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Old 11th Feb 2020, 12:58 am   #1
Tony1951
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Default Horrible distortion at times on 198KHZ Radio4

I hope this is the right place for this post.

I am running a KIWI SDR networked HF radio and have been listening to 198KHZ long wave and comparing it with other LW transmissions. At times the signal is clean enough to be acceptable, but now and again, the signal deteriorates horribly into a sort of Donald Duck squawking.

I live in an area which is noted for poor reception - the Tyne Valley near Brampton and it is served by both the Droitwich and Burghead and Westerglen.

My question is about whether there is something horrible going on at the source of the signal, or whether selective fading may cause some kind of bad interaction between the different signals arriving at my loop on the ground antenna in the garden.

View of spectrum:

https://drive.google.com/file/d/18Ys...ew?usp=sharing



The signal is fairly strong, varying between about -88dbm and -70dbm depending on the time of day. The radio is networked and can be heard here at this link, although only one visitor at a time can be accommodated. You can tune around by using the interface and can look at the spectrum by moving in on the frequency using the interface features.

The issue is intermittent, so you may not find it happening if you visit.

http://ne499lr.proxy.kiwisdr.com:8073/

I have compared other similarly powered long wave signals, such as RTE on 254Khz and Luxembourg and they sound clean enough over long periods and are not subject to this distortion at all, even though they may fade over time.

Last edited by Tony1951; 11th Feb 2020 at 1:12 am.
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Old 11th Feb 2020, 8:50 am   #2
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Default Re: Horrible distortion at times on 198KHZ Radio4

‘Donald Duck squawking’ exactly describes what amateur radio SSB (single sideband) transmissions sound like on a receiver which doesn’t have a BFO/Product Detector. I don’t know a thing about SDR, but ordinarily, the phenomenon that you are experiencing is what happens when nearby amateur radio transmissions cause RFI/TVI - radio frequency interference/TV interference.

That would be my guess, but quite where, why and how it’s happening is anyone’s guess. The intermittent nature of the interference fits the pattern of an active radio amateur (there are still a few!) operating on SSB at various times of the day. There was a time many years ago, when OFCOM’s predecessors had reasonably local engineers who would investigate such complaints, but not any more.

If other SDR radio users not local to you can hear it, the source it would seem to be not local to you.

Someone ‘further up the food chain’ on the forum might have other ideas!
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Old 11th Feb 2020, 9:22 am   #3
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Default Re: Horrible distortion at times on 198KHZ Radio4

Step 1 is to listen to 198kHz with a 'normal' superhet receiver.

Do you hear the same thing at the same time as you hear it on your SDR?

If so, then it is probably something actually on or very close to 198kHz.

If not, then it is probably something strong (nearby) on a different frequency that happens to hit an image (nyquist alias) of your SDR, or it may simply be strong enough that your receiver overloads on it and the signal will appear all over the place.

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Old 11th Feb 2020, 10:03 am   #4
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Default Re: Horrible distortion at times on 198KHZ Radio4

Thanks for the responses. It is always difficult to try and diagnose a problem that someone else is having, and although the ideas are of course possibilities that might be considered, they certainly are not applicable in this case.

I'm a long time Radio Amateur myself and the distortion does sound like SSB being demodulated by an AM system, but it isn't SSB nearby, or an inter-modulation product. It is absolutely synchronous with the speech on the programme, gradually morphing from perfectly intelligible speech into the distorted mess that I describe. I have a recording of it, but can't spot how to load the file up onto the site. I will need to host it somewhere on line and provide a link perhaps.

The give away is that no other nearby station is affected like this - and by the way, I have no transmissions near by. I live in a rural location and the nearest RF source is a TV repeater about four miles away with an output power of about 400 watts operating at around 800 MHZ. This operates 24/7, so sporadic fading and distortion is unlikely to come from that.

I've seen and read a long thread ending about a year ago on here about sibilence on the 198 LW signal and having looked at the expanded waterfall trace of the 198 khz spectrum it does have some anomalies. The side bands are not even, and sometimes extend beyond the 6khz bandwidth marker of the receiver. I wonder if one of the transmitters is operating out of spec.

