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Discussion Starter · #1 ·
I am thinking of buying the more subtle Antenna Direct DB2 antenna for rooftop installation. But I am concerned about local channels moving back to Ch 7 and Ch 12 after cut over as they are in the VHF range.


I think DB2 is a very popular antenna. If you have one installed, could you tell me if you can get the analog Ch 7 to 12 okay?
 

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Quote:
Originally Posted by pixelation /forum/post/15522117


I am thinking of buying the more subtle Antenna Direct DB2 antenna for rooftop installation. But I am concerned about local channels moving back to Ch 7 and Ch 12 after cut over as they are in the VHF range.


I think DB2 is a very popular antenna. If you have one installed, could you tell me if you can get the analog Ch 7 to 12 okay?

The DB2 is a UHF antenna. If you are close enough to powerful enough stations, it may work in the VHF-hi band, or not. You may need to a simple vhf-hi antenna.
 

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I have the step up from this with the DB4 and I can say that Hi-VHF is going to be hit or miss. The closer to UHF the channel is you get the better it comes in. Distance from transmitters will also play a huge role on reception.
 

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This question can't really be answered without knowing where you are in relation to the transmitters - post back with your zip code.

In general, small antennas will be poor performers on VHF, it's the physics of antenna design.
 

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Discussion Starter · #5 ·
I have attached the tvfool post cut off chart. As you can see, I have 2 major channels (KGO and KNTV) that is using VHF-Hi. They are 32-36 miles away. Thanks in advance for the help.
 

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My hunch: You'll get those two stations in some of the time, but reception won't be very reliable. A DB4 would be a better bet, but probably not fool-proof, as POWERFUL pointed out. The only way to be sure would be to put up either one and try it.


If a single antenna doesn't work to your satisfaction, there's a fairly straightforward fix: Add an inexpensive VHF-high antenna such as the AntennaCraft Y5-7-13 Yagi (60" boom, 36" max. width), and combine its output with that of the DB2/DB4 into one coax downlead using a UVSJ combiner. The VHF antenna goes three feet or more below the UHF antenna on the mast.


A rooftop antenna is a sign of someone who knows that OTA HDTV picture quality beats cable and satellite HD hands down!
 

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I hate to bring old topics back to life, but I finally got around to modifying my DB2 antenna for VHF and thought you might be interested.

(Copy and paste from my blog post)


So back when the whole TV transition was just starting and I didn’t have a clue what I was doing, I bought an antenna that I thought would cover my needs. Its an Antenna Direct DB2 antenna. Its a nice Multi-directional UHF antenna and at the time it worked great because there wasn’t any VHF stations. However after the final transition, two of the major stations switched back to VHF to the channels 7 and 9. So when the world cup started on TV, I decided I needed ABC which was on channel 9. So I researched what I needed to do, and obviously I needed a VHF antenna, but I didn’t want to get rid of my current DB2 antenna. In basic I needed a simple half dipole antenna to add to my UHF antenna at the center.


Since I wanted channel 7 and 9, I found out which freq the channels broadcast in.

VHF HIGH 07 174-180 Mhz

VHF HIGH 09 186-192 Mhz


Found the calculations to get length of wire for frequency from this website here.


Formula: Length of wire = 468/frequency

Example: Length of wire = 468/180.000 Mhz (upper range of channel 7)

Length of wire = 2.6ft feet or approx 30″


I think the exact length was about 30.5″


The material I used for the antenna was some aluminum wire rod I picked up at Menards. I forgot to get the exact size but it was slightly larger then the original wire. I flattened the ends with a hammer and drilled a hole so I could mount it to the balum.


Here is the finished product. Maybe after the two antenna products I have done, maybe I should take an Electromagnetic fields Class from school… I dont want to do all that work though lol.


I would like to mention it picks up channel 7 and channel 9 now!!! So I would say this has been successful.




Link - http://akschaefer.com/wordpress/2010...o-include-vhf/


photos

http://akschaefer.com/wordpress/wp-c...6/P1010354.jpg (full resolution 4Mb)



http://akschaefer.com/wordpress/wp-c...6/P1010357.jpg (full resolution 4Mb)



 

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A similar photo popped up last summer that I forwarded to our design engineer.


He shrugged and said that, since there's no free lunch, performance somewhere else in the design pass-band will be adversely affected, primarily as unintended VSWR spikes that might affect only certain frequencies. But, if the negative effect elsewhere doesn't cause problems and it allows for improved high-VHF reception, it will probably work.
 

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Quote:
Originally Posted by tonyscha /forum/post/18810116


I hate to bring old topics back to life, but I finally got around to modifying my DB2 antenna for VHF and thought you might be interested.

What is the best way to modify the DB2 for ch 7?


1) increase the width of the screen to the 30 inches?


2) replace the screen with two 30 inch rods (centered at the intersection of the two bowties and 4 inches behind where the screen is located).


In both cases the tiny VHF lobes in the back would catch this specifically tuned ch 7 rod. Would either of these methods do better than connecting directly to balun as in Tonycha's modification?




Thank you
 

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Quote:
Originally Posted by ADTech /forum/post/18810886


A similar photo popped up last summer that I forwarded to our design engineer.


He shrugged and said that, since there's no free lunch, performance somewhere else in the design pass-band will be adversely affected, primarily as unintended VSWR spikes that might affect only certain frequencies. But, if the negative effect elsewhere doesn't cause problems and it allows for improved high-VHF reception, it will probably work.

actually I think that is where I got the idea, it was a wire hanging off each end with zip ties?


Anywho..


I added some photo links in my original post .
 
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