2 replies to this topic

[Reely340]

I've read about gaining 3dB or so from doing the saw filter mod.
I think I understood that the reduced bandwidth gives better reception qualities to the receiver.

IIRC people were switching to the ECS-D480A saw filter which has at 3dB a pass bandwidth
of only 17.6MHz and comes with the usual insertion loss of 19-20dB.

BUT
I was wondering whether the gain for the receiver could much bigger when using a [b]low insertion loss saw filter[/b] like the VANLONG SF480 which has a rather normal 22dB bandwidth but comes with only 2.5dB insertion loss!

Wouldn't that mean the signal is not dampened by the usual 25-18dB insertion loss but only by 2.5dB,
hence "attenuating" the signal by 15dB or more!

I'm bad at rf technology, and don't know whether subtracting the dB numbers is correct but I don't understand why only the 480MHz saw filters have such a high insertion loss, check out that VanLong SAW Filter table, third column.
Only "our frequency" of 480MHz saw filters have that 20dB insertion loss, except for the SF480 (w/o any dashes).

Any satellite rf tech willing to clarify?

I'm trying to get that SF450 2.5dB il to mod one of my 12 channel receivers to test that.
Seems this eurpean VanLong distributor is rather uhm slow at responding to mails.

[Mr.RC-Cam]

Unfortunately the SF480 is a RF filter, not a IF filter. Both are used in a receiver's design, but they are not for the same purpose. The reason the IF filters have the higher insertion attenuation is due to their needed precision.

Perhaps it would be interesting to see if the RF filter could be used in the IF location, but I don't expect it would be a drop in swap. So be sure to report back your test results.

[oscilentinc]

hey guys you know you might be able to utilize a rf filter here. the hardest part would e to find out that matched the output or impedance flow . I'd be interested to try. I found this site it's got a ton of rf filter specs. http://www.oscilent...._saw_filter.htm