I don't think it is my receiver. I have looked at dozens of AM signals on the broadcast bands - near and far and it is only this one which is doing this and then, only sometimes. It will work for hours at a time in an acceptable way and then do it.
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Old 11th Feb 2020, 10:45 am   #5
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Default Re: Horrible distortion at times on 198KHZ Radio4

I get the same effect from time to time on an ordinary R1155 rx. I doubt very much if it has anything at all to do with either SSB or amateur operators! I put it down either to propagation of possibly a side effect of synchronous transmission from two transmitters.
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Old 11th Feb 2020, 10:50 am   #6
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Default Re: Horrible distortion at times on 198KHZ Radio4

Attaching files to a post.
https://www.vintage-radio.net/forum/...l&titlesonly=0
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Old 11th Feb 2020, 11:32 am   #7
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Default Re: Horrible distortion at times on 198KHZ Radio4

Historically, any variation in 'mush' area (due to earlier types of crystal-referencee drives at Burghead & Westerglen with respect to the master station at Droitwich) was minimised by having check receivers 'mid-way' at Pontop Pike, the correction being done via tone-control over P.O.lines.

I'm given to understand that these days, the 198kHz synchronised stability is maintained to better than 5 in 10e14 by means of "accurately steered ... GPS-disciplined rubidium drives" at all three sites.

Hope this helps
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Old 11th Feb 2020, 12:25 pm   #8
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Default Re: Horrible distortion at times on 198KHZ Radio4

Newcastle is certainly going to be in a Droitwich/Westerglen overlap area.
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Old 11th Feb 2020, 12:42 pm   #9
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Default Re: Horrible distortion at times on 198KHZ Radio4

Agreed that this is almost certainly distortion due to overlap.

If any one transmitter is dominant then it will sound fine. If ever there is an equi signal condition between 2 of the sources while the third one is much lower in level then distortion is to be expected due to selective cancellation effects.

All the other stations mentioned that "sound fine" are single site TX I believe.

You might find turning your loop makes an improvement. (or not!!) It would be interesting to know what is the orientation of the loop relative to the 3 TX sites please.
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Old 11th Feb 2020, 12:47 pm   #10
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Default Re: Horrible distortion at times on 198KHZ Radio4

Quote:
Originally Posted by paulsherwin View Post
Newcastle is certainly going to be in a Droitwich/Westerglen overlap area.
Yes it is Paul. I've moved since i joined here and am forty miles west of Newcastle near Brampton, but 198khz is a poor signal on even a quite decent portable unless some sort of tuned passive loop is coupled to the loopsticks.

My Kiwi SDR is currently running on a big loop of about forty metres of wire, two thirds of which is literally lying on the ground and the other third is at a maximum about three feet above the ground, running along a hedge. This is a surprisingly effective, broadband antenna when linked to the coax by a 4:1 balun. It pulls in 252KHZ RTE rather well, and works down to a few khz better than many other configurations I have tried. It also works up to low HF if the bands are open. The main reason I tried the loop on the ground, was in an effort to reject my neighbour's TV / networking hash. Antennas at any height at all produced a high noise level.

On the topic focus, I am wondering if the overlap you mention combined with propagation fading might account for it. If nobody else is noticing it, it is probably something of the sort.
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Old 11th Feb 2020, 12:52 pm   #11
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Default Re: Horrible distortion at times on 198KHZ Radio4

Quote:
Originally Posted by Jon_G4MDC View Post
Agreed that this is almost certainly distortion due to overlap.

If any one transmitter is dominant then it will sound fine. If ever there is an equi signal condition between 2 of the sources while the third one is much lower in level then distortion is to be expected due to selective cancellation effects.

All the other stations mentioned that "sound fine" are single site TX I believe.

You might find turning your loop makes an improvement. (or not!!) It would be interesting to know what is the orientation of the loop relative to the 3 TX sites please.

