Quote:
Originally Posted by jrgagne99
It seems that the 33-2230 UVSJ is greatly attenuating my UHF signals.
It would seem that I should try a different brand of UVSJ. I would rather like to avoid two lines and an A/B switch.
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That got me curious, so I made some measurements to compare four UVSJs:
MCM 33-2230
Radio Shack 15-2586
Antennas Direct EU385CF-1S
Macom (Old)
For the first measurements, I used a Blonder Tongue HAVM-1UA Frequency Agile Modulator as a stable signal source, and a Sadelco DisplayMax 800 Signal Level Meter. The modulator puts out an analog signal; I used the video carrier for each channel. The Sadelco meter has 0.1 dB resolution.
I was having a problem getting consistent measurements. The Sadelco meter has a built-in calibration reference and at certain intervals will correct its readings. This was difficult for me to deal with when making 0.1 dB resolution measurements, so I switched to my Sadelco 719E meter that has a panel meter with wide 1 dB divisions in the center of the scale that allows me to interpolate to the nearest 0.1 dB.
The Sadelco 719E is on the left; the DisplayMax 800 on the right:
I used the red divisions and the second scale -10 to +20 dBmV.
I would read that as +2.8 dBmV.
To make a measurement, I first connected the modulator to the meter with an F-81 adapter and took a reading. I then substituted the UVSJ, UHF and common ports, for the adapter for the second reading.
There was an attenuator at the output of the modulator and at the input of the meter to try to keep the line "flat" (low SWR).
Code:
UHF Insertion Loss of Four UVSJs
CH MCM 33-2230 RS 15-2586 AD EU385CF-1S Macom (Old)
F-81 UVSJ Loss F-81 UVSJ Loss F-81 UVSJ Loss F-81 UVSJ Loss
---dBmV-- -dB- ---dBmV-- -dB- ---dBmV-- -dB- ---dBmV-- -dB-
15 7.1 5.8 1.3 7.1 6.5 0.6 7.1 6.8 0.3 7.1 7.0 0.1
28 6.1 5.4 0.7 6.1 5.5 0.6 6.2 5.8 0.4 6.2 6.1 0.1
45 5.3 4.3 1.0 5.3 5.0 0.3 5.3 4.9 0.4 5.3 5.2 0.1
The MCM 33-2230 does have a higher insertion loss that might make a difference if your marginal signals are at the "Digital Cliff."
The Macom UVSJ has very low loss because it has fewer components.
L1, C1, and L2 are the lowpass VHF filter; C2, L4, C3, and L3 are the UHF highpass filter.
This UVSJ will pass power to a preamp for the VHF antenna through L1 and L2.