[ICOM] Re: ICOM IC-775 Roofing Filter

Mon Jun 11 15:49:58 EDT 2007

Hi Anders,

I have written a short Web article on filter matching in analogue Icom
radios fitted with PBT or Twin PBT.

http://www.ab4oj.com/icom/xfilter.html 

The best pairing for 2.4 kHz SSB is FL-80/FL-44A or FL-80/Inrad 109. For
narrow SSB, the FL-223/222 is best; Inrad has a drop-in equivalent for the
FL-222 455 kHz filter. 

The FL-100/FL-52A and FL-101/FL-53A are best for 500 and 250 Hz CW
respectively. Again, Inrad has equivalents for the FL-52A and FL-53A. In
general, I  recommend the Icom 9 MHz filters, as they are drop-in and coax
jumpers (with their attendant blow-by risk) are not required.

As you said, the roofing filter is a separate issue from the IF selectivity
filters.

Cheers for now, 73,
Adam VA7OJ/AB4OJ

-----Original Message-----
From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net] On
Behalf Of Anders Janis SM4RNA
Sent: Monday, June 11, 2007 12:30
To: Skip Cameron; ICOM Reflector
Subject: [ICOM] Re: ICOM IC-775 Roofing Filter

The roofing filter is not be confused with non roofing filters in the 9M and
445k. (only Ten-Tec'ers do that!)

The 9M and 445k filters are for nerby action and actual bandwith selection. 
The roofing filter improves the actual receiver preformance by letting less
amount of signals in to the mixers, switching diodes, NB-circiut or what
ever.

As in your question you state that 2,4kHz is to wide the 9M and 455k filters
is what you need. The roofing filter is around 5kHz wide and has nothing to
do with close in selectivity to do. I my self, have and I can recomend the
Inrad roofing filter but it do not do what you want to acomplish.

The best improvement when it comes to real selectivity on SSB, I find it to
be when changing the FL-96 2,7kHz, yes it is 2.7kHz (chek manual and or
service manual and www.mods.dk) in the 455kHz IF to a Inrad #109 2,4kHz. It
is choosen together with the FL-80 2,4kHz filter in 9MHz IF. (Check Adam
Farson's site about this.) It both improves selevtivity and it makes the PBT
to get much better.

The next improvment after that would be an 9M 250Hz filter for CW. Then I
would choose Icom FL- 101 as Inrad's filter is do not fit and has to be
wired in.

Next, I would go for the 250Hz Inrad for 9MHz IF. Then it is also possible
to use PBT to get any bandwith between 250 and 100Hz or so.

After that I would consider narrow SSB filters. Actually with the Inrad #109
in the FL-96's place you can use PBT to get the bandwith of your desire, and
in real life the IMD of the other's transmitters will limit how close you
can get, thereby you will have limited use of narrower SSB filter. But on
the other hand, there is place for more filters so why not try? I would go
for the Icom FL-223 in the 9MHz IF and an INRAD in the 455kHz IF 2100 or
1800Hz. Probably 2100 as I do think Icom FL-222 that is 1,9 or 1,8 depending
up on leafleat, cuts to much of the audio making just hard to copy.

Remember that no mater you buy a bunch of filters or not you still can use
the filters you have togher with the PBT and get any bandwith you like. Ok
matched filters in a particular bandwith will give you the best (measured)
selectivity, but it will not be the thing that decides if you will have the
QSO or not.

An option I really would recomend before it is to late is the CR-282 TCXO.

/Anders

----- Original Message -----
From: "Skip Cameron" <scameron at austin.rr.com>
To: <sm4rna at telia.com>
Sent: Monday, June 11, 2007 8:32 PM
Subject: ICOM IC-775 Roofing Filter

> Hello Anders:
> Thanks for the comments!
> I found at the http://www.qth.com/inrad/ site under Performance 
> Enhancements that they have a $US
> 175.00  "ICOM IC-775 Roofing Filter Installation Manual"
> The curve looks impressive!
> Would this be preferred as a first improvement, and then the 9mhz 400 and 
> 2100 roofing filters if I
> want more improvement later?
> Skip W5GAI
> ---------------------------
> Anders Janis SM4RNA sm4rna at telia.com
> Mon Jun 11 13:26:01 EDT 2007
>
> Roofing filters are in 64MHz IF.
>
> If you choose from 9M och 455k the 9m is earlier than 455k in the chain 
> and
> therfore to prefere.
>
> On the other hand. If you get teh 9M filters at first you will get the 
> other
> later or regret that you did not when they are not availeble any more.
>
> The DSP filter is 80Hz by the way.
>
> /Anders
>
>
> ----- Original Message -----
> From: "Skip Cameron" <scameron at austin.rr.com>
> To: <icom at mailman.qth.net>
> Sent: Monday, June 11, 2007 6:12 PM
> Subject: [ICOM] Roofing Filters Question
>
>
>>I have an IC775DSP with 455khz and 9mhz IF's.
>> I have the stock IF filters, which are 500hz for CW and 2400hz for SSB.
>> On CW I can select wither the 2.4 or the 500, and I can also engage DSP
>> which really narrows the CW,
>> down to about 50hz.
>> For contests and split Dxing, the DSP 50 hz is too narrow on CW, 500 hz
>> works pretty good, and the
>> 2.4 is too wide on SSB, with lots of other strong signals interfering.
>> I have been considering INRAD roofing filters, 400cw and 2100SSB.
>> Would I need them in both 455 and 9 IF's?
>> If I just wanted one, not both, which would be best?
>> Skip W5GAI
>>
>
>
>
> 

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