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Discussion Starter #21
I made this quick video a while back. Featuring the double biquad and the simple $20 amp from Canadian Tire. I'm able to easily pick up these digital channels. I don't need to adjust the antenna it's pointed somewhere between Toronto and Buffalo.


Your result may vary. I'm on the 15th floor in Kitchener. I just figure this simple antenna + amp is a good starting point to get HDTV over the air for free.

Better antennas and amps will yield better results. But with the height advantage an apartment can have you just might not need more than this.
 

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If I understand the model correctly, the sides of this antenna would be 10.5 inches (26.6 cm) as opposed to 17cm (the size of the biquad I built).

With the antenna 10.5 inches on the side and a gap, this would be similiar to the chireix antennas, yes?

http://imageevent.com/holl_ands/chireix/chireix
Yes. It looks like great minds think alike :) The gain and SWR pattern for the chireix without reflector is exactly what I got while modelling it.
 

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Discussion Starter #26
Road Tested the biquad

I was out today in the country side and tested the biquad out in the open air. Holding the antenna about 8-9ft in the air-



Here is my location (the pin marks my exact spot in southern ontario)



The tvfool report for this location

http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id=9fbe0e8f6eae91

I was only checking for digital channels using my portable LCD TV and was able to receive these channels-

4-1 WIVB, 5-1 CBLT, 7-1 WKBW, 11-1 CHCH, 15-1 CKXT, 17-1 WNED, 23-1 WNLO, 26-1 WNYB, 54-1 WQZN, 66-1 WFXP

The weakest signal was WFXP. There are some other stations in the same direction and distance that I didn't receive.

All in all, the antenna performed quite well just holding in the air. I'm sure mounted at roof top height on a proper mast it would do better. All that is needed is to make this simple antenna weatherized for the outdoors.
 

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Thats impressive.It seems that you are receiving channels quite some distance away.
Does the antenna have to have line of site to the transmitters? Have you tried it in the attic to see how it would perform there? Any ideas on how to weatherproof it to be installed outdoors should attic mounting not work?
 

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Discussion Starter #28
To answer some of your questions:

No antenna has to be line of site to work. Even rabbit ears will work. What is important is the signal strength and the gain of the antenna. Line of site stations usually have the strongest signal while 1Edge and 2Edge stations will have weaker signals.

If you look at the tvfool report there is a column labeled NM (db).

Take this number and add the gain of the antenna (this particular antenna has about 7db of gain). Then subtract all of your losses. Losses include cable length to you tv, any splitters, and if you are putting the antenna in an attic you'll lose quite a bit of db - worst case of 25db.

If the number is greater than 0 then there is a good chance you'll receive the station.

For example, in this test I picked up WQLN which has a NM of -1.3. Add the gain of the antenna and you end up with 5.7. Since the cable I'm using is really short and I'm out in the open my loss is practically zero. Since the number is greater 0 after adding the gain and subtracting the losses I should receive this station - and I did!

tvfool is approximate so if there is a local building or hill in the way it might not know about it and the NM would actually be lower than it states. This is where you should do a bit of investigative work and use Google maps to check out any obstructions near by.

----------------

I'm in the process of building an outdoor version of this antenna and will post build details. Since this antenna is so small and discreet you can easily put it outside, on the roof, or a chimney mount.

If you must put it in the attic then I would recommend building an antenna with a lot more gain like the gray hoverman so you can overcome the losses that putting an antenna in the attic would have. the gray hoverman is bigger than this antenna but should easily fit in an attic.
 

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It wouldn't necessarily have to go in the attic, I was just thinking that it might stand up better from elements. Another question. How do you calculate the loss from cable, splitters etc. to subtract from the gain of antenna?
 

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Discussion Starter #32
A two way splitter has a loss of 3.5db. Usually the splitters will have the loss marked right on output connectors.

The loss for your cable will depend on the quality of the cable. Usually, you can google the markings or manufacture on the cable and find out exactly how much loss per 100ft the cable will have. A good guess is 6db per 100ft.

If you want to eliminate the loss of the cables, splitters then you can use a preamp. For a good quality preamp subtract about 2db and you can forgot about everything after the preamp. However a preamp is not a be all end all solution. With a mix of strong local signals and distant signals you could end up with worse reception - as noted by posters in the preamp threads.

Again, all of this is approximate because I find that factors such as terrain, buildings, possible reflections off buildings causing multipath, weather etc. cause variances in trying to mathematically calculate the maximum stations you can receive.

This simple biquad is easy to make and inexpensive - less than 10 dollars. And probably will give you a pretty good idea of how good reception is in your location, whether you can use an antenna in the attic or need to get it up on the roof. Combined with tvfool and google maps you should be able to put together a plan for maximum reception.

