Ben,

Don't confuse the 'unloaded' Q of the part with the 'loaded Q' of the
circuit.

The unloaded Q of the part is a measure of internal resistance in the part
and will mainly affect the loss of the network, not the bandwidth. The
loaded Q of the network is a measure of the external network resistance that
the part is embedded in and will mainly determine the bandwidth.
The ratio of unloaded Q to loaded Q will determine the losses of the network
(higher unloaded Q is better).

In general, high unloaded component Q is 'goodness'.

Joe
W3JDR


"Ben Jackson" wrote in message
...
In a coupling circuit such as:

C1|| C3||
IN----||----o----o----||--OUT
|| | | ||
--- C
--- C L1
C2| C
| |
'----'
|
===
GND

(see, eg, the "38 Special" NorCal 30m QRP tranceiver sch connecting
the NE602 single-ended output to an amplification stage:
http://www.amqrp.org/kits/38spcl/ )

What is the purpose maximizing the Q of L1 by using, say, a hand-
wound toroid vs a molded inductor? Rs of a 1.8uH moulded inductor
might be 1.5 ohms vs .1 ohm for 5 inches of 24ga wire. However the
expected effect in tank bandwidth doesn't seem to matter compared to
the large effect of varying C1 (very narrow for small C1, 5p in the
example).

I can see why a homebrewer would prefer to keep a bag of T37-2 and
some enamelled wire around, but in a kit such as that, wouldn't a
moulded inductor do just as well?

--
Ben Jackson AD7GD

http://www.ben.com/