Sirius Radio antenna model ISGSRA733
The antenna that comes with Sirius and XM satellite receivers is an active device. DC power is supplied by the radio and fed via the coax to the LNA. These antennas have a 3 stage GaAsFET LNA with a ceramic band-pass filter - producing 35-40dB gain with a 0.5dB (35K) NF. The high gain overcomes the more than 20dB loss @2.3GHz of the long RG-174 coax cable that is supplied with the radio.
After 2 years my antenna became intermittent and then quit altogether. Based on how the new antenna works, I don't think the original unit ever worked properly. The new antenna produces a full-scale meter reading 95% of the time, no matter where I drive. In areas where the signal would drop out completely, the radio now receives programming, even though the level meter shows reduced signal.
Anyway, I thought I would fix the antenna for a spare, but couldn't really open up the unit without cutting away the plastic cover. Inside the unit there was lots of white crusty corrosion - obviously from condensation and the unit is not watertight. The coax enters through a hole in the metal mounting plate and connects to the LNA circuitry and there isn't any water proofing at this point. On my new antenna, I sealed around all the seams of the plastic housing with 3M RTV to keep the water out. Regardless, condensation will no doubt occur anyway.
Modification for 2304 MHz use
This unit would make a cheap LNA for 2.3 GHz with 0.5dB NF and new units are $30 on-line. As mentioned above, I opened the unit by cutting away the plastic top cover. The metal dome is the patch antenna. I applied just enough heat to the dome to melt the solder using a small torch - until it fell off the PCB.
If I can fix the LNA, I want to mount it in a brass housing with SMA connectors. Since the gain is so high, the output connection can be made with the RG-174. The input might take some work. More to follow.