MW: Local class D station still broadcasting at midnight

[majoco]

I made a "QRM eliminator" some time a go and it worked well getting rid of a lot of noise from what I suspected was a plasma TV. Shortly afterwards the neighbours moved and took the TV with them!
It's all documented here...

https://forums.radioreference.com/receive-antennas-below-30mhz/357863-qrm-eliminator.html

 

[RFI-EMI-GUY]

I made a "QRM eliminator" some time a go and it worked well getting rid of a lot of noise from what I suspected was a plasma TV. Shortly afterwards the neighbours moved and took the TV with them!
It's all documented here...

https://forums.radioreference.com/receive-antennas-below-30mhz/357863-qrm-eliminator.html

Nice project. I filed away for future.

Is there any signal loss once it is adjusted?

Are the pots linear or logarithmic taper?

 

[majoco]

Is there any signal loss once it is adjusted?

Exactly the opposite - in fact there might be too much gain in the FET amplifiers.

Are the pots linear or logarithmic taper?

Definitely linear.

In hindsight, this project was actually more trouble than it's worth! Works great on the LW and MW bands, it has a rejection bandwidth of about 20kHz on LW reducing to about 5kHz at the top of the MW band - I tried reducing the Q of the transformer but it didn't appear to change much. The main 'defect' is that although it's good at reducing local man-made interference and will completely tune out a station in the MW band in the day time, it just doesn't work at night on MW or HF with reflected signals from further afield. Sure, you can tune it out for a minute or so, but the phase of the reflected signal changes as the ionosphere goes up and down so you end up twiddling again.. and again... The bandwidth is very narrow on HF and so rejects perhaps only one sideband still leaving the monkey-chatter.
Interesting experiment but only 5 out of 10!

Ridgy - you might like to try tuning your receiver to the offending (offensive?) station and trying to reduce it's strength with your 'Timewave' and then tuning back to your favourite - sometimes you can't see the wood for the trees!

 

[ridgescan]

Exactly the opposite - in fact there might be too much gain in the FET amplifiers.

Definitely linear.

In hindsight, this project was actually more trouble than it's worth! Works great on the LW and MW bands, it has a rejection bandwidth of about 20kHz on LW reducing to about 5kHz at the top of the MW band - I tried reducing the Q of the transformer but it didn't appear to change much. The main 'defect' is that although it's good at reducing local man-made interference and will completely tune out a station in the MW band in the day time, it just doesn't work at night on MW or HF with reflected signals from further afield. Sure, you can tune it out for a minute or so, but the phase of the reflected signal changes as the ionosphere goes up and down so you end up twiddling again.. and again... The bandwidth is very narrow on HF and so rejects perhaps only one sideband still leaving the monkey-chatter.
Interesting experiment but only 5 out of 10!

Ridgy - you might like to try tuning your receiver to the offending (offensive?) station and trying to reduce it's strength with your 'Timewave' and then tuning back to your favourite - sometimes you can't see the wood for the trees!

I will try that at day's end Marty thanks!

 

[WA8ZTZ]

Had a chance yesterday to do some experimenting with the AN 200 loop. There are a couple of local 50 kw blowtorches that run IBOC. The small loop is incapable of completely nulling them out on the carrier frequency but the good news is that it completely nulls out the hash on the adjacent channels.

 

[a29zuk]

If you have a receiver with a narrow ssb filter, use the sideband nearest to the offending adjacent IBOC station to knock out the hash. It doesn't make sense but it works.

Jim

 

[WA8ZTZ]

If you have a receiver with a narrow ssb filter, use the sideband nearest to the offending adjacent IBOC station to knock out the hash. It doesn't make sense but it works.

Jim

Jim, are you referring to Exalted Carrier Selectable Sideband reception?... good idea.

 

[a29zuk]

Yes, ECSS...like I said it doesn't make sense, but it works. Theoretically you would think the sideband on the opposite side of the adjacent IBOC station would work better. It was more luck than a good idea. I was stepping through the modes on my Palstar R30 and found out by mistake trying to hear a station either on 940 or 960 with WWJ on 950 tearing them up.

Jim

 

[WA8ZTZ]

The Palstar has a reputation for being a hot receiver for LW/MW work. Many receivers are purposely made less sensitive below the 160 meter band ostensibly to prevent AM BCB overload. The Palstar apparently is not desensitized according to its sensitivity specs.

Anyway, it would be interesting to contact Palstar and get the technical explanation for what you observe regarding reception on the opposite sideband.

 

[a29zuk]

I don't think it is a Palstar thing. I think it would work with any receiver with ECSS. The nearer sideband just takes out the adjacent channel IBOC hash.

 

[WA8ZTZ]

I don't think it is a Palstar thing. I think it would work with any receiver with ECSS. The nearer sideband just takes out the adjacent channel IBOC hash.

You're right.

Tried it on my Alinco DX-SR8T... tuned to 960 in LSB mode and received WFIR Roanoke VA. Switching in the narrow 1 kc filter completely eliminated the hash. With the 2.4 kc filter, the audio sounded a bit more natural but at the price of introducing some noise.

Have never been able to receive anything either side of 950. Thanks for the tip