Certainly not. What Stefan meant was the coil's *unloaded* Q, which
cannot be high enough.
The *loaded* Q, in the resonant circuit, will be lower and that's what
determines the antenna system's bandwidth.
Cheers,
Wolf .
Am 18.12.2011 17:26, schrieb mal hamilton:
ps
With a Q in thousands the bandwidth even on 137 would be too narrow to be
useful
----- Original Message -----
From: "mal hamilton"<[email protected]>
To:<[email protected]>
Sent: Sunday, December 18, 2011 4:02 PM
Subject: LF: Re: Re: Re: TX system at DK7FC, schematic
Jim es Co
The highest Q coils I have seen are self supporting encased in a helium
container and the Q specified was only in a few hundred. What sort of coil
construction yields 4000 and above ?
I have yet to encounter such a specimen
mal/g3kev
----- Original Message -----
From: "James Moritz"<[email protected]>
To:<[email protected]>
Sent: Sunday, December 18, 2011 10:58 AM
Subject: LF: Re: Re: TX system at DK7FC, schematic
Dear Mal, LF Group,
I can see you resonate your 3mH coild with a motor driven variometer
but
how
do you match this to exactly 50 ohmz for a SWR of 1:1 to the TX
I can see your coil and transformer secondary are in series to earth
but
no
adjustment for matching.
Essentially the same arrangement is in use here. The transformer ratio
is
adjusted to match the antenna resistance to 50ohms.
A Q of 1000 is typical for a coil of this size wound using Litz wire.
You
might increase that somewhat by optimising length, diameter, winding
pitch
etc. For something big like the Balboa loading coil in Alex's mail, Q
can
be
considerably higher - Watt's "VLF Engineering" has data on this
particular
antenna system - the coil resistance at 25kHz is about 0.06ohms, and the
reactance 225ohms, making the Q about 3800 - it might be higher at 136k,
since reactance often increases faster than loss resistance as the
frequency
goes up. Incidentally, I estimate L of the main loading coil about
1.3mH,
so
GW0EZY would need the variometer in series as well ;-)
Cheers, Jim Moritz
73 de M0BMU
|
