Splatter from local AM station
 

A local AM radio station in the Puget Sound Area,Washington State,US has
a lot of splatter to shortwave bands expecially around 5 MHZ. I by
happen to live nearby approx one mile so its quite bad. I used
to live 10 miles away and problem still persisted. I was wondering
if a 'loop' antenna such as one by Welbrook Communications could
be used to 'null' it out ? If not anyone else have any suggestions?

Bob Meader wrote:

A local AM radio station in the Puget Sound Area,Washington State,US has
a lot of splatter to shortwave bands expecially around 5 MHZ. I by
happen to live nearby approx one mile so its quite bad. I used
to live 10 miles away and problem still persisted. I was wondering
if a 'loop' antenna such as one by Welbrook Communications could
be used to 'null' it out ? If not anyone else have any suggestions?

The Wellbrook loops work fine for taking out local noise directionally.

Another alternative is an ANC-4 and a second antenna of any kind to
phase against the first; this can be used to take out all sorts of
things.

A third (if it's your receiver that's doing the splattering) is
a trap to take out the AM station's frequency in the antenna feed;
that will suppress the AM band as well in the vicinity though. But
it's very cheap.
--
Ron Hardin


On the internet, nobody knows you're a jerk.

If you've only got one station giving you trouble, try some BCB filters or even
a homebrew 'band stop' filter set just for the local station.

jw
wb9uai

You speak of "splatter" from a local Am station, particularly around 5 MHz, from
a nearby location.

To be pedantic and precise, AM splatter consists of sidebands of audio
modulation that interfere with adjacent signals. No AM radio station can
splatter out of the broadcast band to 5 MHz; it's a physical impossibility.
Even an old messy RCA Ampliphase transmitter, badly misadjusted, would not
usually splatter more than a few tens of kHz either side of carrier frequency.
So therefore you would surely mean that you are getting a *spurious signal* that
is somehow related to the station's transmission, presumably a harmonic or spur.


If it's a broadcast station harmonic being *truly* transmitted and *accurately*
received, up at 5 MHz, it would be somewhat unusual. As a broadcast engineer my
experience is that above the weak third harmonic of the carrier signal there is
rarely much being transmitted; if so, the power levels would be exceptionally
low (maybe tiny fractions of a watt at the fifth or sixth harmonic, at worst.) A
significant signal could be transmitted if the station had a real problem: such
as a spurious transmitter oscillation that somehow got 'passed' by their antenna
system (which, by definition, is well off resonance this far from the carrier
frequency, and therefore incredibly inefficient "out there" at 5 MHz...) Or
there could be a bad component in a matching network; even a re-radiation of the
signal from a corroded fence or roof fairly near the transmitter site. And two
close-by radio transmitters can interfere with each other and produce sum-and-
difference "intermod" frequencies.

But my guess is that you probably are experiencing crossmodulation effects in an
overloaded radio front-end. If so, unless you significantly attenuate the main
fundamental carrier frequency signal of the station, you aren't going to
eliminate the noise. A loop antenna surely can help, if you can orient it to
null out the local station. But you might want to try some experimentation
before spending a lot on the Wellbrook you suggest. De-couple your antenna
connection using a variable resistor or by trying a series of different values
of capacitors in the range of a few tens to hundreds of picofarads -- or even a
"gimmick" capacitor: merely break the connection of the wire leading from the
antenna to the radio antenna terminal and twist a few turns of the (insulted)
broken ends around each other, varying the number of turns and therefore the
coupling. If at some point you can reduce the signal this way so that the 5 MHz
interference goes away, you have confirmed that the radio front-end is
overloading.

You should probably also use a shielded coax line and a matching transformer,
with the coax grounded at both the radio and the transformer ends: thus the lead-
in will not itself act as an antenna for the strong local transmitter signal.

