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| From: | mleech |
| Subject: | Re: [Discuss-gnuradio] Probable pulsar observing success at CCERA |
| Date: | Thu, 01 Dec 2016 15:37:50 -0500 |
| User-agent: | Roundcube Webmail/1.1.5 |
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Yes, they are Digiwave ANT2084--available on-line through WalMart as it happens. But any similar 4-bay antenna will work. We use 6 of them in a 2 x 3 array. I was using a commercial combiner, but it was lossy and had poor phase balance (actually any hybrid-tree style combiner will have issues if the split ratio isn't a power of 2). I built my own transmission line combiner that combines all six in one go, transforming the 12.5 parallel impedance of all those lines into 50ohm for the LNA. Next time I build one, I shall use a slightly-different layout that will improve phase match a bit. One can, of course, calculate the line lengths required to effect any given pointing, but using matched-length lines from each module means that the beam is pretty much aligned with the mechanical axis. The LNA is prefixed with a pair of shorted-quarter-wave stubs, and it's a TQP3M9036, using the eval board available through DigiKey. But there are SPF5189Z LNAs on eBay at the moment for quite cheap that would do just as well. If you have an 8-10ft dish already, then use that. We went with the "modular" approach, since it allows us to increase antenna gain without taking down a dish and putting up a new one, and the HDTV antennae are fairly cheap, and readily available anywhere. They typically usefully cover about 300Mhz to 850MHz.
On 2016-12-01 15:19, Iain Young, G7III wrote:
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