On Wed, 23 Sep 2020 15:36:58 +0530, Pimpom wrote:
Once I even rigged up a passive re-radiator with a back-to-back
pair of yagis on a hilltop for a client who had no reception at
all in his house which was located on the blind side of the hill.
It worked somewhat but was not really satisfactory.
Passive repeaters like that don't work. For example, let's take an
over simplified situation.
This is for a direct path (no repeater) between the TV station and the
receiving antenna. UHF 14 channel at 500 MHz. 10 mile path. 12 dBi
antenna gain on the receiver end.
https://www.proxim.com/en/products/knowledge-center/calculations/calculations-free-space-loss
The 10 mile path produces a 110.6 dB path loss at 500 MHz. Add the 12
dBi antenna gain and the station to receiver path loss is:
110.6 - 12 = 98.6 dB loss
Next is with a passive repeater installed at 9 miles from the TV
station and 1 mile to the receive antenna. At the 9 mile point, there
are two back to back 12dBi UHF antennas. This splits the calculation
into two parts (9 miles and 1 mile). Note that there are three 12dBi
antennas involved:
The 9 mile path has a loss of 109.7 dB. The first 12dBi antenna
reduces the 9 mile loss to:
109.7 - 12 = 97.7 dB loss
The 1 mile path has a loss of 90.6 dB. The 2nd and 3rd 12dBi antennas
reduce the 1 mile loss to:
90.6 - 12 -12 = 66.6 dB loss
The total end to end loss (including the three 12dBi antennas) is:
97.7dB + 66.6dB = 164.3 dB path loss
164dB is a *MUCH* larger path loss than the original direct path of
98.6dB even though it includes the gain from 3 antennas (+36dB).
Specifically, the direct path signal through such a passive repeater
arrangement would be:
164.3 - 98.6 = 65.7dB
or about 4 million times stronger (in terms of power gain) than the
passive repeater derangement. This is why you don't see many passive
repeaters, passive cell phone boosters, or flat panel reflectors, in
service.
What I couldn't really explain was that reception slowly but
steadily degraded in the decade from 1980 to 1990 (when cable TV
arrived). In 1980, I could often get excellent reception in my
house with literally an aluminium coat hanger plugged into the
antenna socket. By contrast, I could watch the 1990 FIFA World
Cup only with an array of four yagis *and* an antenna booster.
1990 was before repacking and DTV (about 2009), so that wouldn't
explain the signal loss. What seems odd is your "slowly but steadily
degraded". That seems like some kind of TV receiver problem,
mechanical problem (squirrel chewing coax, water in the coax, antenna
rot), that gets worse over time, rather than a sudden change. Were
the neighbors experiencing the same problem with the same station? Are
you on a shared community or building distribution system? Were you
listening directly to the unspecified TV transmitter, or were you
listening to a station owned UHF repeater?
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558