If the station is REALLY transmitting a spur up at 5 MHz (or if there is a
*real* signal being propagated in space due to this station 'interacting' with a
fence or another carrier, producing an intermodulation product), then by using a
bandpass filter to reduce the antenna gain only at broadcast band frequencies
you may not solve the problem: the 5 MHz spur (or whatever it is) won't be
affected. But if the spurious signal is YOUR radio overloading and
crossmodulating, the BC band filter (SW band highpass filter) will help, or even
completely fix the problem.

I have this trouble with my hypersensitive solid state communications receiver
and use a simple series shunt filter tuned to a local 50kW station's frequency,
right across the antenna-to-ground terminals of my radio. The filter is a
variable cap in series with a (metal-shielded) ferrite antenna coil, parts I
took from a throw-away broken transistor radio. I tune the variable cap to the
station's frequency: this filter then shunts most of that frequency to ground
(having a measurable effect of reducing the signal by 27 dB, quite a lot!) The
"one pole" filter is broad, and has a discernible effect through most of the BC
band; but well above 2 MHz in the SW bands it has no attenuation. Therefore, I
leave it in all the time, since I don't listen below the 90M band with this
radio. This simple filter, which took five minutes to make and adjust, enabled
me to cut out most of the crossmodulation effects from several local AM stations
that caused a number of discrete intermod products that peppered the tropical
band and the 80M ham band. It is interesting to note, however, that I *still*
receive some very faint second and third harmonics of two stations, "real ones"
being transmitted but within legal FCC attenuation specs: just milliwatts of
signal that my radio easily detects, close to the transmitters.

My tube-type radio picked up less of these signals, but did get SOME of them.
In the case of both radios, reducing antenna coupling did not suddenly cause
them to disappear: because the signals were really there, not merely caused by
front end overload. The tube radio heard less of them, because it is far less
sensitive than the solid-state modern receiver.

However, cheap portable SW radios and even my fairly costly Sony 7600 pick up
not only front-end crossmod products but also "wipe outs" of large portions of
the SW bands when a local SSB'er starts his rag-chews. I have tried almost
everything: filters, extra grounds, reducing antenna coupling; and nothing
really works to make the cheap radios clean and free from strong interference.
I just wait and use them at night when all the BC stations drop their power, and
when the ham is transmitting...I turn them off.

AUTEUR



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Note to original poster, Bob Meader:

Apologies for mistyping "insulated" as "insulted". No need to yell nasty things
at the wire!

AUTEUR

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Auteur wrote:
I just wait and use them at night when all the BC stations drop their power, and
when the ham is transmitting...I turn them off.

That's where a Wellbrook loop would work; or, if the ham stays on the same frequency,
a pair of antennas and an ANC-4.
--
Ron Hardin


On the internet, nobody knows you're a jerk.

BM,

Here is a Reading List, a KIT and a few prodiuts that may help you
with your BCB Interference Problems in the "HF" Shortwave Bands.

Filter, Attenuator, Preamplifier, Preselector or Barefoot
- - - by Joseph J. Carr
http://www.dxing.com/tnotes/tnote07.pdf

Dealing With AM Broadcast Band Interference Your Receiver
- - - by Joseph J. Carr
http://www.dxing.com/tnotes/tnote06.pdf

HF (SW Bands) High Pass Filters
http://www.electronics-tutorials.com...ss-filters.htm
http://my.integritynet.com.au/purdic...ss-filters.htm
"A high pass filter is simply the transformation of a low pass filter.
Just as one high pass filter design example, we will say we need a
five pole butterworth filter with a cut off frequency Fc at 2000 Khz.
That is we want to pass all frequencies above 2000 Khz but attenuate
those below 2000 Khz, that is the function of a high pass filter."

