Canadian TV, Computing and Home Theatre Forums banner

721 - 740 of 772 Posts

·
Registered
Joined
·
471 Posts
My Terk HDTVa amplified antenna has both the UHF and the rabbit ears built in (it is a silver sensor clone with the rabbit ears). It works quite well with VHF high and UHF for an indoor antenna.
 

·
Registered
Joined
·
1,218 Posts
I emailed another online retailer my TV Fool Report which appears in post Number 715 and they emailed me back saying they would recommend the Channel Master CM-3000HD Smartenna. I looked it up online and it say its only good for VHF High and it doesn't mention anything about VHF Low.
 

·
Premium Member
Joined
·
1,127 Posts
That is another bad answer.

You are getting bad answers because your situation is very unusual. The techs that you ask don't have the experience to give a good answer for your location, which requires an indoor antenna for VHF-Low channels 2 and 4.

The only antenna that you can buy for your reception problem is the Winegard HD7000R. It comes with extensions to make the elements longer for VHF-Low channels if needed.

https://www.google.com/search?biw=911&bih=397&ei=28q3W6z9BonD0PEP--CYiAM&q=Winegard+HD7000R+site%3A.ca&oq=Winegard+HD7000R+site%3A.ca&gs_l=psy-ab.3...7116.15933..16177...0.0..0.185.1413.0j9......0....1..gws-wiz.......0j0i71j0i22i30j33i160.WFAU50aqY6A

I have finished making a DIY indoor channel 3 antenna and will post the photos soon. Maybe you can make one too.
 

·
Premium Member
Joined
·
1,127 Posts
Here are some photos of the Channel 3 antenna that I made. I bought the wire and 1 x 2 select pine boards at Home Depot. I already had the yardsticks, terminal block, and balun.



I clamped the 6' mast to my platform cart:



 

·
Premium Member
Joined
·
1,127 Posts
Here is a closeup of the terminal block:



This shows how the wire goes around the end. I used masking tape instead of nylon clamps to hold the wire:



The antenna can be taken apart for storage:

 

·
Premium Member
Joined
·
1,127 Posts
I next made some measurements of the electrical noise level to find out how strong a signal would need to be for good reception with my indoor antennas.

Noise level on channel 3 with channel 3 folded dipole: -67 dBm
Signal would need to be at least -52 dBm to allow for the minimum required SNR of 15 dB
Your report lists your signals at about -33 dBm, 19 dB stronger; looks possible

The tuner noise is irrelevant because it is buried in the ambient noise at -100 dBm

Electrical noise on VHF can come from CFL lamps, LED lamps, electric motors, switchmode AC adapters like for laptops and battery chargers, hair dryers, and ignition noise.

Noise on channel 10 using folded dipole of GE 34792 indoor/attic antenna: -91 dBm
Signal would need to be at least -76 dBm to allow for the minimum required SNR of 15 dB

Again, the tuner noise is irrelevant because it is buried in the ambient noise at -100 dBm

Noise on channel 36 using UHF yagi of GE 34792 antenna: -106 dBm, which is the thermal noise floor for a 6 MHz TV signal
Signal would need to be at least -85 dBm to allow for the tuner noise at -100 dBm and the minimum required SNR of 15 dB

So, you can see why there aren't many TV channels on VHF-Low 2-6, because of the high noise level from electrical interference. There are three advantages to VHF-Low: Not much transmitter power is needed for the same coverage area, the signals can make it over rough terrain easier, and the building penetration signal loss is low.

There aren't any VHF-Low channels in my area, but I will try to make a simulated reception test with the channel 3 indoor folded dipole antenna.
 

·
Premium Member
Joined
·
1,127 Posts
72 inches isn't quite wide enough, but it might work; give it a test.

You will also need a 300 ohm to 75 ohm matching transformer balun.
 

·
Premium Member
Joined
·
1,127 Posts
This chart shows why it is more difficult to receive VHF-Low channels because of the higher noise levels on VHF. Stronger signals are needed to overcome the noise:

 

·
Premium Member
Joined
·
1,127 Posts
Earlier post mentioned a FM Dipole Indoor Antenna. I found this one on Amazon it is 72 inches wide and 60 inches high. It looks similar to what rabbit73 built. Here is the link: https://www.amazon.ca/gp/product/B000EIOQBM/ref=ask_ql_qh_dp_hza
The description on Amazon (and Walmart) is not correct. Amazon says:
5-Ft Center Lead With 6-Ft Span
but it is really about 5 ft wide with a 6 ft downlead.







Half of the dipole is 29"; the dipole is 58" wide

Width in inches = 5540/freq in MHZ
so
freq in MHz = 5540/Width in inches

5540/58 = 95.5 MHz

The FM band is 88 to 108 MHz, so the PET10-8110 antenna is cut for the center of the FM band.

I measured the DC resistance of the antenna, because it is a continuous loop of wire. It measured 7.8 ohms with my Fluke 115 DMM. The resistance is higher than expected because they used very thin wire.

You still need to try it to see if it will work for you on CH2 and CH4. It might even work on CH9; mine worked on 7 and 13.
 

·
Registered
Joined
·
1,218 Posts
I have purchased the above antenna from amazon Canada. It has been shipped but I have not received it yet. I will be happy with channel 2 and 4. We have been getting a lot of rain lately and my Bell Satellite dish has been going down a lot lately.
 

