CM7777 with separate VHF/UHF inputs - Canadian TV, Computing and Home Theatre Forums

 
LinkBack Thread Tools Search this Thread Display Modes

post #1 of 9 (permalink) Old 2017-07-29, 11:29 AM Thread Starter
Rookie
 
Join Date: Jul 2008
Location: 1000 Islands, ON
Posts: 21
CM7777 with separate VHF/UHF inputs

I have an older dual input CM7777 that was configured for separate inputs with a 91XG/CM3617 setup. In an effort to avoid the use of a rotor, I decided to remove the tired 3617 and combine the 91XG pointing northeast with a CM4221 pointing south.
Since VHF in my area is only CH 7 & 11, I expected that the CM4221 would perform well for the local VHF work and do a good job for Watertown NY UHF channels.

I did not change the switch from separate inputs and while the VHF is notably improved from the interim the 91XG only , I don't seem to be getting any UHF from the 4221.

Do the separate inputs feed to separate VHF /UHF preamp sections in the dual input 7777?

If so that would possibly explain why I am seeing only VHF improvement 4221.

Last edited by abbie; 2017-07-29 at 11:32 AM. Reason: removed duplicate words
abbie is offline  
Sponsored Links
Advertisement
 
post #2 of 9 (permalink) Old 2017-07-29, 12:34 PM
 
Join Date: Dec 2008
Location: Mississauga
Posts: 814
If you feed the 4221 into the VHF port on the amp then all you will receive is VHF and if you feed the 4221 into the UHF port on the amp then all you will receive is UHF. The reason for the two ports is to prevent 2 antennas, one VHF and the other UHF from interfering with each other when joined together.

FTA, Openbox S9, 33” dish, Avenger PLL LNBF. Stab 90HH.
OTA, CM4221HD, 3410 amp, 4 way split, HW-150 PVR
Jorgek is offline  
post #3 of 9 (permalink) Old 2017-07-29, 03:15 PM
Veteran
 
Join Date: Nov 2008
Location: San Diego, CA
Posts: 3,191
Original CM7777 has SEPARATE VHF and UHF Amplifier Sections, as can be seen towards bottom of fol. Webpage:
OTA Reception Files

Note that while the NEW CM7777 probably has Separate VHF and UHF Section (I don't know), it does NOT have Separate VHF and UHF INPUTS.

Antenna Simulations, Overload Calculations, etc: http://imageevent.com/holl_ands
holl_ands is online now  
 
post #4 of 9 (permalink) Old 2017-07-29, 03:52 PM
DHC Supporter
 
Join Date: May 2010
Location: S.E. VA
Posts: 811
Here is a report centered on Lansdowne
TV Fool

If I add the postal code K0E 1L0, the report is centered on the Canada Border Svc just west of Lansdowne
TV Fool

That CM3617 is a BIG antenna!


If you can not measure it, you can not improve it.
Lord Kelvin, 1883

Last edited by rabbit73; 2017-07-29 at 04:25 PM.
rabbit73 is offline  
post #5 of 9 (permalink) Old 2017-07-29, 09:06 PM
Veteran
 
Join Date: Jun 2011
Location: 43° N, 81.2° W
Posts: 6,614
The VHF input on the CM7777 will filter out any UHF channels it receives That explains why there are no Watertown UHF channels from the 4221. A combined UHF+VHF amplifier will be required for that antenna.
ExDilbert is online now  
post #6 of 9 (permalink) Old 2017-07-29, 09:33 PM Thread Starter
Rookie
 
Join Date: Jul 2008
Location: 1000 Islands, ON
Posts: 21
Thanks for the help here especially the data and photos of the boards in the original 7777 . This would explain the bleak performance from the 4221HD

I have several options to consider then to get the uhf from the 4221

1. Move input switch to combined vhf/uhf input and connect both antennas with a combiner and feed into the combined input of the original 7777

2. Use a new version 7777 i have access to , use combiner ahead of the single input.

Any recommendations on which would be a better choice?


& yes that 3617 was quite an antenna especially for VHF low work.
abbie is offline  
post #7 of 9 (permalink) Old 2017-07-29, 09:46 PM
Veteran
 
Join Date: Jan 2009
Posts: 4,359
I would argue one is always better off using separate antennas for VHF and UHF.
Since rarely will the optimum aim for VHF be identical to the optimum aim for UHF
at a given location. So, to get the most from each band, we should be using separate antennas
whenever possible.

DB4E/VHF Yagi rotor FM Bandstop ap-8700 preamp 4way split LG lcd.
majortom is online now  
post #8 of 9 (permalink) Old 2017-07-29, 09:51 PM
Veteran
 
Join Date: Jun 2011
Location: 43° N, 81.2° W
Posts: 6,614
Apart from possibly different specs for the two CM7777s, there is basically no difference between the two options. I don't normally recommend combining two UHF or two VHF antennas due to the possible introduction of interference or multipath. Every situation is different so it's worth a try. Just be aware that it may cause reception problems on some channels.
ExDilbert is online now  
post #9 of 9 (permalink) Old 2017-08-02, 08:02 AM
 
Join Date: Nov 2008
Location: Kanata
Posts: 534
abbie,

Can you check your private messages (in your User CP), please?
DXer is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Canadian TV, Computing and Home Theatre Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools Search this Thread
Show Printable Version Show Printable Version
Email this Page Email this Page
Search this Thread:

Advanced Search
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome