This is the point I was making. High spec coils Q of 1000's unloaded then
installed in a poor antenna system with poor Earth/Radials which degrades
the Q and influences bandwidth. What is the groundloss you mention at the
DK7FC site and overall efficiency.
----- Original Message -----
From: "Rik Strobbe" <[email protected]>
To: <[email protected]>
Sent: Sunday, December 18, 2011 5:01 PM
Subject: LF: RE: Re: Re: Re: Re: TX system at DK7FC, schematic
There is a difference between the coil Q (unloaded) and the antenna system
Q.
While the coil Q can indeed be > 1000 the antenna system Q will be much
lower due to groundloss.
As a fact it is mainly the groundloss that will determine the antenna
bandwidth.
73, Rik ON7YD - OR7T
________________________________________
Van: [email protected] [[email protected]]
namens mal hamilton [[email protected]]
Verzonden: zondag 18 december 2011 17:26
Aan: [email protected]
Onderwerp: LF: Re: Re: Re: Re: TX system at DK7FC, schematic
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
> >
> >
>
>
|
