[1000mp] Collins Filter and DSP

[Ian White, G3SEK]

>Re: the Collins Filter in the sub RX. It only works properly if 
>installed one
>way. When I first put it into my Field sux RX, it did not work. So I 
>reversed it and it worked fine. So make sure that you set the menu to 
>turn it on and check it before you put the cover back on. Subsequently, 
>I replaced the Collins with an INRAD 400 Hz filter in the sub RX. I 
>like it a lot better.


I found the same. Compared with the two cascaded 500Hz filters in the 
main RX, the single Collins 500Hz filter in the sub-RX sounded waaay too 
broad. The skirts just didn't drop away fast enough. Some off-tune 
signals were so strong, I sometimes had to check that the sub-RX hadn't 
flipped back to the SSB filter.

The Inrad 721 500Hz filter made an amazing difference in the sub-RX. 
When signals are outside the passband, they're pretty much gone. 
Comparing the data for the two filters shows why: signals that are 600Hz 
off-tune are 30dB stronger through the skirts of the Collins filter than 
they are through the skirts of the Inrad.... and that's a lot.

If you think about the extra cost of the Inrad filter, and then factor 
in the relatively small amount of time you actually use the sub-RX, you 
could conclude that putting an Inrad in there is terrible value for 
money. Well, maybe... but it certainly makes a big difference!

Final point: the Collins 500Hz filter sounds great when it's cascaded 
behind the stock Yaesu 500Hz filter at 8.2MHz, and the combined skirt 
performance is very acceptable. Of all the available CW filter 
combinations in my (old-style) MP, those two are my favorite to listen 
to.



-- 
73 from Ian G3SEK