Re: Topband: AM broadcast multiplexing

[Jim Brown]

On 4/22/2023 10:02 AM, Rob Atkinson wrote:

I am always amazed at the hams who will buy a home within sight of a
broadcast tower.


Or this church, on a lot that borders a 50KW rig on 1160 kHz. I used 
this photo in a talk about RFI in church sound systems. At the time, 
many microphones and the most popular mic mixers had bad Pin One 
Problems, and the most widely used cables for rack wiring and mic snakes 
were of a type that convert shield current to a signal on the balanced 
pair.


k9yc.com/WJJD-Church.png

I can post a link to a talk I did for the Chicago AES Section in 2004 if 
anyone is interested. It discusses the mechanisms in detail.


73 Jim K9YC
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Re: Topband: AM broadcast multiplexing

[Rob Atkinson]

I am always amazed at the hams who will buy a home within sight of a
broadcast tower.  Rule no. 1 when looking for a new QTH is to find
where all the AM and FM plants are and avoid them; especially QRO AMs
vis a vis 160 and HF.  I remember looking around the 670 site in
Glendale Heights IL around 10 or 15 years ago, just to get a look at
the tower, guying, base pier and insulator and so on.  This is a 190
degree stick so we're talking around 800 and something feet tall.
Then I caught sight of a short free standing tower behind a house with
what appeared to be a TA33 on it, maybe half a mile away.  I know that
ham tower was not there before the 670 site was built.  I just shook
my head in bogglement.  Not sure if that's a real word or not but you
know what I mean.  Maybe he got a really good deal or his XYL insisted
on it.

73
Rob
K5UJ
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Re: Topband: AM broadcast multiplexing

[Henry Pfizenmayer via Topband]

Some years ago I had a severe AM  BC imd problem  -first thing I found was I 
needed a conductor tying the top and bottom of my T2X rotor together.(Hint was 
- I noted one night as I cycled the brake the imod would change  or go away)  



But it still existed ,not as bad, but there -I found the next source just 
probing around the yard with a IC R10 rx and its little rubber duck ant -the 
other source was a rusty turnbuckle eye bolt to another eye bolt and even 
though there was  safety wiring around the turnbuckle apparently was not  
enough to kill it or was making lousy contact .


Hank K7HP
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Re: Topband: AM broadcast multiplexing

[Frank W3LPL]

Phil,

You can use a simple direction finding antenna to locate the source
of the spurious signals

See March 2021 QST

It works very, very well

73
Frank
W3LPL



- Original Message -
From: "Phil Lefever via Topband" 
Cc: "Topband" 
Sent: Friday, April 21, 2023 5:59:50 PM
Subject: Re: Topband: AM broadcast multiplexing

Eric,

I mentioned in my post that I have a filter inline. I have tried a number of 
different configurations, different receivers, filters and attenuators. I can 
see the signals on my spectrum analyzer with the BCB filter and a healthy 
amount of attenuation also.

The spurs exist at my antenna(s). Of course there is question as to where they 
are created, at the radio transmitter site, or my neighbors chain link fence...

Was simply sharing another instance of AM multiplexing that has caused issues.

73

Phil, KB0NES


On Friday, April 21, 2023 at 11:56:25 AM CDT, Eric Scace K3NA  
wrote: 


Being so close to the transmitter site. it's quite possible that you are 
experiencing receiver front end overload, and your receiver is generating some 
of these signals.

You might wish to try the AM “brickwall” filter. DX Engineering sells them for 
$195. I have used one in many measurement situations at locations even closer 
than yours — it’s quite effective in knocking down AM broadcast signals to a 
level that eliminates receiver overload and internal IMD product generation.

— Eric K3NA
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Re: Topband: AM broadcast multiplexing

[Phil Lefever via Topband]

Eric,

I mentioned in my post that I have a filter inline. I have tried a number of 
different configurations, different receivers, filters and attenuators. I can 
see the signals on my spectrum analyzer with the BCB filter and a healthy 
amount of attenuation also.

The spurs exist at my antenna(s). Of course there is question as to where they 
are created, at the radio transmitter site, or my neighbors chain link fence...

Was simply sharing another instance of AM multiplexing that has caused issues.

73

Phil, KB0NES


On Friday, April 21, 2023 at 11:56:25 AM CDT, Eric Scace K3NA  
wrote: 


Being so close to the transmitter site. it's quite possible that you are 
experiencing receiver front end overload, and your receiver is generating some 
of these signals.

You might wish to try the AM “brickwall” filter. DX Engineering sells them for 
$195. I have used one in many measurement situations at locations even closer 
than yours — it’s quite effective in knocking down AM broadcast signals to a 
level that eliminates receiver overload and internal IMD product generation.