Basic Introduction to Filters: application notes on active, passive
and switched capacitor filters.
http://www.national.com/an/AN/AN-779.pdf

Chebyshev 5-element High-Pass BCB Interference Filter Kit
http://www.qrpp-i.com/kit_high-pass-filter.htm

Par BCST-HPF is designed to help shortwave listeners cope with
interference from stations under 1700 kHz
http://www.universal-radio.com/catal...ters/4426.html

BCB Interference Filters
http://www.arraysolutions.com/Produc...ersrf.html#bcb

Broadcast Band Rejection Filter by Kiwa Electronics
Coax Cable= http://www.kiwa.com/bcb.html
Random Wire Antenna= http://www.kiwa.com/bcblw.html

Noise Phasing and MFJ-1025/1026 Data
- - - by W8JI
http://www.w8ji.com/mfj-1025_1026.htm


iane ~ RHF
..
..
= = = "Bob Meader"
= = = wrote in message ...

A local AM radio station in the Puget Sound Area,
Washington State,US has a lot of splatter to shortwave bands
expecially around 5 MHZ. I by happen to live nearby approx one
mile so its quite bad. I used to live 10 miles away and problem
still persisted. I was wondering if a 'loop' antenna such as
one by Welbrook Communications could be used to 'null' it out ?
If not anyone else have any suggestions ?


..

"Auteur" wrote in message
...

You speak of "splatter" from a local Am station, particularly around 5
MHz, from
a nearby location.


I probably used the wrong term here.

If it's a broadcast station harmonic being *truly* transmitted and
*accurately*
received, up at 5 MHz, it would be somewhat unusual. As a broadcast
engineer my
experience is that above the weak third harmonic of the carrier signal
there is
rarely much being transmitted; if so, the power levels would be
exceptionally
low (maybe tiny fractions of a watt at the fifth or sixth harmonic, at
worst.)

I do get the station at exactly three times,but I also receive the
station at other spots not harmonically related.

But my guess is that you probably are experiencing crossmodulation effects
in an
overloaded radio front-end.
The odd thing is I used to live 15 miles from the station and
would receive the station on a old tube communication receiver (Collins)
with only a five foot antenna!

If it is normal to get cross modulation only 15 miles from a AM radio
transmitter, that would imply nobody near a major urban area (Chicago,
Los Angelos,New York,etc) could use a shortwave radio below
7 MHZ. Is that true?

You should probably also use a shielded coax line and a matching
transformer,
with the coax grounded at both the radio and the transformer ends: thus
the lead-
in will not itself act as an antenna for the strong local transmitter
signal.

When I moved to my new location which is approx one mile
from station I do use a shielded coax line and matching transformer. I also
purchased a new receiver a JRC nrd545. I have the problem
with both receivers. The JRC has a switchable RF antenuator of
20 db.

If the station is REALLY transmitting a spur up at 5 MHz (or if there is a
*real* signal being propagated in space due to this station 'interacting'
with a
fence or another carrier, producing an intermodulation product), then by
using a
bandpass filter to reduce the antenna gain only at broadcast band
frequencies
you may not solve the problem: the 5 MHz spur (or whatever it is) won't be
affected. But if the spurious signal is YOUR radio overloading and
crossmodulating, the BC band filter (SW band highpass filter) will help,
or even
completely fix the problem.

I have this trouble with my hypersensitive solid state communications
receiver
and use a simple series shunt filter tuned to a local 50kW station's
frequency,
right across the antenna-to-ground terminals of my radio.

I could try this.

My tube-type radio picked up less of these signals, but did get SOME of
them.
In the case of both radios, reducing antenna coupling did not suddenly
cause
them to disappear: because the signals were really there, not merely
caused by
front end overload. The tube radio heard less of them, because it is far
less
sensitive than the solid-state modern receiver.


AUTEUR



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..."splatter" from a local Am station, particularly around 5
MHz, from a nearby location.

I probably used the wrong term here.

Well, maybe, and maybe not.

As I said,
If it's a broadcast station harmonic being *truly* transmitted
and *accurately* received, up at 5 MHz, it would be somewhat
unusual.

