AVS Forum banner

Status
Not open for further replies.
1 - 4 of 4 Posts

·
Registered
Joined
·
111 Posts
Discussion Starter · #1 ·
I just purchased and installed a Channel Master 7777 preamp and am having a

small problem. I bought the preamp because it had separate vhf and uhf

inputs. The antennas I'm using are a Channel Master 4228 (primarily for UHF

reception of digital channels) and a Radio Shack VU-120 (for FM and VHF),

but they are not cooperating.


My priorities are from highest to lowest:

UHF reception of digital channels (with a wide range of power and distance)

FM radio reception

UHF analog and VHF-hi channels

VHF-lo channels


With just the 4228 hooked up and the preamp set to separate, UHF comes in

fine. FM and VHF-hi come in (but not great). If the switch is preamp is

set to combined input, VHF-lo comes in fuzzy as well.


With just the VU-120 hooked up to the VHF input and the preamp to separate,

FM, VHF-lo and VHF-hi come in fine, but UHF has problems (mostly multipath).


With both antennas hooked up and the preamp set to separate inputs, VHF-lo

comes in fine, VHF-hi and UHF come in with problems, including enough ghosts

to cause problems with digital reception. I didn't check FM reception with

both antennas hooked up. I physically removed most of the UHF portion of

the VU-120 antenna (only the "bowtie" remained), and that helped but didn't

eliminate the UHF conflict.


Anyway, it appears that the preamp does not filter UHF signals from the VHF

input when the preamp is set to separate inputs. It also appears that the

cutoff for VHF from the UHF input is set at too low of a frequency for my

needs.


So now for the questions:

Is it possible to modify the 7777 to filter out VHF hi and lo as well as FM

from the UHF input, and filter UHF from the VHF input?


Would I be better off getting a model 0549 UHF - VHF/FM joiner/separator ( http://www.channelmaster.com/pages/cjs1.htm ),

connecting both antennas to the joiner, and then connecting the output of

the joiner to the preamp using the combined input?


Any other suggestions for getting these two antennas and preamp to work

together to accomplish my reception goals?


(a copy of this message was also sent to Channel Master)
 

·
Registered
Joined
·
780 Posts
gpb: I believe that you are on the right track, but with one suggestion. Get TWO of the CM 0549's and put them in front of the CM 7777, one for each antenna lead (UHF and VHF respectively). You will note that the lead from the UHF antenna go to the UHF input of the CM 0549 and the VHF antenna lead to the VHF input of the second CM 0549. Terminate the unused inputs with 75 ohm terminating connectors. The CM 0549 has a low insertion loss and should filter the UHF and VHF signals very well in your configuration ( based upon my experience with a similar antenna configuration)


Regards
 

·
Registered
Joined
·
887 Posts
gpb,


Do you have the FM trap switched "in" or "out"? If it's out,you may have some intermodulation distortion,caused by strong local FM stations.I've always read it's better to use a seperate antenna for FM,with no preamplification.


I think the 7777 has seperate bandpass amplification and then recombines at the output,but I'm not positive on that.


Hope you get the problem resolved.It can be frustrating.
 

·
Registered
Joined
·
111 Posts
Discussion Starter · #4 ·
Quote:
Originally posted by MAX HD
gpb,


Do you have the FM trap switched "in" or "out"? If it's out,you may have some intermodulation distortion,caused by strong local FM stations.I've always read it's better to use a seperate antenna for FM,with no preamplification.


I think the 7777 has seperate bandpass amplification and then recombines at the output,but I'm not positive on that.


Hope you get the problem resolved.It can be frustrating.
I am not using the FM trap. If I understand how the preamp is supposed to be working, the UHF and VHF signals should be amplified, and the FM should pass through unboosted. I'm willing to live with the picture interference caused by the FM as I usually watch digital TV. Only one station with FM interference isn't broadcasting digital yet, and it should be on the air within a month.
 
1 - 4 of 4 Posts
Status
Not open for further replies.
Top