I don't know about the price end of it. But Jim's comment about the
alignment is true.
I fiddled around with some designs and then K8ZOA managed to talk me
into back into the land of sanity. Jack cooked up a version of his
filter which put one of the notches on the head of our local BC station
(I think it was on 1670). I was -60dBc there and -1 dBc at 1.80.
Unbelievable. Then again, Jack was the master.
Still you don't need to spend much time in front of a VNA to appreciate
the labor that can go into tweaking of some of these filters.
73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com
On 4/17/20 7:01 PM, Jim Brown wrote:
On 4/17/2020 4:19 PM, Roger Kennedy wrote:
> $180 for a receiver filter? That's absurd !
That depends on the design criteria. I don't know how it is in your
part of the world, but folks here who design and build stuff like to
get paid a living wage. A filter that passes 160M but strongly
attenuates 1710 kHz (sidebands of 1700 kHz) is not a simple one. It
requires a very good design and precision components, careful
manufacturing, and precision alignment.
(By the way, if you now have stations broadcasting between 1.6 and
1.7 MHz,
how does anyone pick them up? I don't know any broadcast radios that go
above 1.6 !)
This is one of those frequency allocations that varies by region. In
NA, the AM band, stations are assigned carrier frequencies from 540 to
1700 kHz, and radios sold here are programmed for that coverage. This
allocation has been in effect for several decades. By contrast, we
have no LF broadcasting.
73, Jim K9YC
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