That's been my experience in a quarter-century working around AM transmitters in
the United States, but as soon as I posted it, I read Glenn Hauser's latest DXLD,
in which he remarked that he'd picked up the TENTH harmonic of a Mexican MW
station up in the SW band! Glenn's no fool, and I'd trust his observation; the
answer is that, possibly, the standard of maintenance at that station is
abysmally poor, and the signal being radiated is SO terrible and full of illegal
garbage that this situation -- possible in that country with lax regulations,
unlikely here in the US -- could happen under some strange conditions.

Problem is that as a listener, *you don't know* at this point, since even
expensive communications receivers aren't calibrated like FCC type-accepted
field strength meters, used to measure antenna system performance. The radio
station would likely have one, if it's directional (or would need to borrow one
from time to time), and could quickly verify if there is a REAL spur out at 5
MHz, coming from their transmitter. Before I'd complain to them, though, I'd
test the problem on at least a small number of radios, and with varying antenna
lengths and couplings.

I do get the station at exactly three times,
but I also receive the station at other spots
not harmonically related.

Sounds like the *same* problem I have, four miles from a 50kW station, five or
six miles from some 5kW and 1kW stations: which is why I used a SW highpass
filter that attenuates below 2 MHz, and a notch filter for the 50kW station's
frequency. When these stations drop their power at night and either change from
ND (non-directional), to D (directional) with patterns not necessarily aiming at
ME, I can turn one or both of these filters off...but still hear some *very*
weak 2nd and 3rd harmonics: legal "wisps" of signals.

The odd thing is I used to live 15 miles from the station and
would receive the station on [an] old tube communication receiver
Collins) with only a five foot antenna!

Depending on the station's pattern, if D, and your position within a lobe or
null, this seems normal to me. In the thirties, before compact loop antennas
became commonplace, *local* station radio reception was often obtained with just
a small piece of hookup wire, even as short as you describe. A tube radio can
be made to be extremely sensitive: a Collins isn't exactly chopped chicken
liver!

Unless the station is abysmally weak -- and if it were, it wouldn't be causing
you problems! -- I'll bet an unamplified crystal set at your location (or five
miles away) could pick up the station just fine, with 5 feet of wire as an
antenna.

If it is normal to get cross modulation only 15 miles from [an]
AM radio transmitter, that would imply nobody near a major
urban area (Chicago, Los Angelos,New York, etc) could use
a shortwave radio below 7 MHZ. Is that true?

If you have a radio that is prone to internally-generated cross modulation
effects, then this is true. If you have too much signal from your antenna,
making almost ANY radio overload in one of its RF or IF stages, this could be
true. If you take pains to get a well-designed radio, and to use an antenna
that provides signals you WANT to receive, but not too much out-of-band RF that
you DO NOT want to receive, then you won't have the problem -- IF the cross mod
otherwise is generated in the radio, using a completely broadband antenna!

If the spurious signals are caused by intermods that happen when two or more
transmitting facilities are close together, with complex interactions in their
antenna systems, matching networks, and output stages (*particularly* if one or
more of the rigs is a solid-state transmitter!) you may have all kinds of
spurious signals flying around; your poor old radio will just faithfully pick
them up!

There happens to be a notorious AM radio transmission site in a certain specific
city where I used to work, where four stations intermodulate with each other.
The FCC and all other parties involved know about it, but the problems are
practically insoluble without separating all the rigs and towers; filters
installed have not helped too much. A few miles away, the junk is too faint to
detect; but as you drive by, the AM band becomes a hideous mess (SW bands too.)
Unfortunately, this antenna farm is right by the ingress/egress to a major
commuting bridge, and at the nexus of a gigantic highway complex: so tens of
thousands of people drive through the area each day. I guess they get used to
expecting their AM radios to 'crash and burn' for a mile or two; the fellows who
are MOST upset about it seem to be the managers and PD's of the stations!

When I moved to my new location which is approx one mile
from station...

