Duane,
My buddy abruptly stopped working on that project. He apparently got busy
with too many irons in too many fires. He wasn?t planning on using an
attenuator, just more modules. :-) I don?t know when he will return to his
work on it. I believe he had all the stuff for a 4 module unit. He was
also modifying four Sweet 16 CB amps in a stack for ham radio, he had to
retransform them... I don?t know where he got there either. Everything is
stalled.
W8ZR's easy tuner is a very nice box. Way deluxe.
Just add a 4 module EB-104 setup ahead of it and you've got a nice all band
KW for home or office.
I've only built resistor attenuators here and that was 20 years ago. I've
had no need since. I had to drop 200 watts to less than 3. That was a mess
of resistors. There was an article about passive attenuators in QST I had
from either the late 60's or 70's. It was the cover article. Had all the
formulas.
BØB DD
-----Original Message-----
From: Duane B [mailto:d-brantley@sbcglobal.net]
Sent: Monday, December 04, 2006 11:13 AM
To: Robert B. Bonner
Cc: amps@contesting.com
Subject: Re: [Amps] Low Pass Filters
Hello Bob,
Would something like this fit the bill?
http://www.w8zr.net/eztuner/index.htm
Also, your friend that is building the EB1-4 600W SS Amps, what is he
doing for an attenuator for the input? As designed, 10 ~ 15 in will get
the full 600W out. In the 2006 ARRL Handbook, they mention a
"frequency-selective attenuator", p 18.25. This sounds like a good idea,
given the fact that the gain is higher as 2MHz than at 30MHz. Would you,
or anyone for that matter, know how to build this type of attenuator, or
could refer me to some info on them?
Thanks,
Duane
Robert B. Bonner wrote:
> Tony,
>
> The problem isn?t going to be so much the voltage as the current.
>
> The impedance of the filter is going to be 50 ohms. That alone will keep
> the voltage under tow. The current through the filter however will be
> substantial. If the actual power is 600 watts average and average = PEP
> then your antenna current should be 3.46 amps and the voltage should stay
> below 200 volts. (175)
>
> I'd build the unit for more current capability (4-5) to gain some safety
> factor and if you were to use 500 or 1000 volt mica caps in parallel to
get
> your current capability you would have a safety factor there.
>
> SWR is your enemy. Once the reactance of the antenna goes out of line you
> will have either higher currents or voltages present themselves to the
> output of the filter. This could set you up for a failure.
>
> Now here's a better idea and I've been thinking this is what the guys at
> like Icom and Yaesu were thinking with the PW-1, IC4KL and Quadra...
>
> Why not build a multiple section auto antenna tuner to go at the output of
> the amplifier?
>
> The tuner will straighten out antenna SWR shown to the amplifier, plus it
> would also act as your bandpass filter...
>
> A 5-7 pole Chebycheff filter has considerable attenuation of harmonics,
but
> so would an adjustable PI filter at the output. You could do a combination
> of a standard bandpass filter with the addition of the load matcher.
>
> You kill both birds with the one unit.
>
> If you built it EXTRA BEEFY You could attach it to ANY amplifier via
coax.
> SO say you decided, hey its time to build a 4KW solid state amp, well hey
my
> bandpass filter and tuner were designed correct up front. Or say hey this
> 600 watter works great, let's add another module for 1200 watts!
>
> You would want to limit power to the filter until the load is tuned
somehow.
>
> If this is for only mobile use? Three things. Well then size the output
> for the maximum you would need. Since you don?t have a device with 3000
> ohms (tube) you don?t need the super mega 15 KV components. Also the
> amplifier and bandpass do not need to be located together. They could
> interconnect with a coax and control cable easing mounting or location
> selection in a mobile environment.
>
> With a mobile I'm not convinced you even need a filter... The bandwidth
of
> a mobile antenna is sharp. I feel it itself works as a filter and
> attenuates harmonics and radiation. Sure some of it is going to get out,
> but more likely it will be reflected back at the amplifier and need to be
> dissipated as heat in the final. MEASURE harmonic output and see how much
> you are really talking about. You are constantly driving away from your
> problems.
>
> There is no way I'd ever do that with a home install.
>
> BØB DD
>
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of ANTHONY JAPHA
> Sent: Sunday, December 03, 2006 2:43 PM
> To: amps@contesting.com
> Subject: [Amps] Low Pass Filters
>
> Greetings all,
> What voltage rating should be used for the caps in low pass filters
> following a 600 watt solid state amp? How about a KW amp? The LPFs are 5
> or 7 pole Chebycheff designs just like the Handbook filters.
>
> Many thanks for any advice.
>
> 73,
> Tony, N2UN
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>
>
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|