Long Wave and AM Broadcast interference

Discussions about everything to do with SDRuno
Post Reply
VK3MHZ
Posts: 42
Joined: Sun Apr 30, 2017 7:24 am

Long Wave and AM Broadcast interference

Post by VK3MHZ » Wed Dec 12, 2018 3:35 am

Gidday all;

I am pretty keen on long-wave DX, although right now I am struggling with AM Broadcast stations, for want of a better description - 'suprious images', since I don't know the correct technical term.

Example: 3CS (Colac) 83 Km (52 Miles) ESE 102º from my location, S9+30/-42.5dBm on 1134 KHz, is also quite strong on 336 KHz.

This is not the only AM station that I am getting images of on LW, just an example. Is there any way I can reduce, or even completely eliminate AM broadcast station images on the long-wave band (below 500 KHz)? Any help would be greatly appreciated.


System Specs:

Operating System
Windows 7 Home Premium 64-bit SP1
CPU
Intel Core i3 380M @ 2.53GHz
Arrandale 32nm Technology
RAM
4.00GB Single-Channel DDR3 @ 532MHz
Graphics
Intel HD Graphics (Acer Incorporated [ALI])
Audio
High Definition Audio Device

SDRPlay RSP2.
Antenna: HiZ input, 150 meter long wire.

Reason: No reason

Tech_Support
Posts: 499
Joined: Mon Jun 01, 2015 7:00 pm

Re: Long Wave and AM Broadcast interference

Post by Tech_Support » Wed Dec 12, 2018 6:41 am

Hello VK3MHZ
Have you tried low IF mode?

Please see the following applications note: https://www.sdrplay.com/docs/SDRplay_Op ... _MW_HF.pdf

Whilst this is predominantly aimed at the RSP1A, some of this is relevant to the RSP2 as well.

Sincerely

Tech_Support

Reason: No reason

glovisol
Posts: 662
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: Long Wave and AM Broadcast interference

Post by glovisol » Thu Dec 13, 2018 5:58 pm

Hi VK3 MHZ,

The incoming level of a MW broadcast station between -50 and -40 dBm is perfectly normal and most common, so we must live with it, but RSP class receivers are perfectly capable to cope with these levels while working in LW below the MW band, by using the LOW IF mode, as advised by Tech_Support. I am uploading three PC screens (taken with several MW signals with levels -40 to -50 dBm operating on the MW frequency band immediately above and not shown) as follows:

a) LW reception at ZERO IF with MW NOTCH FILTER IN - no spurious.
b) LW reception at ZERO IF with MW NOTCH FILTER OUT - very many spurious signals and most of them are higher order, not intermodulation.
c) LW reception at LOW IF with MW NOTCH FILTER OUT - no spurious at all!

So for even stronger signals you still have the notch filter in reserve. This is an RSPduo in operation as I do not have the RSP2.

Further know how on IIP3 and IIP2 here:

https://www.sdrplay.com/community/viewt ... f=5&t=3926

Cheers,

glovisol
Attachments
ZERO IF + notch.jpg
Figure a - LOW IF WITH NOTCH
ZERO IF + notch.jpg (200.93 KiB) Viewed 4789 times
ZERO IF no notch.jpg
Figure b - ZERO IF NO NOTCH
ZERO IF no notch.jpg (207.55 KiB) Viewed 4789 times
LOW IF no notch.jpg
Figure c - LOW IF NO NOTCH
LOW IF no notch.jpg (201.52 KiB) Viewed 4789 times

Reason: No reason

glovisol
Posts: 662
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: Long Wave and AM Broadcast interference

Post by glovisol » Thu Dec 13, 2018 6:50 pm

Sorry....I forgot to ask: how are you coupling the long wire antenna to the HI Z input? Are you using a transformer type balun? This is what you should be using anyway.

Reason: No reason

VK3MHZ
Posts: 42
Joined: Sun Apr 30, 2017 7:24 am

Re: Long Wave and AM Broadcast interference

Post by VK3MHZ » Fri Dec 14, 2018 12:43 pm

As I am using the HiZ input I am not able to use the MW notch.

The antenna is a 105m long-wire, to the positive terminal, N & G are bridged to ground (Earth stake).

Reason: No reason

glovisol
Posts: 662
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: Long Wave and AM Broadcast interference

Post by glovisol » Fri Dec 14, 2018 1:45 pm

1) I have just demonstrated yesterday with the PC screens (as also explained in the SDRplay white paper) that you can get rid of the spurious signals by using the LOW IF setting: go to the top left of the SDRuno main, click SETT. and in IF Mode select LOW-IF and put Decimation to 8 in the Decimation window: the interference will disappear. As I wrote, this works even if you DO NOT HAVE / DO NOT USE THE MW notch.

2) Direct coupling a 105 m long wire antenna (I myself am using a 135 m Beverage) to the P terminal, with N&G terminals to ground is extremely dangerous to the receiver (and to yourself, perhaps?): even a small indirect lightning transient could kill your RSP2 at any moment. Not only that, but you are probably bringing in a lot of noise which significantly reduces your system sensitivity. Please look at:

https://www.sdrplay.com/community/viewt ... f=5&t=3352

Where a lot of info is available, especially in the mid-posts of this long thread.

3) I am going to post a lowpass filter design (CAUER C05 15 40) which kills all MW stations and therefore radically eliminates the problem in the LF band once and for all with any kind of receiver, see:

https://www.sdrplay.com/community/viewt ... f=5&t=3943
Attachments
MW filter stopband.jpg
MW filter stopband.jpg (168.02 KiB) Viewed 4728 times

Reason: No reason

fotoralf
Posts: 38
Joined: Wed Aug 08, 2018 10:13 pm
Location: Western Germany, near Belgian border
Contact:

Re: Long Wave and AM Broadcast interference

Post by fotoralf » Mon Feb 11, 2019 10:32 am

glovisol wrote:go to the top left of the SDRuno main, click SETT. and in IF Mode select LOW-IF and put Decimation to 8 in the Decimation window
Given that SDRuno is still not available for Mac OS, how can this be replicated in GQRX or CubicSDR?

Ralf

Reason: No reason

ON5HB
Posts: 140
Joined: Sat Dec 29, 2018 1:07 pm

Re: Long Wave and AM Broadcast interference

Post by ON5HB » Mon Feb 11, 2019 2:51 pm

In CubicSDR it's no problem, select the IF-mode before you start the device.

Decimate is not needed to select, makes not that much of a difference.

I myself use Zero-IF where possible combined with RfNotch if needed.
Cubic-sdr.png
Cubic-sdr.png (87.65 KiB) Viewed 3648 times

Reason: No reason

kiheiman
Posts: 8
Joined: Thu Jan 31, 2019 8:32 pm

Re: Long Wave and AM Broadcast interference

Post by kiheiman » Wed Feb 13, 2019 1:27 pm

It is pretty easy to build out a band stop filter using the Mini-Kits bare filter circuit board. I built out one for 500 Khz to 1600 Khz for use with my Elad Duo and SDRPlay RSP1A. Please see attached sweep of the filter. A number of AM stations at my location have signal levels of -30 dbm. For specific frequencies, you could use the same board to build out a notch filter. Another option, using the same board, is to build out a low pass filter with a cutoff of 500 Khz.

Regards
Clint
W7KEC
Attachments
AM Band Stop Filter.jpg
AM Band Stop Filter.jpg (80.02 KiB) Viewed 3534 times
Last edited by kiheiman on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
Reason: No reason

Post Reply