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RE: Primestar 1m dish on 435 mhz



> I recently acquired a Primestar 1 meter dish and am considering it for a
> helix feed on the 435 uplink. Has anyone tried this or have any comments?


Adding to others' comments, (eg a 4 ele yagi is smaller and has more gain at
70cm) I had difficulty feeding a 1.2m dish at 70cm for the following
reasons:

(a)	dish itself severely detunes 70cm feed especially at low f/D's. Despite
a number of attempts, I couldn't get a variety of simple dipole/reflector
feeds to tune in with a low VSWR.

(b)	If a helix feed is used, the feed itself can shadow a very significant
part of the dish area, even on an offset fed dish

(c)	your downlink will suffer lots of desense if you use the same dish
unless careful attention is paid to filtering. I have  managed to blow
preamps/downconverters because of the high 70cm RF.

My compromise for a 'dual band' antenna is shown at
http://www.g6lvb.com/brollydish2.htm where either a reflector/dipole or
helix 2.4GHz feed can be used at the focal point of the dish, and a 70cm 4+4
ele CP yagi points the other way but is also attached to the 'feed arm'.

73 Howard G6LVB

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