[TenTec] INRAD Filter Question

[wlfuqu00@uky.edu (Bill L. Fuqua)]

Collins (Rockwell) was developing high speed adaptive modems 20 years ago. I 
think they understand filters better than you may think. But when it comes to 
the modulation techniques used in amateur radio filter phase , ripple and skirt 
just are not as important as some think. Much of the mythology still seems to 
still exist. I suppose next it will be suggested that we return to Gaussian 
filters like hams used in the 1920's. Well rounded and good phase response 
etc...

Impulse noise is convoluted by narrow filters from short high spikes to broad 
lower peaks. That is why noise blankers must be placed in a broadband IF of a 
receiver. If not it becomes almost ineffective as in the early the Drake 
transceivers.

        Other myths that are popular:

1. You must use acid flux when soldering surface mount components.
This one comes from the conversion from rosin to acid flux in the manufacturing 
industry.
The reason for this change was EPA and economy.  To clean rosin flux organic 
solvents are       needed. This generates a disposal problem of the waste. Acid 
flux may be cleaned with water  and  and a base is added to neutralize the acid 
so the water can sent down the drain.
For repair work or hobby work rosin flux is still the best. In many cases you 
don?t need to clean off the flux, it evaporates. But if you do just use common 
organic solvents. Alcohol or common dry cleaning fluid.

2. You must use lead free solder with surface mount components. 
This one goes along with the above. To send the waste water down the drain 
there must be no lead in it. So lead free solder is used. It also makes it 
easier to dispose of bad circuit boards and assemblies.  Lead-tin solder is 
still very good. Just wash you hands after using it. If you prefer using lead 
free solder do so because you are concerned about health issues not because ?it 
is what they use in industry?.
Also, the lead-fee solder always cools with a dull surface. That makes it 
difficult to determine if you have a cold solder joint or not.