— Eric K3NA
_
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector

Re: Topband: AM broadcast multiplexing

[Mike Waters]

Just attenuate the signals. A few resistors is way cheaper than 195 bucks.

Or a 2k pot. ;-)

73 Mike
W0BTU

On Fri, Apr 21, 2023, 11:56 AM Eric Scace K3NA  wrote:

> Being so close to the transmitter site. it's quite possible that you are
> experiencing receiver front end overload, and your receiver is generating
> some of these signals.
>
> You might wish to try the AM “brickwall” filter <
> https://www.qsl.net/wb5wpa/Filter/AM%20Brick-Wall%20160%20Meter%20Filter.pdf>.
> DX Engineering sells them for $195 <
> https://www.dxengineering.com/parts/dlw-fl1718>. I have used one in many
> measurement situations at locations even closer than yours — it’s quite
> effective in knocking down AM broadcast signals to a level that eliminates
> receiver overload and internal IMD product generation.
>
> — Eric K3NA
>
> > On Apr 21, 2023, at 10:16, Phil Lefever via Topband <
> topband@contesting.com> wrote:
> >
> > Eric,
> >
> > I live about 3/4 mile from the multiplexed stations KKMS/WWTC (980 &
> 1280) here in MN and they are all over the ham bands in my receivers.
>
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Re: Topband: AM broadcast multiplexing

[Eric Scace K3NA]

Being so close to the transmitter site. it's quite possible that you are 
experiencing receiver front end overload, and your receiver is generating some 
of these signals.

You might wish to try the AM “brickwall” filter 
. 
DX Engineering sells them for $195 
. I have used one in many 
measurement situations at locations even closer than yours — it’s quite 
effective in knocking down AM broadcast signals to a level that eliminates 
receiver overload and internal IMD product generation.

— Eric K3NA

> On Apr 21, 2023, at 10:16, Phil Lefever via Topband  
> wrote:
> 
> Eric,
> 
> I live about 3/4 mile from the multiplexed stations KKMS/WWTC (980 & 1280) 
> here in MN and they are all over the ham bands in my receivers.
> 
> https://www.radioworld.com/tech-and-gear/tech-tips/wwtc-moves-in-with-kkms
> 
> Luckily it isn't such a problem on 160m, just the 2nd harmonic of 980 at 1960 
> is the only real issue and I seldom operate high in the band. I do have a 
> Morgan systems AM bcb filter in place.
> 
> The real issue I have is at 3540 where the 2nd harmonic of 1280 mixed with 
> 980 to give me a healthy S9+20 signal with intelligible modulation. Pity this 
> is in the heart of 80m allocation.
> 
> I have had contact with Mark Persons and the station engineer. They even 
> measured interference levels in my driveway and alas they are within specs. 
> Shame that I am just too close. I feel bad for one other ham that is about 
> 150 feet from the ends of that stations radial field!!
> 
> Kind of hoping for the demise of AM broadcasting...
> 
> 73
> 
> Phil, KB0NES
> 
> 
> 
> 
> 
> 
> On Wednesday, April 19, 2023 at 10:03:26 PM CDT, Eric Scace K3NA 
>  wrote: 
> 
> 
> 
> 
> 
> I found the 4-station site: Tri-County in Sauk Rapids MN: 7 towers, 4 
> stations, all with different day/night patterns. A report is here 
>  
> with photos.
> _
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Re: Topband: AM broadcast multiplexing

[Phil Lefever via Topband]

Eric,

I live about 3/4 mile from the multiplexed stations KKMS/WWTC (980 & 1280) here 
in MN and they are all over the ham bands in my receivers.

https://www.radioworld.com/tech-and-gear/tech-tips/wwtc-moves-in-with-kkms

Luckily it isn't such a problem on 160m, just the 2nd harmonic of 980 at 1960 
is the only real issue and I seldom operate high in the band. I do have a 
Morgan systems AM bcb filter in place.

The real issue I have is at 3540 where the 2nd harmonic of 1280 mixed with 980 
to give me a healthy S9+20 signal with intelligible modulation. Pity this is in 
the heart of 80m allocation.

I have had contact with Mark Persons and the station engineer. They even 
measured interference levels in my driveway and alas they are within specs. 
Shame that I am just too close. I feel bad for one other ham that is about 150 
feet from the ends of that stations radial field!!

Kind of hoping for the demise of AM broadcasting...

73

Phil, KB0NES






On Wednesday, April 19, 2023 at 10:03:26 PM CDT, Eric Scace K3NA 
 wrote: 





I found the 4-station site: Tri-County in Sauk Rapids MN: 7 towers, 4 stations, 
all with different day/night patterns. A report is here 
 
with photos.
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