Originally Posted by marcello696
got the new preamp yesterday and while Im still not getting KCOP or KFLA (not a big deal)
I am getting KCAL at 75% signal strength but I noticed that from 6pm until 10pm signal strength dropped to under 20% and unwatchable.
All the other VHF and UHF channels are rock solid, any idea what could cause KCAL to lose that much signal strength?
Could be KCAL transmitter power level changes.....or one of the other strong nearby signals is changing,
which in turn is changing the INTERFERENCE levels. Or maybe YOU or a neighbor comes home and turns
on an interference source, such as Fluorescent lights (some CFL's can be quite BAD).
Ch12 (K12PO) is a repeater for San Diego's KUSI, located north of I15/I215 split, about
1-mi East of I215 off Clinton Keith Road....my son is a bit further East....
[BTW: Analog KDUG Ch21 is about 1-mi West of I215...and Ch27 has been off the air for awhile].
KXFG-FM (92.5 MHz) is co-located with K12PO....only 6 kW, but it's very close.
KTMQ-FM (103.3 MHz) and KMYT-FM (94.5 MHz) are further away, but with higher power.
Local Ch12 can make reception of adjacent Ch11 (KTTV Fox) and Ch13 (KCOP MyN) quite difficult.
Outdoors we've used side-lobe null directed towards Ch12 to receive these stations, but in the
attic it has been very hit and (mostly) miss....even after we tweaked YA-1713 antenna position to
null out Ch12 (required a LOT of attenuation before the signal was weak enough to see changes).
Fortuitously, the YA-1713 sidelobe angle was very close to what we needed....
Second Harmonic of Local 92.5 MHz is 185 MHz, which acts as adjacent channel interference
to Ch9 on 189 MHz....and second harmonic of 94.5 MHz lies directly on Ch9. A Preamp will
readily generate these harmonic interference signals....esp. high gain Preamps.....unless
attenuated by FM Notch Filters or preferably Full Band Stop Filters, since Notch Filter
effective bandwidth is only on the order of 1 MHz or so....factory tuned to protect Ch6.
It is also a possibility that Third Order INTERMOD products are interfering with Ch9 (KCAL)
and even Ch7 (KABC)....I see five combinations of the above freqs that lie on top of Ch9.
I don't know what the Gain is in the FM Band for the A-D C5, but I have modeled the
similar Loop+ScreenReflector, which had about -2 to -4 dBi Gain in FM Band:http://imageevent.com/holl_ands/loops/looprefl
FWIW: 4nec2 model for YA-1713 calculated about -1 dBi Gain in FM Band, so it too is
receiving quite a bit of the available FM signal energy.