Hoo-boy, do you have a problem! At a mile away, I'd scarcely expect *any* radio
to behave perfectly. So that other respondents may check, could you please post
the station's call letters and frequency? I am sure that readers in your area
may be able to scan the dial and see what their results are. What is the power
of the station, if you know? And its mode of operation: ND or D? If D, are you
in a main signal lobe? This may be determined by checking one of the websites
that give American BC station stats, based on your location. Try:
http://www.radio-locator.com/

I also purchased a new receiver a JRC nrd545. I have the problem
with both receivers. The JRC has a switchable RF antenuator of
20 db.

Good radio; but it's solid-state. Is the RF attenuator designed like many other
similar circuits: just a switchable gain function in a front-end stage, or a
voltage-controlled attenuator, using solid-state junctions? If so, even a 20 dB
attenuation may NOT eliminate internal cross-modulation in a solid state front-
end device. Older transistor radios were murder, with their sensitive and fussy
bipolar transistors. Newer ones with FETs are still difficult to design with
the same signal-handling dynamic range as boat-anchor tube radios. (And it
should be pointed out that ANY solid state device can act like a "mixer" if the
signal input is beyond the linear power-handling range.)

I myself put off buying a new solid state receiver for years due to my own
location, holding on to some tube equipment after reading all the complaints on
such forums as r.r.s. about cross-mod and overload problems. I was pleasantly
surprised that my Icom R75 could be so easily "tamed" with a tiny handful of
parts and a few minutes of work; and my antennas are 175 feet and 350 feet long,
yet in a metropolitan area bristling with AM stations. So, I have no doubt that
a JRC can be made to work reliably with the proper attention to the input. A
passive preselector, such as the well-regarded MFJ unit, could help; or you
could do as I did, and do some experimentation with antenna coupling, highpass,
and notch filters.

Happy with the results obtained with my Icom and the filters, I then tried out a
new Sony 7600; but no matter what I've done, it's a washout when a local HAM
transmits in either the 80 or 40M bands. I *think* I know who he is, and can
see a sloper and some other antennas at a house a block or two from me; I have
absolutely no reason to suspect that he isn't operating legally, so the problem
is really up to me. If you buy a cheap ($500) radio in a plastic case, expect
trouble from such nearby carriers. The Icom, however, has a metal case and good
shielding, so a combination of proper grounding, good antenna coupling, and
filtering makes it work well. I *could* build a grounded cubic Faraday shield,
insert the Sony radio into it, and run all leads to/fro via appropriate
bypassing devices. But how could I tune the radio? (The mind boggles at such a
Rube Goldberg solution.) So I play it when the HAM is not on the air...

I wouldn't burden the poor radio operator to solve this problem; he simply
couldn't. (This is one reason why *I* am not a HAM operator; as an avid
audiophile myself, I have sympathy for neighbors who might enjoy -- say -- audio
recording. Why ruin their hobby, just to blabber on about yours?)

But, remembering the inverse-square law, I am at least four to five miles away
from one of the main problematical stations that can overload my rig; you are
only ONE mile away. You may be getting a pretty hefty dose of RF at this short
distance. (If you were a bit closer, you might see if your electric toaster can
play the station!)

To summarize:

1. Obtain information about the allegedly-offending station: power, location,
antenna mode (ND or D) and if D, the pattern and where YOU are in its footprint;

2. Test your radio(s) by altering the antenna coupling and reducing the input
WELL OUTSIDE of the radio's rear antenna terminal; do not merely rely on using
the *internal* RF attenuator, which may NOT be effective against preventing
input stage crossmod tendencies.

3. Compare your reception problem with other locations, perhaps using a portable
radio. Tune in your "5 MHz splatter" signal with a portable, and drive or walk
around, and go closer and farther from the station. See what happens.

