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Author Topic: Major problem with nearby AM broadcast station  (Read 13238 times)
KE4JOY
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« on: August 14, 2013, 01:19:18 PM »

Just got a Yaesu FT-890 Radio works great but there is one major problem.

There is a nearby AM broadcast station. It absolutely swamps the receiver S9++ on all bands. No matter how much AF atten I put in its still there. It is so darn strong it actually causes the swr meter to react!

One thing to add. I was checking the receiver earlier today before a rain storm went through and I had to disconnect every thing until it passed... Okay I think I can finally get this thing on the air... but NO! I don't know if it was the rain or time of day, often AM stations change their patterns. I have no issue with my tube rig (HW101).

I kid you not the swr meter indicates a signal!  Angry

Update, I found the ATT button which does knock out the AM interference but detunes the receiver quite a bit. 12 db down I believe and no the IPO is not enabled.
« Last Edit: August 14, 2013, 01:59:22 PM by KE4JOY » Logged
K5LXP
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« Reply #1 on: August 14, 2013, 07:30:06 PM »

Try using a tuner inline even if you already using a matched antenna.  Often this will reduce the incident level of the AM station to a point where it's no longer overloading the receiver.  There are accessory BCB filters that do the same thing.

Mark K5LXP
Albuquerque, NM
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KD0REQ
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« Reply #2 on: August 15, 2013, 09:57:21 AM »

take the devil off the air... that is, at your receiver with a band trap filter.  anything else violates the law.

make sure you have a good common point ground in the shack with a nice low-resistance direct run to the ground rod.  use ferrite clamps around all leads.

hopefully this will make a dent in it.
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WX7G
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« Reply #3 on: August 17, 2013, 08:26:28 AM »

You found that using the transceiver attenuator solves the problem. Yes the receiver is less sensitive but should be fine for HF work.
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KE4JOY
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« Reply #4 on: August 22, 2013, 12:41:12 PM »

One other question...

I see that the AM station has a 'sign off' time according to fcc regulations. It also says it varies by month.

How does one go about finding out what that 'sign off' time is?
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WX7G
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« Reply #5 on: August 22, 2013, 01:50:23 PM »

Ask the station management?
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KE4JOY
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« Reply #6 on: August 24, 2013, 12:49:02 PM »

LOL I can see it now... "Excuse me but at what time do you cease transmission cause your bugging the heck out of me"  Grin

Did I mention it is a 10KW religious station?  Cheesy

I checked the old fashioned way and listened. They seem to reduce power at around 8:00 pm and go dark around 9:00 pm. I did not catch any 'announcements'.
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N5RMS
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« Reply #7 on: August 25, 2013, 01:31:26 PM »

I would be more worried about the amount of RF exposure to you and your family members !
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KX8N
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« Reply #8 on: August 26, 2013, 09:12:31 PM »

You could also ask other hams in your area if they are having the same problem. Could be that they've already come up with a solution you haven't thought of.
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WX7G
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« Reply #9 on: August 27, 2013, 06:45:35 AM »

Array Solutions has the solution in their BC band filter.

http://www.arraysolutions.com/Products/BCB%20RF%20Filters.htm
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WB2WIK
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« Reply #10 on: August 27, 2013, 11:03:23 AM »

One other question...

I see that the AM station has a 'sign off' time according to fcc regulations. It also says it varies by month.

How does one go about finding out what that 'sign off' time is?

What's the station's callsign?  You can look up their FCC license to determine almost everything about their operation including power or pattern changes after dark, off times, etc.

I would use the IPO, it should normally be engaged on the lower bands anyway.  I only turn "off" the IPO on 10-12-15m.  On 17m and bands lower in frequency, it helps the receiver work better.
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KD0REQ
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« Reply #11 on: August 27, 2013, 12:06:08 PM »

"sign off time that varies by month."  well, that says they are a modified daytimer, and have to shut down when the sky wave opens up.  weather bureau daily history sent to all and sundry, and on the noaa website for your area, will give sunrise and sunset times.  since they appear to reduce power at sunset, and then shut down a little later, that tells me the station they interfere with on the frequency is further west, and when their skywave starts, your local has to bank the fires for the night.

the license document will present the conditions.  look west on the same frequency for the shared frequency station, and when they officially hit sunset, your local will be predictable on its shutdown time. even a Google for "radio station xxxx khz" might find that.

you can, again, always call the station.  the "built on the Rock" jocks will have in their logs when they have to pull the plug, and if you get the station manager or engineer, they will probably tell you which station has the priority on the channel.

all of which is academic, you need an LC trap that heats up from their spew, rather than the front of your receiver.
« Last Edit: August 27, 2013, 12:09:55 PM by KD0REQ » Logged
KI5FJ
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« Reply #12 on: August 29, 2013, 08:15:11 AM »

Thomas (AK4HN aka KE4JOY??),
I am located about 7 miles away from a 5 KW (Daytime), 570 kHz station.
A 480 Ft Horizontal Loop Up 35 Ft into a IC-756Pro3 results in a 66 dB over S-9 (No Modulation).
Inserting a ATR-30 (T-Network) tuned for 75 Meters reduces the signal by a whopping 56 dB!
A L-Network ATU does not attenuate the signal as much.
When I listen to the weak 500 kHz experimental stations I use a Clinton Labs Band Reject Filter (540-1700 kHz).
73 Joe O NNNN
 
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KE4JOY
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« Reply #13 on: August 29, 2013, 03:41:04 PM »

Yea that's me  Wink

You are quite a ways further from the broadcast station than I am. I am about 1/2 mile of their antenna. I also noted some sort of parabolic looking array on top that is pretty much pointed straight at my qth. Though it looks way to small for the frequency.

Anyhow, my problem was pretty much solved through the ATT circuit which notches them out nicely. I just have to remember to be a little more generous on my signal reports. I have also learned how the IPO works and that does help some as well.

At least they cease in the nighttime.
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WB5ITT
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« Reply #14 on: September 03, 2013, 11:11:49 PM »

One other question...

I see that the AM station has a 'sign off' time according to fcc regulations. It also says it varies by month.

How does one go about finding out what that 'sign off' time is?

DOES this station have only daytime authorization?? If so, it usually signs off at local sunset OR f protecting a station to the west, the sign off time is sunset at the station to the west...You could build a filter to kill their signal as your front end is overloading from the AM...(any modern HF rig with an attenuator button has that issue on STRONG signals...they make the front end wide enough but not sensitive unless the preamp is on....kinda of a Catch 22 situation...) A notch to kill the amount of AM signal should be capable of being built...since it would be notching the AM station, it should not affect normal ham operations...I'd go for a 5 sections HP filter or a T notch to ground to shunt the AM signal...
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