On Sunday, June 22, 2003, at 12:05 PM, John Rippey wrote:
> My OMNI VI (Opt. 3)'s 500 Hz first IF filter causes a drop of about 1
> 1/2 "S" units when inserted into the filter chain. The other four
> filters cause no problems. So either the 500 Hz filter is defective, or
> something more sinister is at work. (It is not loose.)
This sounds like a problem to me, try reseating the filter a few times,
and then try resoldering all the filter connections on the board. These
are the two simple fixes and are often the source of loss. You might
also make sure the gain equalization is correct, there is a jumper next
to the filter location where the gain should be set for the NAR CW
filter. This may also be a problem if not set correctly.
> 2. Any views as to whether the Inrad 400 Hz substitute in the first IF
> would be a better choice? (I tend to favor T-T filters because their
> center frequencies and skirts seem to be well matched to the receiver.)
I prefer the INRAD 400 Hz filters as they have lower loss and the skirts
are a bit steeper. Others prefer the NS (Ten Tec) filters for their
characteristics. I have found no difference in ringing with side by
side tests at my QTH under varying conditions (I have full sets of
filters in both flavors and several Ten Tec rigs here). I find very
little difference in skirts, but I can tell in a pinch that the INRADS
are sharper. There are other considerations you ought to think about,
depending on your own environment.
Oh, and there is one NS filter I absolutely adore, that is the model 221
filter for the 9 MHz IF, a 250 Hz filter centered lower than normal
(around 500 Hz if I recall correctly). It just matches my ears and cuts
all the noise that my ears find annoying. In bad QRM, the Ten Tec model
221 is the cats meow for my money.
Clark
WA3JPG
|