What type/brand of amplifier are you using? I have found that some of the noisier high gain amplifiers actually do more harm than good (to a digital signal). Have you tried removing the amp? Also, if your amp has an FM trap, is it on or off?
You shouldn't be needing any amplifier in Manassas except for maybe channel 50 or 22. Channel 30, broadcasting from just south of Manassas is most certainly overloading your amplifier. A good rooftop antenna with a low gain pre-amp (12 db), or a quality distribution amp should provide excellent reception for you. Channel 7 & 9 have always had a very robust, easy to recieve signal in Manassas.
Thanks everyone for suggestions (my first post on page 357,http://www.avsforum.com/avs-vb/showt...8#post17220828
). Here is a bit more about my setup in Manassas: some kind of rooftop antenna is in the attic - don't know brand and don't know whether it is VHF/UHF or just UHF. Then RadioShack amplifier (I think it is 36 db, but maybe 24) and then 2 2-way splitters. My first digital to analog tuner is after the first splitter relatively close to amplifier. My HDTV sits after both splitters and relatively long cable run. Like I said, before the DTV switch I had a bit noisy, but watchable analog channels and after buying HDTV very watchable same digital channels.
Among analog VHF WUSA (9) was the best and 7 WJLA was close second. 5 was worse and ch. 4 was difficult to watch. So I deduct that my antenna has VHF capability.
Ch 14, 20, 26 were very good. When putting amplifier and orienting antenna I've spent quite a time to figure the best reception and amplifier is on max gain, reducing the gain slightly degraded weak channels. Before putting in amplifier I've tried just antenna - almost everything was very weak and noisy.
So, after the switch, 7 and 9 disappeared, being the most strong analog channles. Heck, I even found official very detailed map, which shows that in my location there should be no change whatsoever in reception after the switch. The only reason I could think of is that with the switch power of the transmitters was reduced thinking that digital signal is more protected against noise.
After increasing power on 7 I see 40% of strength on my digital to analog tuner and almost no dropouts. Whereas 9 shows also 40%, but then dropouts are frequent and during them slider jumps between 0 and 20%. I tried to experiment by Steve's suggestion with FM trap on amp. It has 2 positions "in" and "Off" and always been in "in" position. When I switch to "off" channel 7 goes from 40% to 0% right away.
All other channels are at 100% except a couple very close at 90-95%.
HDTV at the end of the line shows ch.7 at 20% and after long stable reception 10 - 120 minutes bad dropouts suddenly appear for 1 - 30 minutes. I considered that something interferes with a signal - my first thought was - refrigerator. But after observing for several days - I cannot pinpoint the problem in the house, maybe something outside. Air conditioning is completely off these days.
So if anything - I consider putting addtional 10 db amplifier for the HDTV line only, providing that increase in power on 7 is permanent.