Height of the antenna is always your friend, that's why this simple biquad works very well in my 15th floor apartment with a clear horizon towards the tv stations.
 

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Additional notes,

A two way splitter has a loss of 3.5db. Usually the splitters will have the loss marked right on output connectors.
The good ones have a loss of 3.5 db and are usually marked. If its un-marked chinese stuff, assume more like 4.5 - 5 db loss.

The loss for your cable will depend on the quality of the cable. Usually, you can google the markings or manufacture on the cable and find out exactly how much loss per 100ft the cable will have. A good guess is 6db per 100ft.
Channel Master specs 5.6 db per 100 ft at channel 51 on their RG6. About 1 db every 18 ft. The lower the channel, the lower the loss.
 

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Discussion Starter #34
Revisiting the tvfool.com tools

tvfool.com will give you a radar map showing direction and signal strength of the available channels in your area. This is the tvfool radar map showing channels from my location.



tvfool also provides an interactive map that is quite handy. For some reason using Safari on a Mac doesn't give you all the features, so you'll have to use another browser on the Mac. By clicking the 'Show lines pointing to each transmitter' you can get an accurate map showing the exact direction in relation to your apartment building.



This is quite handy as you can see from my map the only digital channels that I'm facing are:

5.1, 9.1, 11.1, 15.1, 17.1, 23.1, 25.1, 29.1, 36.1, 41.1, 44.1, 57.1, 64.1, 66.1

Channel 19.1 is on the opposite side of the building. And channels 4.1, 7.1 and 26.1 the side of the building blocks the signals. It's impossible to receive these signals through the concrete walls because they are not strong enough.

Looking at the available channel list the weakest channel would be 29.1 with a NM of -10.9db. A computer model shows this biquad has about 7 dbi of gain, so getting this channel is probably not possible.



The beam pattern is wide so pointing the antenna some where in between the 5.1 channel groupings and 11.1 groupings should pick up all the available channels without the need to adjust the antenna direction.

nec card deck for the biquad-

Code:
CM uhf biquad 2010-06-25 17:23
CE ----------
GW  1   13  0.000000  -0.01000  8.000000  0.000000  0.010000  8.000000  0.001950
GW  2   13  0.000000  -0.01000  8.000000  0.000000  -0.12374  8.123744  0.001588
GW  3   13  0.000000  -0.12374  8.123744  0.000000  0.000000  8.247487  0.001588
GW  4   13  0.000000  0.000000  8.247487  0.000000  0.123744  8.123744  0.001588
GW  5   13  0.000000  0.123744  8.123744  0.000000  0.010000  8.000000  0.001588
GW  6   13  0.000000  0.010000  8.000000  0.000000  0.123744  7.876256  0.001588
GW  7   13  0.000000  0.123744  7.876256  0.000000  0.000000  7.752513  0.001588
GW  8   13  0.000000  0.000000  7.752513  0.000000  -0.12374  7.876256  0.001588
GW  9   13  0.000000  -0.12374  7.876256  0.000000  -0.01000  8.000000  0.001588
GE  0
FR  0    1    0    0  470.0000  0.000000
EX  0    1    7    1  1.000000  0.000000                                        
XQ
RP  0    1  360 1000  90.00000     0.000     0.000     1.000 5.000E+03
RP  0  360    1 1000   -90.000     0.000     1.000     0.000 5.000E+03
RP  0   91  120 1001     0.000     0.000     2.000     3.000 5.000E+03
XQ
EN
 

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Discussion Starter #35
Mounting the antenna outside your window

Using a piece of wood, some 3/4" PVC tubing and fittings, and a PVC conduit box I was able to mount the antenna outside my window. The window screen was removed and the wood inserted in the window frame - just like the window itself is inserted.





The mounting bracket

The antenna can be described in two major components - the mounting bracket and the antenna itself. The mounting bracket is made up of piece of wood painted with exterior paint for weather proofing. A hole was drilled big enough to insert a tee into the hole.



The exterior portion has some tubing, a 90 degree elbow and about 18" of 3/4" tubing that is inserted into the tee. The coax cable is snaked through the tube and makes it's way indoors through the tee. The inside portion of the bracket has about 6" of tubing, a bracket to secure it to the wood and another elbow epoxied to the wood.
 

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Discussion Starter #36
Constructing the antenna

The antenna portion is composed of the same 17cm bi-quad built earlier. It is mounted on a 3/4" PVC conduit box. A short piece of tubing and an end cap seals the unused opening at the back of the PVC conduit box.



The hardware to bolt the bi-quad to the PVC conduit box is shown here. Use a finishing washer to bolt the bi-quad to the outside of the cover. A flat washer and bolt is used on the inside of the cover. The balun is attached between the two nuts.



