Mark Erbaugh wrote:
>Did you make any comparisions between then 400 Hz roofing filter and the
stock roofing filter?
Carl N4PY wrote:
>Have you been successful at actually finding a real world situation where
any of the add on roofing filters helped to copy a station?
I'll try answering these questions together with general comments on
roofing filters. First, for normal use, I would say that NO additional roofing
filters should be necessary. The main purpose of the roofing filter is to
reduce strong adjacent signals that might fall within the passband and cause
IMD products at later IF stages. Unless you have unwanted signals that are
~S9+30dB (the point at which Orion will begin to have IMD products) falling
within the stock 2400 Hz (for SSB) or 1000 Hz (for CW) roofing filters, then
optional roofing filters are unnecessary. These conditions are normally only
seen in the following cases:
1. Contests.
2. Large DX-pileups (with small splits).
3. A nearby neighbor.
4. 80 or 160 meters where USA signals can be extremely strong.
If you don't have any of these cases, save your money and don't get any
optional filters. However, all of these fit my operating habits at one
time or another.
Originally I planned to only add the Inrad 400 Hz filter, thinking that
I would never need anything tighter on SSB than the stock 2400, and that
nobody would get closer to me than +/- 225 Hz on CW (which the Inrad's
455 Hz BW would take care of). After experiencing a few pileups on 160
with very close, very strong signals, I felt I might need the 250 Hz after all,
although I hasten to add that I have NEVER heard a single IMD product
in Orion that I could identify. I started looking for a used TT219 but found
a nearly new set of 3 (217/218/219) that I got for $180. I briefly measured
the 217 to compare it to the Inrad and then sold it, keeping the 218 (1800)
and 219 (250). BTW, be careful about buying used filters...I found two that
had excessive insertion loss. One I returned to the seller and one was
replaced by Ten-Tec (thank you TT!).
Mark, to answer your question, I believe either a TT 217 or the
Inrad 400 would be a worthwhile CW addition if you do any of the things
I mentioned above. If not, save your money. BTW, shape factor beyond
20 to 30 dB below the passband is not critical since this area is below
the point where any IMD products will be created in Orion. So I would
just get the most economical filters (TT or Inrad) that you come across.
The differences in bandwidth and shape factor are insignificant.
Carl, to answer your question, the only place I've seen where I
feel optional roofing filters are a must is under certain QRN conditions on
160. There are times when I prefer setting DSP to a fairly wide bandwidth,
and locking the roofing filter to either the 500 or 250 positions. In these
cases, I'm effectively taking the DSP out of the picture and using only
the bandwidth of the roofing filters. I'll be able to say more about the
optional CW filters after the CQWW CW Contest.
I'll repeat that I was extremely impressed with Orion in the CQWW
SSB using the 1800 Hz filter. It could well be that the 2400 would have
worked just as well, but for $60 I was happy to have the 1800. In the
CQWW, I had the following score compared to the top 3 USA Multi-Multis
on 10 meters, so something must have been working right. All have much
bigger antenna systems and of course they have higher multipliers because
they use packet, dual operators per band, etc...but QSO's are a fairly good
indicator (although they probably have more USA in their total QSOs than I do).
Call QSO's/Zones/Countries
K9NS 1940/34/153
KC1XX 1894/32/145
W3LPL 1717/35/147
W4ZV 1937/35/138
73, Bill W4ZV
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