This would be a good way forward. I have been wondering about going for a small magnetic loop antenna just for a winter project. I don't want to throw my wallet at it though, so I was considering either one of those cheap MLA30 loops, or making something myself. There are various simple designs of broadband, amplified loops. My rather huge loop on the ground ain't going to be steerable though. I don't have that sort of real estate )

I spotted someone down your way (Bedford) on my SDR log, this morning, so it might have been you. He was listening to some cw on 40. The band is pretty down at the minute so if it was you, feel free to have another go at another time when the propagation is better. Forty was crawling with strong signals on the cw section at the weekend. I have also been quite impressed by the pick up of aeronautical HF signals on 5649 khz usb. I can hear the planes pretty well along with the massive Shanwick signal which used to be the only readable signal on other antennas used in the past. Shannon Volmet is a good test signal for the state of propagation at the MF on 5505KHZ USB

Last edited by Tony1951; 11th Feb 2020 at 1:02 pm.
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Old 11th Feb 2020, 12:57 pm   #12
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Default Re: Horrible distortion at times on 198KHZ Radio4

OK Tony, you didn't mention the direction of your loop in either post. Does it run N-S or E-W or other? Given the TX power differences (10dB) you are likely in the equisignal for Westerglen and Droitwich - note the mention of Pontop Pike as a monitor station for them. It's probably Burghead sitting under both of those while they fight it out.

I would look around online for the Wellgood Loop if you fancy rolling one of your own.
There might even be something on it in past posts on here.

<Edit> Just thought of something else that could be fun. Make 2 loops and space them apart on the line between Westerglen and Droitwich. Combine them so that by phasing they add in one direction or the other. Now you can reject an unwanted one by reversing the phase.

Last edited by Jon_G4MDC; 11th Feb 2020 at 1:03 pm.
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Old 11th Feb 2020, 2:20 pm   #13
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Default Re: Horrible distortion at times on 198KHZ Radio4

Quote:
Originally Posted by Jon_G4MDC View Post
OK Tony, you didn't mention the direction of your loop in either post. Does it run N-S or E-W or other? Given the TX power differences (10dB) you are likely in the equisignal for Westerglen and Droitwich - note the mention of Pontop Pike as a monitor station for them. It's probably Burghead sitting under both of those while they fight it out.

I would look around online for the Wellgood Loop if you fancy rolling one of your own.
There might even be something on it in past posts on here.

<Edit> Just thought of something else that could be fun. Make 2 loops and space them apart on the line between Westerglen and Droitwich. Combine them so that by phasing they add in one direction or the other. Now you can reject an unwanted one by reversing the phase.
Thanks for the ideas John and sorry to be unclear about the antenna.

It is a horizontal loop 17 paces by four, running north south on the long axis. Three sides of it are lying on gravel and one side is on average about three feet above the ground on a hedge. It is made up of 26 swg enamelled wire and the balun is a home made one on a ferrite core I had lying around.

The balun consists of six turns on the loop side and two on the rx side. I pinched the design from someone online who claimed it was a 4:1 isolation balun. The whole thing is more a proof of concept test than a final antenna, but it works well enough on my lf/mf areas of interest delivering an snr of about 30-40db on my main areas of interest when the bands are open.

I came to the idea of the loop on the ground concept because I get some noise from a neighbour's systems. I only discovered who the suspect is when it went off last night at midnight so I may presently move to a mag loop to null it out.

In the past I made a PA0rdt miniwhip in ugly construction and if the Wellgood amp can realistically be made like that I could be tempted to have a go, but to be fair, this big, very very cheap loop on the ground has way surpassed what I thought it might deliver.

I had a 60 foot long wire up before, followed by a forty meter vertical loop whose top run was about 20 feet up and the lower run more or less on the ground (running north south) and although the signals were much stronger, the noise was pretty horrific and the snr was less than what I now have.

The vertical loop used to get the same occasional distortion on 198Khz too.


