[Yaesu] Filter Improvements for FT-1000D

[Ed Senior]

Hi again, Joe - 

I would like to thank you again for taking the time to comment 
on this topic.  I have found it quite interesting and enlightening! 

In the quotes below, I have snipped one of the "closed" subtopics, 
and added comments to the others... 

73, Ed, W6LOL

----- Original Message ----- 
From: "Joe Subich, K4IK" <k4ik at arrl.net>
To: "'Ed Senior'" <eseniors at earthlink.net>; <yaesu at mailman.qth.net>
Sent: Monday, May 09, 2005 1:27 PM
Subject: RE: [Yaesu] Filter Improvements for FT-1000D
> 
> Ed, 
> 
> > > > > 2800 Hz Inrad instead of the standard 2400 Hz Yaesu
> > > > > 2100 Hz Inrad as optional SSB
> > > > 
> > > > I take it you prefer leaning a bit more towards "high
> > > > fidelity" audio, vs. maximizing selectivity.
> > > 
> > > Yes, Hans likes the higher fidelity audio on SSB <G>.  Based 
> > > on their part number, each of the Yaesu filters (8.215 MHz and 
> > > 455 KHz) are actually 2600 Hz wide at the -6 dB points.  When 
> > > cascaded, they yield 2400 Hz overall at the -6 dB points. 
> > > 
> > That all makes sense, and I don't see much wrong with it if they 
> > are good filters.  But specifying BW at the 6dB points is kind of 
> > nonstandard, and I can see why some might want a little more BW. 
> 
> It is standard to specify bandwidth at the - 6 dB points.  When  
> any two filers of similar bandwidth are cascaded, the effective 
> bandwidth is somewhat less than a single filter alone.  

I am aware of the bandwidth shrinkage resulting from cascaded 
filters.  But it looks like we need to go to the next level of detail 
re "standard" definitions of bandwidth.  

I see that Inrad does indeed specify their filter bandwidths in terms 
of 6 dB points--so for Inrad, that is "standard."  And it could be 
that some other vendors of HF comm filters do the same thing.  
This is probably what you had in mind with your comment above.  

But this definition is NOT "standard" in the broader world of RF 
engineering.  In that world, 3 dB bandwidths are "standard," and 
there are good reasons for it.  One reason is that the 3 dB BW is 
very close to the noise power BW for most filters, thus making 
system SNR calculations relatively simple and easy.  

As an example, I note that virtually all of Chapter 16 ("Filters 
and Projects") in the ARRL handbook uses 3 dB bandwidths.  
The only reference to 6 dB points I see in that chapter relates to 
the popular 60 dB/6 dB definition of shape factor.  (And if I didn't 
have my RF engineering references all packed away, I'm sure 
I could come up with weightier tomes showing the same usage.)    

None of this is a problem, as long as everyone is clear about the 
definition being used in a particular situation.  Inrad uses 6 dB. 
I don't have to like it, but now that I know, I can easily live with it.  
8-)  
 
--------------
> <snip> 
--------------

> > > BTW, the INRAD web site indicates the FT-1000D roofing filter 
> > > is available (delivery at Dayton).  Based on the results in my 
> > > Mark V, I would make a roofing filter the first filter addition 
> > > to an FT-1000/FT-1000D.  
> > > 
> > Now this sounds interesting.  But would this be a hack-type 
> > modification, or does the 1000D have an available "slot" for 
> > a roofing filter?  
> 
> It's not particularly a "hack."  The roofing filter and post 
> amplifier is designed to mount in an empty space on the chassis. 
> Two wires are run to an adjacent circuit board for 5 volts and 
> ground.  One coax is unplugged from the circuit board and moved 
> to the roofing filter and a coax jumper is connected between 
> the roofing filter board and IF board. 
> 
Thanks for this info.  I also looked this up on the Inrad site.  

I must confess I have a strong preference for "no-solder" mods--
not because I'm afraid of soldering, but because I like being 
able to revert seamlessly back to stock, should it be necessary. 

Do you happen to know the bandwidth and/or filter type of the 
standard FT-1000D "roofing" filter--if it has one?  

--------------

> > > 2) INRAD 400 Hz CW filter for the sub receiver 
> > 
> > If one replaced the Main Rx 500 Hz filter with one of these, 
> > could the standard filter from the Main be trickled down to 
> > this spot in the Sub?  
> 
> No, the center frequencies are different (455.0 KHz for the 
> main vs. 455.7 KHz for the sub-receiver). 
> 
Thanks, I would not have known that unless I combed through 
the technical manual!  

----------------

> > Also, if one wanted to minimize "unauthorized" mod's, couldn't 
> > one just add another standard 500 Hz filter to the (presumably 
> > open) "slot" in the Sub?  
> 
> Not a "standard" main receiver filter - the center frequencies 
> and physical shape are different.  However, INRAD has a 500 Hz 
> filter that is a drop in replacement for the Yaesu XF-455MC 600 
> Hz filter. 
> 
And what is the Yaesu XF-455MC 600?  Is that a filter that 
Yaesu offered as an option for the Sub Rx?  And if it was, 
is there anything wrong with using that?  

---------------

> > > 3) replace the Murata ceramic filter in the sub-receiver 
> > >    with an INRAD 702 
> > 
> > That would be nice.  Would another of the original Yaesu 
> > XTAL filters (same as the Main) be another option? 
> 
> Yes, if one can find the Yaesu 2.6 KHz (XF-455K-262-01) filters. 
> Another option might be a 10 pole Collins 2.4 KHz filter from 
> INRAD (717). 
> 
As above, what is the Yaesu XF-455K-262-01?  Is that (also) 
a filter that Yaesu offered as an option for the Sub Rx?  

And another question:  Do you know why Inrad does not show 
anything except CW filters available for the FT-1000 Sub Rx 
on their website chart?  (The 702-C is listed only as an option 
for the Main Rx.) 

And yet another question (I'm just full of 'em):  Can you tell me 
what Inrad means when they say "Filter Fits By: Custom PC 
Board?"  Does that translate to plug-in, drop-in-and-solder, 
or solder-in flying leads, in the case of an FT-1000D?  

If you want to point out that you're not flipping Inrad Sales or 
Tech Support for at this point, I'll understand!  ;-)  

----------------

> > > 4) add the optional 250 Hz 3rd IF filter if necessary.
> > 
> > Would the benefit of this simply be that selecting a 250 BW 
> > would also give that BW in the Sub, instead of the Sub 
> > just staying at 400/500 Hz?    
> 
> No, the 250 Hz bandwidth is available only in the main receiver 
> unless one chooses to 'wire in' a 250 Hz filter as the only 
> CW filter in the sub-receiver (the sub-receiver supports only 
> one CW filter).   
> 
Again thanks for very useful info!  This tidbit might be in the 
manual, but I hadn't noticed it.  

----------------

> 73, 
> 
>    ... Joe, K4IK 
>  
> 
> 
>