The BBC: Licensed at public expense to spread lies.

=========================

And long may they be licensed at public expense.

But they sound more like the VOA than the VOA.

Error. My previous message was intended to be by private e-mail.
---
Reg

On Sat, 6 Mar 2004 14:06:58 +0000 (UTC), "Reg Edwards"
wrote:

I need a simple design for a BPF with a centre frequency of 17.2Mhz.,

============================

Hello Paul,

I'm not in the habit of fishing for compliments but, out of curiosity, did
you find my program BANDPAS1 of more use to you than the many other
responses to your query.

Thanks, Reg. See my reply to Mike (Active8) elsewhere on this thread.
I'm one of your biggest admirers and you've always been something of a
folk hero to me. :-)

By the way, the Pi-network filter can be matched to ANY pair of terminating
impedances by tapping down the coils at each end. Been there - done that.
It also allows the most convenient component values to be used.

Noted.
--

The BBC: Licensed at public expense to spread lies.

Paul Burridge wrote in message
...
Hi all,

I need a simple design for a BPF with a centre frequency of 17.2Mhz.,
corner frequencies one Meg or therabouts either side of that and a
reasonably good shape factor (nothing critical here). I don't mind
having to do a bit of tweaking of values myself if anyone has
something close to that they can post. Passive L/C combinations only,
please. (assume the usual 50R nominal Zs.)
Thanks,

p.
--

The BBC: Licensed at public expense to spread lies.


The simplest filter that'll get you by, is this one. (a couple of tuned
circuits with a bit of top-coupling :-) ...

___ ||C1
-|_R_¦------.----.-------||-------.----.-------, O/p
Source |L2 |C2 || |C2 |L2 |
I/p | | | | .-.
C| --- --- C| | |load R
C| --- --- C| |R|
C| | | C| '-'
| | | | |
=== === === === ===
GND GND GND GND GND

F1=16.2e6 'lower limit MHz
F2=18.2e6 'upper limit MHz
R=50 'Ohms source and load impedance
Pi=3.142

C1 = (F1+F2) / (4 x Pi x F1 x F2 x R)
C2 = F1 /(Pi x F2 x (F2-F1) x R)/2
L2 = 2xR /(4 x Pi) x (1/F1 - 1/F2)

The inductors end up being quite small but a couple of loops of wire cost
nothing. At 25megs the output is down to about 3% , which is not bad.

This particular style is the "3 element" design and from the traditional
"Constant K" filter stable. The pleasantly simple to design "constant K's"
and associated "M derived" filters, can be easily and freely used for most
day-to-day electronics work.

Exact Filter design, or 'synthesis' as they nowadays prefer to call it, can
be a nightmare if you're coming in from scratch. Even using a filter design
programme requires a good knowledge of filter types/performance/spec's
before data can begin to be entered.
If not using a prog' you move onto the more vexing method of having to
design an initial (prototype) low-pass filter, either via precalculated
tables or computing the required co-efficients, then mathematically
transforming the low-pass values into a bandpass (etc) design. For higher
order filters it can be ball-acheing drudgery and even then inductor
resistance has a nasty habit of spoiling that pristine work of art. (not a
problem with DSP filters).

I can't suggest a decent book, as the general purpose books seem over
complicated and destined to be written by maths people for maths people.
(The old GPO line-comm's manuals have useful notes on the 'K and M '
filters).
regards
john

Go to Alt Binaries Schematics -
bg
Paul Burridge wrote in message
...
Hi all,

I need a simple design for a BPF with a centre frequency of 17.2Mhz.,

On Thu, 04 Mar 2004 23:43:21 +0000, Paul Burridge
wrote:

Hi all,

I need a simple design for a BPF with a centre frequency of 17.2Mhz.,
corner frequencies one Meg or therabouts either side of that and a
reasonably good shape factor (nothing critical here). I don't mind
having to do a bit of tweaking of values myself if anyone has
something close to that they can post. Passive L/C combinations only,
please. (assume the usual 50R nominal Zs.)
Thanks,

Since your too lazy to do this, here, have a few designs. You can run
these on LTSpice. What is reasonably good shape factor?
Mark

Butterworth, pi-input, 1st-order low-pass prototype
Vin 1 0 AC 2.0000V
Rin 1 2 50.000
L1 2 0 26.899n
C1 2 0 3.1831n
Rout 2 0 50.000
..AC DEC 396 253.58kHz 1.1667GHz
..PROBE
..END

Butterworth, pi-input, 2nd-order low-pass prototype
Vin 1 0 AC 2.0000V
Rin 1 2 50.000
L1 2 0 38.041n
C1 2 0 2.2508n
L2 2 3 5.6270u
C2 3 4 15.216p
Rout 4 0 50.000
..AC DEC 792 5.7378MegHz 51.560MegHz
..PROBE
..END

Butterworth, loose coupled, 2nd-order low-pass prototype
Vin 1 0 AC 2.0000V
Rin 1 2 50.000
C1 2 0 2.0654nF
L1 2 0 38.046nH
C2 2 3 185.01pF
C3 3 0 2.0654nF
L2 3 0 38.046nH
Rout 3 0 50.000
..AC DEC 792 5.7378MegHz 51.560MegHz
..PROBE
..END

Butterworth, pi-input, 3rd-order low-pass prototype
Vin 1 0 AC 2.0000V
Rin 1 2 50.000
L1 2 0 53.798n
C1 2 0 1.5915n
L2 2 3 7.9577u
C2 3 4 10.760p
L3 4 0 53.798n
C3 4 0 1.5915n
Rout 4 0 50.000
..AC DEC 1188 10.224MegHz 28.937MegHz
..PROBE
..END

Butterworth, loose coupled, 3rd-order low-pass prototype
Vin 1 0 AC 2.0000V
Rin 1 2 50.000
C1 2 0 1.4607nF
L1 2 0 53.798nH
C2 2 3 130.84pF
C3 3 0 1.3299nF
L2 3 0 53.798nH
C4 3 4 130.84pF
C5 4 0 1.4607nF
L3 4 0 53.798nH
Rout 4 0 50.000
..AC DEC 1188 10.224MegHz 28.937MegHz
..PROBE
..END

Butterworth, loose coupled, 8th-order low-pass prototype
Vin 1 0 AC 2.0000V
Rin 1 2 50.000
C1 2 0 511.07pF
L1 2 0 137.94nH
C2 2 3 109.63pF
C3 3 0 457.95pF
L2 3 0 137.94nH
C4 3 4 53.121pF
C5 4 0 527.60pF
L3 4 0 137.94nH
C6 4 5 39.985pF
C7 5 0 543.91pF
L4 5 0 137.94nH
C8 5 6 36.809pF
C9 6 0 543.91pF
L5 6 0 137.94nH
C10 6 7 39.985pF
C11 7 0 527.60pF
L6 7 0 137.94nH
C12 7 8 53.121pF
C13 8 0 457.95pF
L7 8 0 137.94nH
C14 8 9 109.63pF
C15 9 0 511.07pF
L8 9 0 137.94nH
Rout 9 0 50.000
..AC DEC 3170 15.208MegHz 19.453MegHz
..PROBE
..END

I need a simple design for a BPF with a centre frequency of 17.2Mhz.,

============================

Hello Paul,

I'm not in the habit of fishing for compliments but, out of curiosity, did
you find my program BANDPAS1 of more use to you than the many other
responses to your query.

By the way, the Pi-network filter can be matched to ANY pair of terminating
impedances by tapping down the coils at each end. Been there - done that.
It also allows the most convenient component values to be used.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........