There are 9 pages of rotary switches in the Mouser catalog that arrived
this morning. pages 1727 through 1735. A very suitable switch and box
could be had for a few bucks in a serial or parallel 1 to 4 switch box.
I used Collins packaged toroids in the first filter I built, and the
J.W. Miller chokes in the second one. While the Mouser catalog only
shows up to 100 mh, on line they show having 206 of the 220 mh in stock
and about 3200 of 100 mh from various vendors on hand.
RS has one similar but wrong transformer on line. MCM electronics has
the right one at a decent price:
http://www.mcmelectronics.com/product/555-7120
220 mh and 320 mh takes a lot of toroid winding. I'd rather do that by
machine than by hand, though I have would a toroid or two that size by hand.
I might have bought the transformers at RS, but more likely from some
mail order catalog like Hosfelt. The transformer is commonly used in
commercial PA systems yet.
73, Jerry, K0CQ
On 8/12/2010 4:44 PM, John Graves wrote:
> Jerry,
>
> That is a very interesting article. 10 years ago you could have bought
> most of the components at Radio Shack. I just had a quick look at the j.
> W. Miller line....Winding toroids seem to be the way to go now. Now to
> find that switch you used. Only commenting. What you have said makes
> sense to me (a network security person) My Dad was the mostly self
> taught audio guy (Thanks to WWII).
>
> John / WA1JG
>
> Dr. Gerald N. Johnson wrote:
>> One solution I use for really noise free audio is posted at:
>> http://www.geraldj.networkiowa.com/papers/speakerfilter.pdf This
>> filter has selectable cut off frequencies and being passive and built
>> for speaker impedance there is no high frequency noise introduced
>> after it by 100 KHz bandwidth audio output ICs.
>>
>> 73, Jerry, K0CQ
>>
>> On 8/12/2010 2:46 PM, Stuart Rohre wrote:
>>> Joe,
>>>
>>> You may want to read Rob Sherwood's web site on receiver and rig
>>> testing, about excess audio response. He reports operators get tired
>>> listening to any audio above the voice or SSB, needed frequencies.
>>> In fact, you may want to put a band limiting filter in front of any hi
>>> fi headphones to avoid operator fatigue if you do much DX operating.
>>>
>>> That has also been our finding at the Acoustics research lab where I
>>> work for the Navy sonar folks. Sonar operators need to only have the
>>> sonar frequency audible components and not a full span of ocean noise.
>>>
>>> 73,
>>> Stuart Rohre
>>> K5KVH
>>>
>>>
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