IMD and 2.8 hz tx filter question

[KD8NNU]

Dear All,

Since I am contemplating adding the sub-receiver I will need matched
filters for diversity.

Currently I have the 2.7 Khz 5 pole and since filters need to be matched
I was thinking to go directly to the 2.8 8 pole filters.

So in addition to the matching for RX easily with no offset, will this
have any improvement in the TX IMD numbers.

Just curious.

Thanks

~73
Don
KD8NNU

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

[Jim Brown-10]

On 1/2/2012 6:54 AM, [hidden email] wrote:
> Since I am contemplating adding the sub-receiver I will need matched
> filters for diversity.

Diversity is most useful for weak signal reception, where narrower
filters are likely to be used. I would pay more attention to matching
those narrow filters.

73, Jim K9YC
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

[Bill W4ZV]

goldtr8 wrote

Dear All,

Since I am contemplating adding the sub-receiver I will need matched
filters for diversity.

Currently I have the 2.7 Khz 5 pole and since filters need to be matched
I was thinking to go directly to the 2.8 8 pole filters.

For unmatched 2.7k SSB filters, simply set both offsets to the average of the two (e.g. for -0.79 and -0.85, set both to -0.82).  You'll never notice 30 Hz shift in a ~2800 Hz filter (actual BW of 5-pole 2.7k) and you'll save $300.

RX IMD is not a real issue on SSB since TX IMD (i.e. splatter from SSB signals being received) is about 60 dB worse.  Even if it was, there's little difference in RX IMD performance between 5-pole and 8-pole filters (maybe 1-2 dB for narrow CW filters).

73,  Bill

[Barry N1EU]

Jim Brown-10 wrote

Diversity is most useful for weak signal reception, where narrower
filters are likely to be used.

Yes, diversity is an important tool for weak cw signal reception but it's also very useful/enjoyable to use regularly on ssb and a pair of 2.7Khz filters would work just fine for that.

73, Barry N1EU

[Guy, K2AV]

You will be surprised at the separation that diversity gets for noise
sources and voice.  The human brain (doing all the work in true diversity)
is an amazing thing.  If you can hold a conversation in a loud cafeteria
(remember high school?) your brain knows what to do.  The second full
capability RX in the K3 is a stellar and an extremely useful feature
feature.

Sometimes NB and NR muddle a weak signal in noise when diversity and both
NB and NR off allow my brain to sort it out.  Even if you are a die-hard
diversity skeptic, you owe it to yourself to go somewhere and hear it
yourself, just on the faint chance you are wrong  :>)

73, Guy.

On Tue, Jan 3, 2012 at 7:53 AM, Barry N1EU <[hidden email]> wrote:

>
> Jim Brown-10 wrote
> >
> > Diversity is most useful for weak signal reception, where narrower
> > filters are likely to be used.
> >
> Yes, diversity is an important tool for weak cw signal reception but it's
> also very useful/enjoyable to use regularly on ssb and a pair of 2.7Khz
> filters would work just fine for that.
>
> 73, Barry N1EU
>
>
> --
> View this message in context:
> http://elecraft.365791.n2.nabble.com/IMD-and-2-8-hz-tx-filter-question-tp7143986p7146626.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html