·
Premium Member
Joined
·
1,127 Posts
I made some measurements to compare the gain of my channel 3 folded dipole to the gain of the PET10-8110 FM Dipole on a channel 3 analog signal.

I don't have any VHF-Low transmitters in my area and I don't have an 8VSB modulator. i used the channel 3 output of a Channel Master 7004 converter box as a test signal and measured the strength of the video carrier with my Sadelco signal level meter.

I set up one of my channel 3 folded dipoles and connected it to the output of the 7004. Then, I setup another one of my channel 3 folded dipoles about 8 feet away and measured the strength of the received signal. It was +14 dBmV (-35 dBm).

Next, I substituted the PET10-8110 FM Dipole as the receiving antenna. The received signal measured +2.5 dBmV (-46.5 dBm).

My channel 3 folded dipole has 11.5 dB more gain than the PET10-8110 FM Dipole on channel 3. I don't know how much difference that would make at your location as far as being able to receive 2 and 4.

I inspected the center and end connections of the PET10-8110 FM Dipole.





The solid copper wire for the PET FM Dipole is very thin and fragile. Usually, the twin lead wires of a folded dipole are twisted together and then soldered for greater strength. The wires of the PET FM Dipole were just touched together and then soldered.

Besides making the PET dipole fragile, the thin wires reduce the effective bandwidth, making it more difficult to cover from 2 to 4.

If you have any doubts about the wires in your PET FM dipole, you can check for continuity with an inexpensive ohmmeter like the Elenco M-1000 DMM.
https://www.amazon.com/Elenco-M1000E-Multimeter-M-1000/dp/B0015126L4

or the GB GMT-318 analog meter.
https://www.amazon.com/Gardner-Bender-GMT-318-Multimeter-Function/dp/B00291X79O

https://www.homedepot.com/p/Gardner-Bender-14-Range-Analog-Meter-GMT-318/202867892

My PET FM Dipole measured about 8 ohms between the two terminals that connect to the balun.
 

·
Premium Member
Joined
·
1,127 Posts
I have purchased the above antenna from amazon Canada. It has been shipped but I have not received it yet. I will be happy with channel 2 and 4. We have been getting a lot of rain lately and my Bell Satellite dish has been going down a lot lately.
Please let me know the results of your test with the FM Dipole antenna. If it doesn't work for channels 2 and 4, I can suggest something else to try.

Best regards,
rabbit
 

·
Registered
Joined
·
1,218 Posts
FM Dipole Antenna was received today from Amazon. I hooked it up and was able to receive channel 9 with a 100% picture quality. I didn’t get any picture at all on channels 2 and 4.
 

·
Premium Member
Joined
·
1,127 Posts
Thank you for the report of your test with the FM dipole; sorry to hear that it didn't give you 2 and 4.

There are two factors involved. The antenna might not be long enough to give the gain that you need for 2 and 4. My test of the FM dipole showed that it had about 11 to 12 dB less gain than a folded dipole 88" long using THHN 14 gauge wire.

The other factor is the noise level, which is very high on channels 2 and 4 from electrical interference. Your indoor antenna needs to be located where the noise level is as low as possible.

My tests have shown me that the noise level with the FM dipole is also lower by about the same amount as the signal, giving the same SNR. This means that the FM dipole might have enough gain for the signals, but there isn't enough difference between the signal and the noise.

I made some more tests yesterday to compare tbe 88" folded dipole with the FM dipole, using the channel 3 output of a Channel Master converter box as a test signal and my Sadelco 719E signal level meter. The meter has a speaker so that I can hear the sound of the noise and the video carrier of the signal, in addition to being able to measure their strength. I used the meter on the left:



88" folded dipole
signal: -3 dBmV (-52 dBm)
noise: -13 dBmV (-62 dBm)
The signal is 10 dB stronger than the noise. A digital signal needs to be at least 15 dB stronger than the noise for reception. I could have used a stronger test signal to make the difference greater than 10 dB, but it didn't matter for this test to compare the two antennas for gain.

FM folded dipole
signal: -15 dBmV (-64 dBm)
noise: -26 dBmV (-75 dBm)
The signal is 11 dB stronger than the noise with the FM dipole.

The 88" folded dipole has 12 dB more gain than the FM folded dipole.

There are two thngs you can try:
1. Build an 88" dipole like I did
2. Try to find a location that has less electrical noise interference

The second one will require trial-and-error by you because you don't have a meter to measure the noise. You can suspect interference from CFL and LED lamps. You can also use a portable radio operating on batteries that will tune the AM broadcast band to hunt for noise sources. Tune it to a vacant frequency at the low end and at the high end of the AM broadcast band. Sometimes a high noise level on the broadcast band will also indicate noise on VHF channels. It doesn't need to be an expensive radio. I use a Jensen MR-550 AM/FM Portable radio. Use it on AM not FM; it works better on AM to hunt for noise. The built in AM loop stick antenna acts as a direction finder.



Maybe you could also set up a temporary antenna outside as a test.

What balun did you use to connect the FM dipole to your TV?
 

·
Premium Member
Joined
·
1,127 Posts
That should be OK. If you need to move the antenna further away from the TV, you could use a length of coax and an F-81 adapter.

 
721 - 740 of 772 Posts
Top