[1000mp] Collins Filter and DSP

[Jim Smith]

I always find these filter discussions to be very interesting, 
particularly the different views people have of the same thing.

I just bought an Inrad 250 Hz to put in the sub-Rx because I find the 
Collins 500 Hz to be way too broad for me.   This is because I am trying 
to develop some SO2R skills by running on the Sub and tuning for mults 
on the Main.  With the 500 Hz filter in the sub there's so much racket 
going on that when someone responds to my CQ I am unable to get the call 
the first time and, if the signal is weak but readable, I can't get the 
call at all when the signal is being heard by only one ear.  I'm hoping 
that the drastically improved selectivity with the Inrad quartz will help.

The Collins is going into the Main and should eliminate the strong 
signal blowby in the 500 Hz position.

Can't report on how successful this is because I haven't done it yet.  
Maybe will have it done before CW Sprint.

73 de Jim Smith   VE7FO

Hans Remeeus wrote:

>Hello Ian,
>
>I agree with you.
>
>However it is rather difficult to compare the Main Rx with the Sub Rx,
>because the Main has three IF's, while the Sub has two IF's.
>
>Nevertheless the Yeasu YF-115C has very wide skirts, while the Inrad 400 Hz
>has very steep skirts. A noticable difference between these two filters!
>
>The YF-115C (or equivalent from Inrad) is good enough for the Sub Rx. IMHO
>it is even a very good choice for the Sub Rx, in the way you will use the
>Sub Rx...
>
>
>73, Hans Remeeus.
>Ham Radio: PA1HR
>www.remeeus.nl
>
>Communication is about people, the rest is technology.
>
>
>----- Original Message -----
>From: "Ian White, G3SEK" <G3SEK@ifwtech.co.uk>
>To: <1000mp@mailman.qth.net>
>Sent: Wednesday, January 28, 2004 9:45 PM
>Subject: Re: [1000mp] Collins Filter and DSP
>
>
>  
>
>>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.
>>
>>    
>>
>
>
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