Baffled by HUM in the Zowaysoon Antenna

Obviously, something has changed and if this is caused by the storm it may not be a problem with your FM system.

Many times hum on an FM signal results from the signal being picked up by wall wart powersupplies and due to the non-linear components inside the FM can be radiated with hum imposed.

Try unplugging wall warts around your home.  Maybe one was damaged by the power surges/cycling.

Neil

Since it still works with the factory antenna, I am wondering if you had moisture get into the feed line?   Might be worth checking.  I know you checked for damage, but it is a thought.

Note that those Sainsonic FM transmitters have a bogus FCC ID number printed on them and any claims of them being Part 15 approved are false. Even on the low power setting, they greatly exceed the FCC Part 15 FM signal field strength limit.

I know the issue is with the antenna per your description, but when hum appears suddenly out of nowhere, my initial thought is a filter capacitor in the power supply pooped the bed. Have you swapped PSUs to the transmitter? 

I want to suggest a couple of power-related possibilities first...If there is a way to apply 12VDC operational power to the unit with a battery, do so; see if there is hum when powering the transmitter that way.

Per the previous suggestion, go around and unplug power blobs all around the house one at a time, while monitoring your signal... especially switching power supplies, which coat the place with RF like a flea bomb. One of them may have gotten knocked assways.

Does the hum persist when the audio input device (player, computer, phone et al) is removed? Check the cable, or just replace it outright.

Are you plugging into an audio playback device (like a phone or tablet) that has a four-pin jack, but with a three-pin TRS cable? Those devices feed DC power to drive the electret microphone found in headsets, and you might be pumping that voltage into your transmitter.

Anyway, that's the power-related crap. Let's look at the antenna.

You said the coaxial cable appears undamaged. Appearances can deceive. Lightning, even a good distance away, can induce hundreds or thousands of volts in any long piece of wire and poke a hole in a cheap dielectric. If you detach it from both devices, let one end float and hit the other end with a multimeter, do you show an open circuit, a dead short, or a little bit of resistance? If you get #2 or #3, replace the coax.

Do you have metal siding on the house? If so, use standoffs to move the cable away from the outside wall. And what's of the other side of the wall all the way up to the roof? Anything that would set up a strong field, like a freezer motor, an air conditioner, a bunch of CFLs, etc?

If nothing has shaken loose by now, try a temporary substitute antenna. Cut about 38" of wire and just hang it where your Zowaysoon should go. Check your signal.

Finally, it may be an SWR problem that only just revealed itself. Maybe the transmitter was never meant to drive a cable of that length without some retuning, in spite of what the instructions may say. Drop a note to Sain Sonic and hope someone answers.

Lot of material here. Hope some of it is useful. Good luck.

Oh... and Keep It Legal.

Hi Gassoff: Here is some ideas.

1) Before getting into hobby you should read all the rules and understand.

2) Then purchase the test equipment that is needed for your station.

3) Then after purchase bench test all your station equipment before use.

So if you need to send back for replacement if needed.

You should bech test your antenna after receiving it with a MFJ-259 meter to make sure its fine and have it pretune before a full install.

You should have a dummy load and swr and power meter for your transmitter to make shure its fine as well.

The reason I have said this is

The rubber duck antenna that comes with the sainsonic ax-05b is trash.

I checked with my MFJ-259 and found it works in 141MHZ band with a swr of 1.2.

When I checked the rubber duck antenna in the FM band it had a Swr of 3 to 5

And the load resistance varied as well.

I brought this up to sainsonic and they said they NEVER checked the antenna !

SO THIS WHY PEOPLE NEED TEST EQUIPMENT, IT'S FOR YOUR OWN PROTECTION.

I THOUGHT I LET YOU KNOW OK.

good luck and enjoy the hobby

Station 8

I had a similar experience with a 2 meter rubber duck. Howver, when I attached a 19 inch piece of wire to the analyzer the S.W.R fell right in line.

I really appreciate all the replies.  I was able to get the hum out, and if I am being perfectly honest with you all, I do not know why it is gone.

Even though, all the connections seemed tight to me at the time, I got on the ladder, and unscrewed every location where the coax was attached, and screwed it back on.  I did the same thing at the top where you screw on the length of antenna that best matches your FM frequency.  

I did not find any water anywhere.  I had used zip ties to guide the coax down from the roof along an aluminum downspout on the way to the basement.  I detached those, and ran the coax straight down the brick side of the house.

And just to be safe, I removed a cordless drill charging station that was in the same room as the transmitter that had a wall wart type of charger.

Plugged it back in, and the hum is gone!  Again, not sure which thing it was that actually did it, but I read and appreciated everyone's consideration to my situation.

In regard to it being legal, I know that it is not.  In fact, using the zowaysoon antenna in itself is enough to violate the rules, because Part 15 requires the antenna attached to the back.  It is also true, that even with the whip antenna attached to the back, this is a Chinese transmitter with a fake FCC approval stamp on it.  All this I know.

That said, I am in an area where I will not be bothering anyone or any signal.  If not leagl, at least respectful.  I'm only trying to cover my house, but I do get about three houses near me, and can hear it most of the way when I walk to dog.  

The only thing being broadcast is classic rock with an emphisis on deep tracks.  So, there is nothing hateful, dirty, or offensive being put on the air, and my signal is as far away from existing stations as possible.

But I have accomplished what I needed, and that was to move the transmitter away from the computer which is "studio" and clear up the signal in my microphone and speakers.

Again, thanks for the quick replies, and the warm welcome.

Just to open myself to ridicule, Part 15 rules are to mitigate interference based upon technical and physical criteria.  If you are not causing interference I see no problem.

Now that is not to say I advocate purposely violating the rules, just that rules can't mitigate interference that doesn't exist.

If you are causing interference and you are non-compliant then you don't have a leg to stand on.  And even if you are compliant and causing interference you still don't have a leg to stand on so it really doesn't make much difference does it.

The most persistent interference on my dials comes from the programming on local licensed stations.

For me, a radio is a device that can tune away from the interference of legally ugly watt wasters.

A small whisper transmitter on some blank channel redeems the receivers and gives them a positive use.

Part 15 radio is my lord and saver.