Antenna options

[rabbit73]

By finding the source like MikeBear did. Rather than repeating everything, please read his thread.
http://forum.tvfool.com/showthread.php?t=15701

It might be your problem, or not. Make some tests with AM receivers for the broadcast band and for VHF if you have a receiver that covers the aircraft band.

[sl1982]

The best I have is a clock radio. Does it matter what frequency its set to in the AM band?

[rabbit73]

I use a battery operated portable radio that covers the broadcast band, 540 to 1610 kHz. Tune to the low end of the band where there are no stations, then try the high end. The ferrite stick antenna in the portable radio has a directional effect.

I have a VHF-Hi channel that is marginal. I can receive it sometimes when the SNR is 15-16 dB. When the noise level is higher, I can't receive it because the SNR is less than 15 dB. I am able to measure the signal and the noise in an adjacent unused channel, and my Sony TV gives me the SNR in the Diagnostics Screen. My old SLM (signal level meter) has an AM detector for the audio so I can hear the signal and the noise. It's the meter on the left; the newer meter on the right can also measure noise and signal.



A car radio also covers the broadcast band. When I drive around town with the radio tuned to a frequency where there are no stations, I can hear the noise get louder when I get near power lines, especially the big high tension lines. This test doesn't work with the FM band on the radio, because FM is designed to reject noise.

The broadcast band is much lower in frequency than the VHF aircraft band (118-137 MHz) or the VHF TV band but often if you hear the noise on the broadcast band it is also on VHF TV frequencies. It is worse on VHF-Low than VHF-High.

http://www.arrl.org/files/file/Technology/HANDSON.pdf

[sl1982]

Ok so interestingly enough it is my pc causing emi. shut it off and the signal goes from 50-50 to 65-70. Only problem is i am not sure what component it would be.

[rabbit73]

Thanks for the report. I think you have found the source, but there could be other sources. The component that usually causes the interference is the power supply. The power supplies now being used are called switch mode power supplies (SMPS), or "switchers" for short. They are more efficient than the older linear power supplies but have a tendency to produce a lot of EMI unless they have the proper filters installed.

https://en.wikipedia.org/wiki/Switch...e_power_supply

If your PC is a desktop, the power supply is inside. If you have a laptop, the AC adapter is the usual source and it is sometimes possible to buy an adapter that is less noisy like MikeBear did.

Some people modify the power supply in their computer and install extra filters, but that is beyond the ability of most users.

http://ka7oei.blogspot.com/2012/12/r...racket-rf.html
http://ka7oei.blogspot.com/2014/08/c...ing-power.html

I don't know of a source of low noise power supplies for a desktop, but this one claims "Premium EMI/RFI power filtration provides low noise and ripple for stable power delivery."
http://www.newegg.com/Product/Produc...w&gclsrc=aw.ds

EMI can be radiated through the air to your antenna or conducted through the power line, or both.

If the interference is radiated through the air the cure is to increase the distance between the source and the antenna.

If the noise is conducted through the power line, sometimes using a different circuit helps. An AC line filter can be installed near the source, and one can be installed near AC operated equipment that is being affected.

http://www.repairfaq.org/REPAIR/F_CompRFI.html
from the ham radio viewpoint

[sl1982]

Thank you for the info. I built the computer so i am familiar with the power supply (desktop). Its was not a cheap one so i am suprised that it would be causing so much emi. As for other sources of interference in the house i can pretty much rule thise out as i shut off every other breaker except the one the amplifier and hdhomerun are on. The computer and the amplifier are on seperate circuits already and the computer is about as far away from the antenna as i can make it. Short of putting it in the basement.

Edit: putting the side of the computer case on did seem to improve things a bit. So it is probably radiated through the air. Can the amplifier itself pick this up? They are in adjacent rooms.

[rabbit73]

what amplifier?

[sl1982]

The antenna amplifier. Preamp i suppose its called.

[rabbit73]

Ah, yes the Antennacraft 10G212. That has a plastic case doesn't it?

[sl1982]

Yes it does

[rabbit73]

Preamps with a plastic case don't reject EMI as well as preamps with a metal case according to ADTech, and yours has two plastic case units. It does help that your coax is grounded.

Did you try the FM filter yet? We are now on page four and I'm having a hard time keeping track.

[sl1982]

Not yet. I am still waiting for the shipment. I do have some metal foil tape i could put on the case of the unit, if that would help.

[rabbit73]

That might be an interesting experiment with aluminum foil, but don't leave it on too long because of heat buildup.

It could be getting into your HDHR. Can you try a test with antenna into a TV tuner, eliminating the HDHR?

[sl1982]

I did that into my panasonic tv. Pretty much the same

[rabbit73]

Was the computer off or on then during the antenna directly to Panasonic without HDHR test?

You need your computer when you use the HDHR don't you?

[sl1982]

Well this is a different computer. So it isnt needed for the HDHR. And the computer was on when i tried the tv directly.

[rabbit73]

If that computer is in use while someone is watching TV, then you will need to find a way to reduce the EMI that it is creating. Maybe one of these ways:

1. AC line filter for computer
2. Power supply with better filtering for low EMI
3. Better shielding for computer case
4. Is the monitor creating EMI?

Does the computer have a 3-wire power cord that has the grounding pin connected to a properly wired 3-wire AC receptacle?

[sl1982]

So i got my FM traps and they did not help the situation out at all. I even put three of them inline with no appreciable change. It looks like we have narrowed this down to the emi interference. I am going to have to do a few more tests. I am going to put foil on the window of my case and see if that improves it. I will also see if it is the monitor. Failing all that i will have to spend some money on line conditioners. If that doesnt work i guess i will have to shut down the computer while i am watching fox.

[rabbit73]

I'm wondering if a low EMI power supply for the computer, or an AC RFI line filter for the computer would help.

How about a Faraday Cage for the computer?

Just kidding, that would be an extreme solution.

[sl1982]

I will build a faraday cage if need be.... assuming my wife lets me. I was looking into emi/rf interference mitigations and i came across this
Cleansweep 10A

While i think something like this may work i cannot find any prices on them. Another option could be one of these:
ISOBAR6 Ultra