[mblrds]

In shopping around for a Pre-amp there are models that have switchable FM traps; In or Out.

I understand what the FM trap is suppose to do.


Then there are models that also have switchable VHF; Separate or Combined. Usually found on models that have separate UHF/VHF inputs.


What is this switch suppose to do?

 

[bfoster]

The amps have two inputs but you can switch to combined and use a single antenna with a single feed to one of the two inputs.

 

[mblrds]

So,


if you're using two separate antennas; a UHF and a VHF, and have them hooked up to the amp at their respective hookups you would want to use the "Separate" selection?


If you were using only a UHF/VHF/FM combo antenna hooked up to the VHF input you'd want to have "Combined" selected?


If the switch was set at "Separate" you would only recieve VHF signals from the UHF/VHF/FM combo antenna?

 

[bfoster]

Probably. Depends on how good the filtering is.

 

[Rick0725]



Quote:
if you're using two separate antennas; a UHF and a VHF, and have them hooked up to the amp at their respective hookups you would want to use the "Separate" selection?

correct

Quote:
If you were using only a UHF/VHF/FM combo antenna hooked up to the VHF input you'd want to have "Combined" selected?

A combo antenna is connected to the COMBINED INPUT with the switch set to COMMON to amplify the combined vhf and uhf signal off the antenna.

Quote:
If the switch was set at "Separate" you would only recieve VHF signals from the UHF/VHF/FM combo antenna?

If you are using the cm3018 which you have for VHF and the 91xg for uhf

The cm3018 connects to the VHF INPUT and the 91XG to the uhf input with the switch set to SEPARATE.


The fm switch inside is set to ON to attenuate (trap) the fm band to lessen the chances of overload in your setup. If you want to use the cm3018 for FM, it is best not to amplify vhf where the fm band lies (between ch 6 and 7) otherwise you would set the switch to OUT.


If you choose to amplify only the 91xg for UHF and not amplify vhf off the cm3018, set the switch to SEPARATE, connect the 91XG to the UHF/combined input and connect nothing to the vhf input. Or you can connect the 91XG to the uhf/combined input and the switch to common (it would still work).


With the internal switch set to separate, the inputs are run through a vhf/uhf internal diplexer (similar to what the cm0549 does below). With the switch set to "combined", only the uhf/combined input is active.


If you decide not to amplify vhf, you would run a separate line (for vhf) into the home from the cm 3018 and combine the amplified uhf signal from the 91 xg off the "to tv" output of the preamp power supply (amplified uhf) and the direct line off the cm3018 with a cm0549 vhf / uhf combiner. The combined unamplified vhf and and amplified uhf signal out of the cm0549 vhf/uhf combiner is output to your tv's.


for fm, use a winegard ca 8800 tv/fm splitter to extract off the fm signal from the tv signal to your fm receiver.


good luck. it works great. just decide which approach to take and go from there.


when you assemble the 91xg, make sure the arrow on the elements are facing the FRONT of the antenna.


front -----------> back