feedback from 40 meter diapole to stero speakers

Everything is grounded but the stereo speakers in the next room hum when ever I transmit on the 40 meter band on a diamond dipole antenna. The swr is low and the antenna seems fine as long as I turn off the stereo.

 

Sounds like "RF in the shack." What kind of antenna do you have, and where is the feed point relative to the speakers?

NVM....Dipole antenna.

 

http://www.arrl.org/radio-frequency-interference-rfi

The usual stuff to try....
-Reduce power
-Change bands
-Put Mix 31 chokes/toroids on speaker leads, closest to speaker, use as many turns as possible; probably 3-5 turns minimum required. coil up excess leads; shorten leads
-1:1 Current Balun at antenna feedpoint
-1:1 balun/isolator on feedline at shack entrance
-Housekeeping: Separate coax, control lines, leads, coil up excess
-Re-orient antenna
-Move antenna further away, elevate

b.

 

Do a little investigation via google into "common mode" current. You have RF where you don't want it to be.
"Grounds" effective for RF are a challenge and your SWR is not relevant.

Also investigate "common mode choke" which is likely a way to limit your common mode current.

 

It could be common mode problems on your coax bringing RF transmit signals back to your home but it could just as easily be radiated RF transmit power from the antenna if the antenna happens to be close to your home. A good common mode choke (aka 1:1 current balun) at your dipole feed point could help if it happens to be common mode on your coax but if it's just power radiated off of your antenna (transmit antennas do transmit RF signals after all) then your best bets are either to move the antenna further from the house if that's possible or to use shielded, twisted speaker cabling and or choking the speaker cables with common mode chokes.

Good common mode chokes for speaker cables can be made by winding the speaker cables through ferrite toroid cores or through clamp on ferrite cores. Good mixes for RFI choking include mix #31, #43 and #61 or #73. Don't buy mystery ferrite materials from eBay or otherwise, a lot of ferrite chokes are intended for VHF/UHF use don't work well for HF choking. Here's a good source for good toroid cores and clamp on ferrite suppression chokes: https://www.kf7p.com/KF7P/Ferrite_chokes.html

Shielded, twisted pair or twisted-shielded speaker cable can also help in terms of reducing RFI pickup on the speaker cables themselves. Basically the speaker cables themselves can act as receive antennas and any active junctions in the stereo amplifier or in the speakers themselves (e.g. active, powered speakers) can act as crystal radios and detect relatively strong RF signals. Running twisted pair and or shielded speaker cables can help reduce the signals they pick up from your transmissions. Don't fall for the crazy expensive audiophile cabling (e.g. 'oxygen free') but twisted-shielded cable is good insurance against the speaker cables themselves acting as antennas, IOW something like this: https://www.cdw.com/product/c2g-18-...ded-speaker-wire-bulk-speaker-cable-1/2711583

 

RF may not be getting into the speakers directly. In my case, RF was getting into the stereo through an external device (equalizer). Once I placed toroids on the input line to the stereo, RFI stopped. These days, you can plug the world into a stereo, so do a little troubleshooting by unplugging each device one at a time and run a test.

 

Modern audio systems can be incredibly sensitive to RF. I once received a WRMI broadcast over some computer speakers. WRMI is hundreds of miles from my location and the signal had propagated off the ionosphere!

 

Me thinks you might be barking up the wrong tree. I have fixed at least a dozen local CB'ers and hams with the exact same problem. Do you have a SUB WOOFER?

If you do put a choke on the RCA cable between amp and sub. Or get smart and use optical or digital audio and all that goes away. I had the same problem along with a dozen other friends around town. It is just Brute RF getting into signal cables that uses ground as a conductor.

Also if you have anything like a turntable, video recorders or anything that outputs a analog audio into the stereo inputs using RCA connectors. Ground suks and why it is not used anymore.

Easy to find and test. Just disconnect inputs and see which one is the offender. Identify and then use snap-on ferrite rings

 

I have been fighting a similar problem and ended up researching ferrites from https://www.fair-rite.com/ Their web site provides excellent selection tools and then allows you to easily comparison shop stocking distributors. I use Digi-Key.

Be sure to check several sizes and mixes that would suit, as pricing seems to vary quite a bit from PN to PN/ different mixes and different internal diameters. Not sure why. Maybe different mixes cost different amounts to manufacture and some PNs have higher production volumes.

 

Using ferrites to "choke" low impedance lines like the 4-8 Ohm speaker feeds often doesn't work well at all. The current is too high (in the wiring) and the wiring creates long, effective antennas.

It might work in some cases, but I wouldn't bet on it.

I once had a similar problem with a standard off-the-shelf SONY 5.1 surround sound system here. Nothing whatever to do with "common mode" current on the transmission line or anything like that, just pure RF radiated by my antennas, which in this case was a 40/80/160m trapped inverted vee on my tower, with the closest down leg about 75 feet away. Still too close. On 80m, 75 feet is very close.

I tried choking speaker leads and all that: Nada.

Found the problem, experimentally: The system "receiver/player/amplifier" also had a magnetic head because it had an integral VHS player/recorder and that actually turned out to be the entire problem. Since VHS is going the way of the Dodo, newer systems may not have this (this was about ten years ago) and just have BluRay recorders/players. But this one had both.

I had to take it apart and find the incredibly tiny wires that connected to the heads. They must have been about #30 AWG or so, very thin. But, easy to find and easy to unsolder. I added a couple of slip-on ferrite beads over those wires and tried again.

Problem completely gone.

Easier to choke RF problems at "small signal" stages then at "100 Watt" stages.