4. If you have any hint that the signals are spurious ones that MAY change
significantly if you alter the antenna coupling, then try a notch filter to
reduce the fundamental transmitting frequency of the station. This might hugely
reduce the input crossmod and clear everything up; but if junk still remains,
outside the filter's bandstop frequency range, you COULD be picking up *real*
signals being transmitted as spurs, or through re-radiation from metal surfaces
near the transmitter. Either way, the station should know about this; they must
fix the former problem, and possibly might be able to solve the latter one if
they care about their "RF community", even if the trouble is being caused, say,
by a bad gutter, a powerline, or a corroded fence well off their property.

AUTEUR (MW station broadcast engineer by profession up to the '90's.)


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"Bob Meader" wrote ...
A local AM radio station in the Puget Sound Area,Washington State,US has
a lot of splatter to shortwave bands expecially around 5 MHZ.

Been there done that. I lived a mile or so downwind of 1090-KAAY's
array in North Little Rock. They came in from 1090 to almost 8 mHz.
I was using Drakes (R-7 and R-8a) with a 240 ft random wire at 50 ft
high.

Added an antenna tuner (MJF-969) .. problem solved.

To summarize:

1. Obtain information about the allegedly-offending station: power,
location,
antenna mode (ND or D) and if D, the pattern and where YOU are in its
footprint;

The offending station is KARR ( 1460).

I have a friend living in next county north (appox 20 miles) of me has same
problem
on a 1940's Scott Receiver. I used to live 15 miles north-west of the
station and
now live 1 mile south of station.

In a later post, Bob provided information about the station in question:

To summarize:

1. Obtain information about the allegedly-offending station: power, location,
antenna mode (ND or D) and if D, the pattern and where YOU are in its
footprint;

The offending station is KARR ( 1460).

I have a friend living in next county north (appox 20 miles) of me
has same problem on a 1940's Scott Receiver. I used to live
15 miles north-west of the station and now live 1 mile south of station.

By "same problem", I take it that he too gets a splattery signal at about 5 Mhz,
that you can relate to KARR's programming by its general resemblance. It comes
in on a tube radio, and various solid-state ones; it is heard from 1 mile, to 20
miles from the station. Is this a good summation?

This would suggest that there *may* be a spur from the transmitter of KARR *if*
your observations are all well-controlled.

It is not a third or fourth harmonic: they'd fall at 4380, and 5840, well away
from 5 MHz. It could be a spur, somehow related to an internal transmitter
oscillator frequency if there is frequency multiplication involved; but since
the division of the interference signal (5 MHz) by the KARR carrier frequency is
an odd value (3.42) that does not seem at all likely to me. What may be
happening is a randomly-oscillating transmitter stage -- maybe with bad
neutralization -- whose spurious radiation is somehow passed into the antenna,
and radiated. But an AM broadcast station antenna is a highly resonant device;
way up at 5 MHz it will be quite inefficient. And there are other constraints:
the impedance of matching networks, or the complexities of phaser components,
reducing the likelihood that a really strong signal can be radiated this far
from the cx frequency. BUT IT *CAN* HAPPEN!

Perhaps, as I've suggested, if the signal is REALLY being propagated into space,
over a wide area, AND IF IT GOES AWAY WHEN KARR IS OFF THE AIR (!), then you'd
have to start looking at the possibilities that (a) the station is in terrible
shape; you should inform them!; (b) it's a strange cross-mod problem with
another station; (c) it's caused by a re-radiation effect in the near-field of
the KARR antenna system, at a hot spot where the signal is strong, and is
causing corroded metal surfaces to act as an RF mixer and passive radiator.

Once again, if the problem at 5 MHz is NOT eliminated by notching out the KARR
signal at 1460 at your antenna input (by a simple two-component series LC
filter), then (after exhausting all possibilities that you could be in error)
you probably should inquire from KARR's management and engineer if they are
interested in the phenomenon, and if they can assure you that THEY aren't
responsible for it.

I say "after exhausting all possibilities that you could be in error" with no
disrespect; I'd do the same myself before I'd contact the broadcaster.

AUTEUR

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