Improve reception with new antenna?

no_pay_tv

DTVUSA Jr. Member
#1
I'd like to improve the signal strength at our TVs to avoid periodic failures. I am currently receiving all desired channels using an old Radio Shack VHF/UHF antenna, but the signal strength is just barely high enough at the TV to receive some channels, so we occassionally lose them. The antenna is approximately 15 years old and is still in good condition. I'm not sure of the Radio Shack model number, but I think it may be a VU-160. It is approximately 140" long and 64" wide and has 16 VHF and and 25 UHF elements. I have it eave mounted with the antenna about 5' above roof line (~ 20' from ground). I was previously using an old Radio Shack preamp with it, but recently replace it with a Channel Master 7777 since I read that the Radio Shack preamps were rather noisy. Unfortunately upgrading to the CM7777 preamp didn't improve the signal strength measurably, which I don't understand. Apparently the Radio Shack preamp I was using isn't that bad after all.

I attached results from TVFool.com. We are satisfied to receive the following channels listed in order of decreasing signal strength: 39 (39.1), 46 (69.1), 6 (6.1), 26 (3.1), 17 (17.1), 34 (10.1), 12 (12.1), 42 (29.1), 31 (61.1), 32 (57.1). Currently 12, 42, 31, and 32 are the ones that drop out the most, which I'd expect based on the signal levels. All of the low level signals we are attempting to receive are in the same direction, which eliminate the need for a rotor. I currently do have a rotor and found the exact orientation required to have any chance at receiving these channels - any tweaks from this direction and I lose the weakest signals.

I'm hoping that replacing the antenna will solve my problems and hope to get some advice. Note that there is one channel (6) in the low VHF band, one channel (12) in the high VHF band, and we also use the antenna to receive FM. This all leads me to believe that I should go with one of the following antennas:
Channel Master CM3671
Winegard HD8200U
Winegard HD7084P

I was hoping I could get by with a smaller antenna designed for channels 7-69 like the Winegard HD7697P or HD7698P, but I'm not sure if I would end up losing channel 6 and FM.

It's nice to know that there are still some other people out there who still use antennas and hopefully know more than I do.
 

Attachments

EscapeVelocity

Moderator, , Webmaster of EV's Antenna Blog
#2
Is this the antenna you have? Also is it just me, or is that TVFool image really small and degrades badly when zoomed, making it unreadable?

 

Piggie

Super Moderator
#4
I was hoping I could get by with a smaller antenna designed for channels 7-69 like the Winegard HD7697P or HD7698P, but I'm not sure if I would end up losing channel 6 and FM.

It's nice to know that there are still some other people out there who still use antennas and hopefully know more than I do.
If you can receive a channel 6 now, and want FM, then you can't use a Winegard 769xP series antenna. You are correct about that.

I currently am not recommending specific antennas, being a moderator I put myself in a compromised situation, though I do have strong strong preferences for different antennas.
 
#7
Currently 12, 42, 31, and 32 are the ones that drop out the most, which I'd expect based on the signal levels.
Based on your tvfool report I'd guess that your amplifier has too much gain. Channel 12 can receive harmonic interference from WCTO FM, Channels 31 & 32 are prone to intermodulation distortion from channels 39 & 46. Both of those issues occur when an amplifier has too much gain.

The HDP-269 shouldn't overload, but the gain is marginal.

The AP 8700 is a better choice and has a tunable FM trap.
 

IDRick

DTVUSA Member
#8
Hi Tower Guy!

Can you provide more detail on this statement: "Channels 31 & 32 are prone to intermodulation distortion from channels 39 & 46."? How did you arrive at this conclusion? I'm not challenging, just wanting to learn. :)

Best,

Rick
 

no_pay_tv

DTVUSA Jr. Member
#9
Can you also plot an exact address FM Fool?
I did plot to my exact address. tvfool just doesn't display it.

Based on your tvfool report I'd guess that your amplifier has too much gain.
The AP 8700 is a better choice
Please explain. I checked the maximum input levels on the CM 7777 before purchasing to verify that overload would not be a problem and the noise level is slightly better than the AP 8700. Without the preamp I lose the channels I mention as being problematic since the signal strength is weak.
 

EscapeVelocity

Moderator, , Webmaster of EV's Antenna Blog
#10
Hello nopaytv,

I was hoping maybe you could provide a link to an exact address FMFool, that is FM not TV. It wont show your exact address either, but it will show local FM broadcasters, directions and power levels, and so on and so forth.
 

no_pay_tv

DTVUSA Jr. Member
#12
I was hoping maybe you could provide a link to an exact address FMFool, that is FM not TV. It wont show your exact address either, but it will show local FM broadcasters, directions and power levels, and so on and so forth.
Unfortunately fmfool doesn't allow me to link to the URL with the results, so I saved the image (png format) and uploaded it. It looks fine on my PC, but I see that when I upload the image it shrinks to a fraction of the original size. I converted the png format to jpg on my PC and uploaded again and now the uploaded image looks better. It may be helpful to others to note that saving the tvfool and fmfool results as png don't scale well when uploaded.
 

Attachments

#13
Hi Tower Guy!

Can you provide more detail on this statement: "Channels 31 & 32 are prone to intermodulation distortion from channels 39 & 46."? How did you arrive at this conclusion? I'm not challenging, just wanting to learn. :)

Best,

Rick
Third order intermodulation occurs when two frequencies create phantom signals signals above and below.

In this case (F1-F2)+F1 falls on channels 53 and 54. F2-(F1-F2) falls on channels 31 and 32.
 
#14
I did plot to my exact address. tvfool just doesn't display it.



Please explain. I checked the maximum input levels on the CM 7777 before purchasing to verify that overload would not be a problem and the noise level is slightly better than the AP 8700. Without the preamp I lose the channels I mention as being problematic since the signal strength is weak.
An amplifier creates a small amount of third order intermodulation even when it is not overloaded.

I'm not sure that IM is your problem, but your symptoms match a non-linear amplifier.
 

no_pay_tv

DTVUSA Jr. Member
#15
I did plot to my exact address. tvfool just doesn't display it.



Please explain. I checked the maximum input levels on the CM 7777 before purchasing to verify that overload would not be a problem and the noise level is slightly better than the AP 8700. Without the preamp I lose the channels I mention as being problematic since the signal strength is weak.
An amplifier creates a small amount of third order intermodulation even when it is not overloaded.

I'm not sure that IM is your problem, but your symptoms match a non-linear amplifier.
I should also note that the CM 7777 came with the FM trap enabled and I installed it that way. I still receive the FM stations I am interested in although they are supposedly being trapped. Don't know how to explain that or if that helps determine how to improve what displays as weak signal strength at our TV for specific channels.
 

no_pay_tv

DTVUSA Jr. Member
#16
I left some details out of my original post and I'm not sure if this is important.
I'm using an old radio shack balun at the antenna, 2 feet of coax between the balun and amp and approximately 75 feet of coax between the amp and power supply. I then have a two way splitter and one split travels 15 feet before going through another two way splitter to connect to both an HDTV and a converter box for an old VCR. The other half of the original split travels 50 feet before going through another two way splitter to connect to both a converter box and my FM receiver. I hope this information is also useful.
 

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