The Plumbing Defined Radio

The The Plumbing-Plumbing-

Defined Defined RadioRadio

Revisiting the Acoustic Wave Revisiting the Acoustic Wave FilterFilter

David Cripe NMØSDavid Cripe NMØS

FDIM 2011 - May 19, 2011FDIM 2011 - May 19, 2011

NMØS – THE PLUMBING DEFINED RADIONMØS – THE PLUMBING DEFINED RADIO

A top-coupled-resonator band-pass filter



•Advanced design for 1928Advanced design for 1928

•Predated lamb’s crystal filtersPredated lamb’s crystal filters

•Precision performance easily attainable in Precision performance easily attainable in home home workshop.workshop.

•No custom capacitors or inductors required.No custom capacitors or inductors required.

•No prior or subsequent mention of this No prior or subsequent mention of this technology in technology in QST!QST!

What was remarkable about this:

A clue:



Who was roland bourne, 1ana?

•Colleague and employee of h.p. maxim, at Colleague and employee of h.p. maxim, at maxim maxim silencerssilencers

•M.i.t. graduateM.i.t. graduate

•Frequent contributor to qstFrequent contributor to qst

•Pioneer in optical communication, rc flightPioneer in optical communication, rc flight

•Later, curator of arrl museum.Later, curator of arrl museum.

Acoustic science



Von helmholtzVon helmholtz


masonmason

Filter theory



HeavisideHeaviside

http://en.wikipedia.org/wiki/File:Line_model_Heaviside.svg


CampbellCampbell

http://upload.wikimedia.org/wikipedia/en/a/ac/Cambell_filter.png


BourneBourne

•Would have had access to Would have had access to bell labs journals and bell labs journals and latest research on latest research on acoustics and electric acoustics and electric filter theoryfilter theory

•W1ANA, understood need W1ANA, understood need for CW filteringfor CW filtering

•Successfully merged Successfully merged acoustics and filter acoustics and filter theorytheory

Acoustic-Electrical Analogues

• One Acoustic ohm:–The impedance required to produce

a pressure of one dyne/cm2 against a volume flow of 1 cm3 / sec



V0

Ca = _______

A2 × ρ

where:

V0 = volume of tubing, cm3

A = speed of sound of air, 34,000 cm/sec, and

= density of air, 1.2 mg/cmρ 3 at sea level.

Acoustic Capacitance


Acoustic inductance l × ρ

La = ________

S

where:

l = length of tubing, cm, and

S = cross-sectional area of tubing, cm2


Filter Dimensions

Equivalent circuit



Frequency response:

Impulse response of bourne’s filter:



What can be done?What can be done?

4-pole bessel filter


Physical implementation


Frequency response of improved filter


Impulse Response of Improved filter:



The future?The future?

•The modified Acoustic wave could supplement The modified Acoustic wave could supplement conventional cw filter methodsconventional cw filter methods

•PVC pipe could be used, much more easy to PVC pipe could be used, much more easy to work withwork with

•impedance of acoustic drivers and loads is impedance of acoustic drivers and loads is poorly understood – further research is poorly understood – further research is needed.needed.


questions?questions?

The Plumbing Defined Radio

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