Mark the holes for drilling by placing the flat washers on the inside of the cover and mark the centers. The bolts will be 2cm apart.

It is easier to snake the coax cable without a connector through the mounting bracket and into the PVC conduit box. Attach a F connector to the end of the cable after the cable has been snaked through.



Attach the balun and screw on the PVC conduit cover and you're done!
 

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Discussion Starter #37
Adding a reflector to the biquad

I also built a version of the biquad with a reflector. Using 3/8" aluminum tubing placed 14cm behind the biquad antenna. The reflectors are 40cm long and space 6cm apart.





The computer model for this biquad adds a couple of db to the gain of the antenna.



nec card deck for this bi-quad with reflector

Code:
CM uhf biquad 2010-06-25 18:11
CE ----------
GW  1   13  0.000000  -0.01000  8.000000  0.000000  0.010000  8.000000  0.001900
GW  2   13  0.000000  -0.01000  8.000000  0.000000  -0.12374  8.123744  0.001588
GW  3   13  0.000000  -0.12374  8.123744  0.000000  0.000000  8.247487  0.001588
GW  4   13  0.000000  0.000000  8.247487  0.000000  0.123744  8.123744  0.001588
GW  5   13  0.000000  0.123744  8.123744  0.000000  0.010000  8.000000  0.001588
GW  6   13  0.000000  0.010000  8.000000  0.000000  0.123744  7.876256  0.001588
GW  7   13  0.000000  0.123744  7.876256  0.000000  0.000000  7.752513  0.001588
GW  8   13  0.000000  0.000000  7.752513  0.000000  -0.12374  7.876256  0.001588
GW  9   13  0.000000  -0.12374  7.876256  0.000000  -0.01000  8.000000  0.001588
GW 10   13  -0.14000  -0.20000  8.240000  -0.14000  0.200000  8.240000  0.004763
GW 11   13  -0.14000  -0.20000  8.180000  -0.14000  0.200000  8.180000  0.004763
GW 12   13  -0.14000  -0.20000  8.120000  -0.14000  0.200000  8.120000  0.004763
GW 13   13  -0.14000  -0.20000  8.060000  -0.14000  0.200000  8.060000  0.004763
GW 14   13  -0.14000  -0.20000  8.000000  -0.14000  0.200000  8.000000  0.004763
GW 15   13  -0.14000  -0.20000  7.940000  -0.14000  0.200000  7.940000  0.004763
GW 16   13  -0.14000  -0.20000  7.880000  -0.14000  0.200000  7.880000  0.004763
GW 17   13  -0.14000  -0.20000  7.820000  -0.14000  0.200000  7.820000  0.004763
GW 18   13  -0.14000  -0.20000  7.760000  -0.14000  0.200000  7.760000  0.004763
GE  0
FR  0    1    0    0  470.0000  0.000000
EX  0    1    7    1  1.000000  0.000000                                        
XQ
RP  0    1  360 1000  90.00000     0.000     0.000     1.000 5.000E+03
RP  0  360    1 1000   -90.000     0.000     1.000     0.000 5.000E+03
RP  0   91  120 1001     0.000     0.000     2.000     3.000 5.000E+03
XQ
EN
Performance was slightly better with the reflector, however I did not receive any more channels with the reflector. Since the reflector adds some wind resistance load to the antenna, I opted to mount the antenna without the reflector and just the biquad antenna itself.

Code:
Reception results:

Channel   Biquad   Biquad+Reflector
  5.1        85%            87%
  9.1        73%            76%
 11.1        77%            79%
 17.1        65%            68%
 23.1        68%            75%
 41.1        60%            70%
 44.1        48%            54%
 57.1        58%            61%
 64.1        46%            53%
 66.1        57%            67%
Percentage reading is from my Aquos LCD TV. I also receive 25.1 and 36.1 but I don't watch these channels so I didn't record any measurements.

The antenna is connected to a distribution amp and splitter and drives two TV sets.
 

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Discussion Starter #38
UHF vs VHF performance

The biquad is primarily a UHF antenna that covers channels 14-69. However there is a bit of gain with a high SWR for the 7-13 VHF hi channels. I don't have any digital channels that transmit on VHF hi in my area, these channels are only analog. My tv does not have a signal meter for analog channels.

I can only show subjective quality. The picture ranges from good with a bit of snow like channel 11 (40 miles away NM 32db)-



to snowy but watchable channel 8 (57 miles away NM 6.5db)



channel 13 comes in great, but it's a local channel and the transmitter is only 8 miles away and I can get this channel very easy with any antenna.

I'll have to wait until the digital switch over when some of the digital channels will transmit on VHF hi to determine how well this antenna performs on the VHF hi band.
 
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