Nice clean signal at lunch time from Radio 4. Compare to RTL 252Khz. Note the contraction in bandwidth when a telephone caller was broadcast on the 252 frequency.
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Last edited by Tony1951; 11th Feb 2020 at 2:35 pm.
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Old 11th Feb 2020, 2:25 pm   #14
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Default Re: Horrible distortion at times on 198KHZ Radio4

Someone had morse on LW broadcast the other day on this forum.

Lawrence.
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Old 11th Feb 2020, 2:28 pm   #15
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Default Re: Horrible distortion at times on 198KHZ Radio4

Quote:
Originally Posted by Nymrod121 View Post
Historically, any variation in 'mush' area (due to earlier types of crystal-referencee drives at Burghead & Westerglen with respect to the master station at Droitwich) was minimised by having check receivers 'mid-way' at Pontop Pike, the correction being done via tone-control over P.O.lines.
This apparatus used to be at Sandale back in early 1980s - big loop antenna outside. I thought the Mush Area between Droitwich and Westerglen is why BBC R4 (LF feed) is transmitted on MF from the Brisco transmitter at Carlisle: to act as a 'filler' on 1485kHz.

Guy - sorry... Haven't been in touch yet - will give you another call (you were unavailable!)
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Old 11th Feb 2020, 2:29 pm   #16
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Default Re: Horrible distortion at times on 198KHZ Radio4

I am the guilty party in Bedford Tony! Really enjoyed tuning your SDR around. One of these days I will indulge but thanks for making yours available. I was impressed by the relatively low noise level at your location.

R4 LW was fine when I listened. As others suggest, I strongly suspect it is due to constructive/destructive effects from the three transmitters with none being dominant. I have a magnetic loop based on an amplifier by LZ1AQ. He has an excellent site with lots of theory and practice.
http://lz1aq.signacor.com/
Mine works very well and I find it especially useful to be able to switch remotely from loop to short dipole. It's amazing the difference this can sometimes make. It goes down very low in frequency too. I noticed the ebay loop you mentioned and would be interested to hear of any experiences of it.

I spent the first 18 years of life in Alnwick, even further north than you and am very envious of your location!

Ian
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Old 11th Feb 2020, 2:39 pm   #17
Tony1951
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Default Re: Horrible distortion at times on 198KHZ Radio4

Quote:
Originally Posted by russell_w_b View Post
Quote:
Originally Posted by Nymrod121 View Post
Historically, any variation in 'mush' area (due to earlier types of crystal-referencee drives at Burghead & Westerglen with respect to the master station at Droitwich) was minimised by having check receivers 'mid-way' at Pontop Pike, the correction being done via tone-control over P.O.lines.
This apparatus used to be at Sandale back in early 1980s - big loop antenna outside. I thought the Mush Area between Droitwich and Westerglen is why BBC R4 (LF feed) is transmitted on MF from the Brisco transmitter at Carlisle: to act as a 'filler' on 1485kHz.
That is right I think, and they also broadcast MW Radio 4 on Tyneside on 603KHZ at a power level of about 750 watts. It used to be a 2kW signal, but they have quietly reduced it of late. The reception was problematic at both ends of the Tyne Gap and I am about half way between them.
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Old 11th Feb 2020, 2:51 pm   #18
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Default Re: Horrible distortion at times on 198KHZ Radio4

You are very welcome to tune the thing Ian. use it any time it isn't full up. I am also decoding wspr on it on 40 meters. I think if it is full - it only has four slots, it will just return a not available message.

As for low noise level. The spectrum shown in the first ttachement was what you experienced and the second, is the much much cleaner state when my neighbour switched off something last night at midnight. Most of the noise is around 15mhz to 25 mhz which fortunately is pretty dead for propagation these days anyway.
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Old 11th Feb 2020, 2:56 pm   #19
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Default Re: Horrible distortion at times on 198KHZ Radio4

Thanks for info Tony.
I was pondering on something like a ZL special for longwave which could be a lot of fun.
That is until you work out how far apart you would need to space the 2 elements.
I don't think this idea would fly.

Maybe a loop and a vertical, as per the "sense" aerial on a DF receiver, might work out.
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