To: Paul Goldsmith

From: Jon Hagen

Date: Mar. 19, 1999

Subject: 430 Dual Beam Transmission

To provide a 430 beam from the Gregorian we need:

a. Installation of the slotted waveguide, including a matching device (tuner) at the transition between the regular waveguide and the slotted waveguide. On the carriage house side this tuner is a waveguide section with five stubs. We do not have another such tuner but I assume we can fabricate one. Felipe Soberal is providing a space for it in his design for the mechanical layout.

b. Installation of half-height waveguide from the traveling collector, through the collar truss, and down to the feed tower. We discussed the possibility of using large coaxial line but I'm convinced that the waveguide is preferable (no center conductor to suspend and connect). In addition, we won't need a matching device at the output of the collector, as its output is half-height waveguide.

c. Design and fabrication of bracketry to mount the spare collector on the Gregorian

d. Design and fabrication of a suitable compact turnstile junction. We have a spare turnstile for the 430 line feed. It is made of cast aluminum and is very heavy, being a structural element at the base of the line feed. I suggest we build a light-weight turnstile. As we discussed, it could have coaxial arms to make it more compact. But it may be possible to build a turnstile entirely in half- height waveguide. If so, we don't need to come up with a high-power coaxial-to-waveguide transition to make the transmitter connection. We would still need to make half-height waveguide-to-coax transitions for the receivers. This should pose no problem, as the half-height guide has half the impedance of ordinary guide and therefore is a much closer match to the coax.

(We'll have to find out what implication the reduced impedance of the half-height line has on the bandwidth of the turnstile).

HFSS may be of use in designing the turnstile, but I would suggest we build an S-band model (a comfortable size for development work). The Maple Ave. lab could make the model. Adjustments to the model would involve only the coaxial tuning probes; the model would not have to be sent back to Ithaca for modifications. We would also have to make up some half- height S-band waveguide sections, bends, and loads, as well as a half-height cal kit for the network analyzer. HFSS will at least be useful to estimate the power handling capability of a final design.

Jose' Maldonado can estimate the cost and labor involved in a. b. and c.

I estimate that the turnstile design would require perhaps 8 weeks after preparing the model and the associated S-band hardware. If experimentation shows that we need a full-height turnstile with coaxial arms, I would add another 8 weeks. Once we have settled on a design, I suggest we have it fabricated by an outside shop with large machines that can easily handle the full-scale 430 MHz device. We had trouble at Maple Ave. machining and welding the present 430 MHz OMT.