DETAILED OVERLOAD CALCULATIONS FOR KEENAN'S LOCATION:
The below spread sheet shows that the CM-7777 will be overloaded if antenna is
pointed to any of the local stations. The HDTV Tuner may also be overloaded.
When pointed towards Sutro Towers with one of the sidelobe notches pointed towards
A-KRCB and KRCB-DT (9.5 miles away), the CM-7777 will be overloaded by KRCB-DT.
Also overloaded by A-KTLN and KTLN-DT, that are directly on the line to Sutro Towers.
The HDTV Tuner may also be overloaded, but can be avoided by inserting attenuation
on the Tuner input (e.g. RF Splitters or R-S Variable RF Attenuator).
Note that the sidelobe notch is much deeper for A-KRCB on CH51 (I assumed 20 dB)
than it is for KRCB-DT on CH23 (I assumed 10 dB).
Since I have not seen antenna pattern measurements or NEC simulations for the
XG-91 type antenna, I assumed that it was similiar to the high-gain CM-4228 antenna,
using NEC Sim results found in www.hdtvprimer.com/ANTENNAS/comparing.html
When the specs for the new Winegard HDP-269 were entered, all of the Preamp
overload problems were not only cured, but the input signal was 15-20 dB below
the specified overload point, which maximizes the Spurious Free Dynamic Range
so that intermods are pushed down towards the noise floor. This facilitates
reception of the weakest signals from remote locations.
With only 12 dB of gain in the HDT-269, the input level to the HDTV Tuner was still
uncomfortably close to what I have seen specified for maximum input levels.
This can be avoided by inserting a small amount of attenuation prior to the Tuner,
e.g. RF Splitter(s) and/or a R-S Variable RF Attenuator.
I didn't take the time to tailor RADIO MOBILE for the S.F. area, so some of the path loss
numbers are "best guesses" based on performing similiar runs in LA and San Diego area.
So there is still a useful exercise left for the interested student....
Let me know if you find any errors in the spread sheets....no really...
1. Found a small error in the Off-Beam Rcv Ant Gain when pointed towards
Sutro Tower and using W-G HDP-269 Preamp.
Now it's the same as for CM-7777, which was correct to begin with.
2. deconvolver found an error: A-KRCB should be CH22 (vice my KUSI on CH51).
This also changes the Antenna Gain and Off-Beam notch depth, resulting in
a stronger overload contribution. A-KRCB is the second strongest overload source
and KRCB-DT is still the strongest overload signal when pointed toward Sutro Towers.
3. The KTLN-DT and A-KTLN broadcast antenna gain corrections (voltage not power) were incorrect.
This results in reduction in the overload contribution from these stations by several dB,
but they remain lurking just below the CM-7777 spec overload level.
4. In double checking, I found that KDTV-DT should be A-KDTV, which deletes
the 8 dB Average to Peak Power conversion.
This wasn't the principal problem before and is even less so now.
I also added calculations for the W-G AP-4700 (or equal) Preamp:
RevC spread sheet has been replaced by RevD:
SF DTV_Overload_Calc_RevD.zip 12.677734375k . file