Frequency table sorted by Frequency:

Helix Antenna

A simple 3.5 turn LHCP helical antenna centred on 2250MHz is described below; this feed can be used with prime focus or offset dishes. It is possible to wind this antenna in the opposite sense (i.e. RHCP) to use as an S-Band omni in order to monitor LEO and HEO satellites. The dimensions for the helical are not overly critical, but should be within a couple of mm of those quoted. The ground plane can be made from double sided PCB or aluminium, and it is recommended that a SMA or N-Type connector is used. The helix element can be made of 1.5mm or 2mm copper wire; the prototype used 2mm silver plated copper wire. The helix element can be made self supporting, but it is better practice to make a supporting rod from nylon or plastic. The first quarter turn of the helical should be spaced 2mm from the ground plane when using 2mm wire for the helix element for impedance matching purposes. It is worth experimenting with the matching by soldering a copper strip to the first quarter turn in an attempt to improve the match. Another alternative is to mount a metal block on the ground plane that can be adjusted near to the helix element to improve the match. Work is progressing to assess the suitability of Sirius / XM active S-Band antennas for satellite DX'ing purposes.

A couple of examples of home-brew S-Band antennas are shown below, on the left is a QFH omni, and on the right a wide beamwidth helical suitable for use as an omni.

QFH Antenna

Another omni directional antenna is pictured below and is a QFH as designed by Michael OH2AUE.

Low Noise Amplifiers

(above) Minikits VK5EME LNA tuned for 2250MHz

Noise figure plot for the above LNA:

(above) G4DDK LNA adjusted for 2250MHz centre frequency

The preamp pictured here is a super low noise design by G4DDK with a measured noise figure of 0.30 - 0.33dB and 25 - 26dB associated gain at 2.3GHz.

The G4DDK LNA is currently under test on S-Band, but initial results appear to suggest that it delivers a worthwhile increase in SNR over the MiniKits LNA. The G4DDK LNA is supplied as a kit of parts which should take around 2 hours to build for an experienced constructor.

This LNA runs from a seperate +12V supply which is split out from the RF path using a mini-circuits wideband bias-T.

(above) LNA4ALL broadband LNA - great performance on S-Band

This LNA is the LNA4ALL and has been designed by Adam 9A4QV and is based on the PSA4-5043+ MMIC from Mini-Circuits. The LNA has around a 1dB NF at 2.2GHz and an associated gain of 13dB gain, making it suitable for use as a front end LNA. Noise figure results from actual testing are shown below: