? Load Capacitance For 160 M

[WD4TC]

 After looking at my output circuit for 160 meters and doing some calculating I got to wondering How much Cap. should it take to load a pair of 833 on 160 meter ?? I think there was about 5,000mmf  on my RCA BTA 1 MX when I got it and it was suppose to be on 1885. Appox how much should there be For a PI 
 network for 1885??  Thanks Tim...WD4TC...

[n2bc]

Hi Tim,  PI network calculator here:

http://my.athenet.net/~multiplx/cgi-bin/pinet.main.cgi

You need to know anode I and E and desired tank Q 

[WA1GFZ]

Tank Q of about 12 is a good number. I suspect a bit lower than 5000 pf.
higher C means higher Q and circulating current.

[W3SLK]

Frank said:

Tank Q of about 12 is a good number. I suspect a bit lower than 5000 pf.
higher C means higher Q and circulating current.

Weren't the Q's for broadcast box slightly lower than 12? I seem to remember it being stated as 10 to accomodate the broader audio bandwidth.

[Steve - WB3HUZ]

Some may have been, especially at the lower freqs. But for amateur service, 12 is a good number for efficiency and harmonic suppression.

Bandwidth is related to Q as follows

BW = f/Q

So for 1.9 MHz you are looking at a bandwidth of over 150 kHz. This should be enough for sufficient highs on the audio. ;-)

Frank said:

Tank Q of about 12 is a good number. I suspect a bit lower than 5000 pf.
higher C means higher Q and circulating current.

Weren't the Q's for broadcast box slightly lower than 12? I seem to remember it being stated as 10 to accomodate the broader audio bandwidth.

[WA1GFZ]

Broadcash finals could run at lower Qs because the antenna interface is selective.
Phasing components and matching components reduced harmonic emissions, Ham transmitters that feed an antenna with coax have no additional harmonic filtering so the tank needs to do the whole job.
An antenna tuner helps. 

[WD4TC]

  Thanks Men for all the replies and info..I was just looking at it as it were, and the way I got it Now on 160 and I was thinking of trying to move it to 3.725.With the calculator and input I have gotten I don't see why it would not go OK . Assuming I got the Load resistance correct for Parallel output of the 833's I think that for 160 it should go L=18.5Uh  C-1 =425  C-2=2420 and for 80 meter about 1/2 that,. I suppose I just do it and see what happens. Worse case it just to put it back the way it is Now...Just can't leave it along....
                                       I just got to know !     

[WA1GFZ]

Tune the rig up on the bottom of the band and check efficiency then tune up at the high end and check efficiency. If it works better at the low end then you have extra L. If it works better at the high end then you could add some.
You are right on the money if the efficiency is equal.
if you really want to dial it in....

less L means more circulating current in the inductor so it has to be able to handle the current. The rig should work fine with a Q 10 to 15 if the components can handle the power.