--- In [email protected], "Eric Lemmon" <[EMAIL PROTECTED]>
wrote:
>
Most such duplexers are intended for splits of 5 MHz or
> greater.
True, probably most, but the subject comes up fairly often on the
list, as to whether a notch-only duplexer is suitable at a certain
site. The old DB4048, if I have the number right, is an example of a
VHF notch duplexer made for 600kc split. We have one in service on
one of our repeaters.
> Your comment that the additional pass cavity loss is nil, might be
overly
> optimistic. Truth be told, two pass cavities set for 0.5 dB IL are
> significantly better than one cavity at 1.0 dB. Lower IL means a much
> broader response.
Yup, understand. And I guess my comment about the IL being nil was
meant to be <relative>. .5 to 1.0db is probably tolerable, although
anything, especially on the receive side, is <too much>.
As I see it, the bottom line from this, is that a notch duplexer,
then, is not necessarily taboo, even at a busy site, because you can
always add pass cavities to tighten up if needed. And, at a dense RF
site, you may need to add selectivity even with a BpBr duplexer.
Laryn K8TVZ
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