Sawbird Bandpass Plots...
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Steve Olney
Mar 19, 2023, 8:56:21 PM3/19/23
to Society of Amateur Radio Astronomers
Hi All,
I know the +HI plot has already been shown here - but I am not sure about the other two I have on hand - +IR and +GOES.
In case it might be of use some plots can be found here...
Comments/corrections/criticisms welcome as always.
Cheers
Steve Olney
(HawkRAO)
Marcus D. Leech
Mar 19, 2023, 9:07:25 PM3/19/23
to sara...@googlegroups.com
Thanks for doing these tests and sharing the resulting plots.
I'll note that the SAWBird LNAs have generally been designed using *already available* SAW filters that happen to
"straddle" the bands of interest--this is particularly the case for the +H1 LNA, where they used a filter that's designed
for another application but happens to adequately "cover" H1. Which is why it's about 65MHz wide, rather than the
27MHz notional bandwidth of the radio astronomy band. Had they had custom SAW filters made, the "street" price of
these devices would be considerably higher...
In practice, this seems to be fine, although we "augmented" our filtering at the CCERA observatory with a wideband (200MHz),
low-loss filter custom built for us by PE1RKI, and placed (horror-of-horrors) IN FRONT of our SawBird LNAs.
The main concern for us was the cell-site less than 1 km from the observatory with fairly-strong 700MHz transmitters that
could conceivably de-sense the 1st stage. Praise be to whatever gods one praises for such things, the 700MHz frequency
plan around here avoids situations where the 2nd harmonic can fall into the radio astronomy band.
I'll note that the SAWBird LNAs have generally been designed using *already available* SAW filters that happen to
"straddle" the bands of interest--this is particularly the case for the +H1 LNA, where they used a filter that's designed
for another application but happens to adequately "cover" H1. Which is why it's about 65MHz wide, rather than the
27MHz notional bandwidth of the radio astronomy band. Had they had custom SAW filters made, the "street" price of
these devices would be considerably higher...
In practice, this seems to be fine, although we "augmented" our filtering at the CCERA observatory with a wideband (200MHz),
low-loss filter custom built for us by PE1RKI, and placed (horror-of-horrors) IN FRONT of our SawBird LNAs.
The main concern for us was the cell-site less than 1 km from the observatory with fairly-strong 700MHz transmitters that
could conceivably de-sense the 1st stage. Praise be to whatever gods one praises for such things, the 700MHz frequency
plan around here avoids situations where the 2nd harmonic can fall into the radio astronomy band.
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Marcus D. Leech
Mar 19, 2023, 11:19:03 PM3/19/23
to sara...@googlegroups.com
On 19/03/2023 20:56, Steve Olney wrote:
I believe that the filter that's being used for +H1 is:
https://www.taisaw.com/upload/product/TA1077A%20_Rev.1.0_.pdf
https://www.taisaw.com/upload/product/TA1077A%20_Rev.1.0_.pdf
Steve Olney
Mar 20, 2023, 6:20:11 PM3/20/23
to Society of Amateur Radio Astronomers
See later post for URL change...
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