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Author Topic: Reduce noise floor on top-band  (Read 354 times)

XW0LP

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Reduce noise floor on top-band
« on: March 14, 2021, 06:02:33 AM »

In an effort to reduce the QRN level on top-band, I used my RTL dongle to view the received signals from my quarter wave vertical antenna, using USB mode (I usually operate FT8).

Here's a screen-grab:



The 1842 KHz strong signal is ???  (I've alrteady been around my house with a receiver and switched off electrical appliances in turn - that signal remains).

Notice the constant signals every 5 KHz.....

My noise floor at 1840 KHz is only about -65dB.  How to improve this? (is it possible)?

I appreciate your suggestions :)
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G0BDE

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Re: Reduce noise floor on top-band
« Reply #1 on: March 14, 2021, 06:18:24 PM »

I wound the power cable to a multi power block with a seven inch by three quarters of an inch medium wave, I think, ferrite rod.  This has reduced the general hash on 160m two and a half S points! It wasn’t expected at all and well pleased I tried it.

I sometimes use a Wellbrook Loop on a rotator in the loft for some noises that I believe are not generated in the house to null them out.

I have now also wound the leads of all power cubes onto snap on ferrite blocks.  It doesn’t seem to have lowered the signal any appreciable amount but it has improved the received noise a little-kind of smothed it.
It is most noticeable when I turn on and off the security cameras and recorder plus a 14 inch monitor. This effort was done in the last couple of days.

Hope this gives you some assistance and ideas.   
« Last Edit: March 14, 2021, 06:26:42 PM by G0BDE »
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XW0LP

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Re: Reduce noise floor on top-band
« Reply #2 on: March 14, 2021, 08:07:17 PM »

Thanks for the advice.  I already have toroids on my rig power cables :)

I just bought a heavy-duty 12 volt motorcycle battery and charger.  Tonight, I will switch off the electricity to the whole house and run the rig off the battery and check the received signal with my SDR and laptop (powered by its battery also).  Luckily, I live alone and can power everything off if needs be!

I know that the LED street light outside my house generates 'hash'.  That's why it met with an 'accident' a few months ago.  Sadly, the electricity company did a routine check a few months later and repaired the damaged power supply cable to that light....
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G0BDE

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Re: Reduce noise floor on top-band
« Reply #3 on: March 15, 2021, 03:02:40 PM »

The battery is a good idea and will be interesting exercise. I have an LED street light about forty feet from my aerial but haven’t noticed any improvement when it goes off at midnight though.  The noise problems will only get worse as time goes by with new domestic gadgets coming on stream all the time - unfortunatly.  Good Luck.
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XW0LP

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Re: Reduce noise floor on top-band
« Reply #4 on: March 15, 2021, 04:40:50 PM »

Well, I did the battery experiment last night.  I powered my rig from the battery, switched off the mains electricity at the switch where it enters the house, switched off the UPS that powers my internet routers and ....... no change!!

My noise level on top band is consistently at a tiny bit under S9 on my rig :(\

The receive antenna pre-amp has arrived at the courier office in town.  I'll collect it later and see if that can help.

So far, not good...
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WB8VLC

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Re: Reduce noise floor on top-band
« Reply #5 on: March 16, 2021, 10:05:12 AM »

Good luck but I suspect its not going to be as easy as you think it will be.

It took a historical ice storm and the replacement of over 1000 miles of power lines, thousands of transformers, thousands of new connections and poles and other items in our power grid replaced here in Northwest Oregon before my noise level dropped on HF.

From 160 to 60 meters it dropped from S9 plus to around s5,  from 40 to 20 meters a drop from s7-s8 down to s3-4 and above 20 meters s6-7 down to around s2-3.

In the past even when operating from a battery my noise was still excessive but now with the entire power grid infrastructure in northwest Oregon having been replaced with new equipment HF radio is similar to what I remember back in the 1970's and 1980's.

It appears that the power grid infrastructure world wide is based on 60 to 75 plus year old equipment that has been milked along over the years with various band aides and such.
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XW0LP

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Re: Reduce noise floor on top-band
« Reply #6 on: March 16, 2021, 06:01:39 PM »

I finally received my parcel from DX Engineering.  The Signalink interface is A welcome replacement for my broken digital interface :)

As for the 160/80 receive antenna pre-amplifier, I had high hopes, and connected to my pennant antenna.  The result?  Same as before ==> deaf as a post and no signals received.  I switch back to my quarter wave vertical (transmit antenna) and stations are received.  Oh well, I will leave the preamp in my receive chain from my transmit antenna, because at least it gives me a variable preamp gain control....

Realistically, the only way that I can improve my station is to relocate to an electrically-quiet environment in Laos, with plenty of land to put up beverages, 4-squares etc etc.  That is not an unrealistic option, but I do need to have a fast internet connection for my online teaching, and such a fast connection is usually not something available 'in the sticks'.  However, Elon Musk's Starlink project is expected to offer such internet speeds (actually much faster than I need!), to rural locations in Asia by the end of 2021.  So if Starlink becomes an option out here, then moving house also becomes an option for me :)
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