Re: [loopantennas] Fewer turns in loop
- In a message dated 6/30/2006 10:51:51 AM Eastern Standard Time,
Since I only want to tune the upper
portion of the band, should I use fewer turns of wire and more
capacitance to achieve resonance at the selected frequency? If Q is
affected by the resistance of the wire in the loop, shouldn't fewer
turns result in higher Q?
Q is just one factor of a loop antenna. All else being equal I think more
turns on a loop provides more signal voltage for the same size antenna versus
fewer turns. Higher Q is not always wanted in a loop used for broadcast band
listening. If the Q is too high the tuning becomes critical and the bandwidth
will be narrow cutting off the higher audio frequencies leaving broadcast audio
sounding muffled and bassy. A number of high-performance loop antennas have a
switchable Q-killer built in for this reason. 73 Todd WD4NGG
- I'm not a electrical genius but it seem sto me that you should
optimize for a center frequency and use a standard 365pf capacitor. If
you have time to experiment by all means do so.. Start with more turns
and work your way down. There is no way to know the Q of the antenna
unless unless you have the test equipment. I got a post in my email
today asking about the dimensions for a 433Mhz loop. It qould be tiny
and what is up around that frequency?
--- In firstname.lastname@example.org, "Craig Cochran" <craig@...> wrote:
> I wrote in a previous post that I wanted to make a dedicated loop to
> receive one of my favorite stations on 1450 kHz.
> Since I want my system Q to be as high as possible, would it be better
> for me to use FEWER turns in my coil of wire and a larger capacitor
> than usual?
> In a 3 foot diameter loop that would tune the entire BCB I guess I
> would use approximately 8 turns of wire (the exact numbers are not
> important for my discussion). I would guess about 30-50 pf of the
> variable capacitor would be used. Since I only want to tune the upper
> portion of the band, should I use fewer turns of wire and more
> capacitance to achieve resonance at the selected frequency? If Q is
> affected by the resistance of the wire in the loop, shouldn't fewer
> turns result in higher Q?
> What would be the minimum number of turns I could use to maximise Q? Is
> there a resonable limit to the size of capacitor(s) I might use?
> Could someone enlighten my on this issue.