Local station bad harmonics on 80 meters
 

Why all this stuff about "high pass filters" and such. You are dealing with
a spot frequency, not a band of frequencies. A simple parallel resonant
notch filter should do the job quite nicely and still pass everything from
DC to daylight except that spot frequency.

Jim

Local station bad harmonics on 80 meters
 

"Michael Black" wrote in message
...
"R. Scott" ) writes:
80 is basically useless. 3400 and 4000 I have a Pegged meter WFM signal
from 1380kc station here. I have mini harmonics ever 200kc that
basically makes 80meters unusable Its really annoying and the station
says they had their equipment recertified 2 months ago

This is hardly an antenna issue.

I know, but I thought it might be for them or me, so I came here (one of the
only groups I subscribe to)

You do realize that it may not be the transmitter?

Possibly, but You never know, it might have to do with their plans on moving
the antenna and upping power or the
recent storms we've had.

If your receiver (and you don't specify what it is) hasn't got
good strong signal-handling, the station may be overloading it
and causing the junk. And at first glance, it wouldn't be
obvious whether it's the receiver or the transmitter.

ICOM 706MKIIG ... Never had a problem in the 2 years Ive owned it, havnt
changed anything at my end.

Try a different receiver.

Ill see what I can find to use, good idea.


Borrow a spectrum analyzer, which should stand up well to strong
signals since it wouldn't be much use otherwise, and see what signals
are arriving at your antenna. If you do see signals that are traceable
to the broadcast station, then likely they do have a problem. But if
not, it's your receiver.

Ill see if I can find one

And it may not even be the receiver. There could be something acting
as a rectifier, that is picking up the transmiter signal and generating
harmonics for your receiver to pickup. A rusty rain gutter, or
a bad connection on an antenna, obviously something nearby.

only happend in the last month or two the Big clues that make me wonder is
if it was
a pure Birdie wouldnt it still be AM rather that Wide FM ? Makes me wonder
if the TX
is FMing some how.

You have no reason to doubt the station's word, especially since
they do have the rules to follow, and likely are in a worse
position than a ham with a bad signal. You are expecting the
transmitter to blame because you can't imagine your receiver
is at fault. But until you can actually rule out the latter,
you have no real reason to blame the transmitter.

I used to work at a Station and I know the rules they have to follow, I also
know that very shoddy
work is done at a lot and just signed off. Ill continue to check my end,
but If Ive never heard the
birdies before with the same station (Save the 706MKIIG and new coax on
occasion) Ive had for 18 years here
with no problems until the recent storms and the station has multiple
birdies and its in Wide FM rather than
AM ... makes me wonder.


Scotty W7PSK

Local station bad harmonics on 80 meters
 

On Wed, 24 Jan 2007 08:49:21 -0800, "RST Engineering"
wrote:

Why all this stuff about "high pass filters" and such. You are dealing with
a spot frequency, not a band of frequencies. A simple parallel resonant
notch filter should do the job quite nicely and still pass everything from
DC to daylight except that spot frequency.

Hi Jim

There's not much more effort in completely covering a band of problems
with a band reject (high pass) filter. The original poster could
discover the NEXT broadcaster creating problems when he limited his
suppression to the first one. Who needs a chain of notch filters when
one would work as well for the entire band?

73's
Richard Clark, KB7QHC

Local station bad harmonics on 80 meters
 

On Wed, 24 Jan 2007 16:49:41 GMT, "R. Scott"
wrote:

it might have to do with ...
recent storms we've had.

Hi OM,

Corrosion is a classic distortion products source that could easily
bring the problems you see.

73's
Richard Clark, KB7QHC

Local station bad harmonics on 80 meters
 

"R. Scott" wrote in message
...
with no problems until the recent storms and the station has multiple
birdies and its in Wide FM rather than
AM ... makes me wonder.

go mobile. use a small antenna and an attenuator, maybe the one in the rig
will be enough with just a 6" antenna or something like that. if it is
indeed local to your shack it should be obvious when you get a few blocks
away, then start hunting for rectifiers. it should also be obvious if it is
from the transmitter as you drive around it. that might also find it if it
happens to be from a 3rd party, like a bad ground wire on a power pole or
something.

Also, do the test of shutting off everything at the breakers in the house...
there is an outside chance, especially with the FM symptom and extreme
width, that the AM station is getting picked up by some other device and
modulating it... it could be getting into a TV and modulating the color
burst, or a computer monitor, a old cordless phone, etc.

also check their fundamental and see if you can detect the fm on it, that
should be obvious enough also and something you could go demonstrate to the
engineer that may show him they have a problem that developed after their
certification.

Local station bad harmonics on 80 meters
 

Dave wrote:
"R. Scott" wrote in message
...
with no problems until the recent storms and the station has multiple
birdies and its in Wide FM rather than
AM ... makes me wonder.

go mobile. use a small antenna and an attenuator, maybe the one in the rig
will be enough with just a 6" antenna or something like that. if it is
indeed local to your shack it should be obvious when you get a few blocks
away, then start hunting for rectifiers. it should also be obvious if it is
from the transmitter as you drive around it. that might also find it if it
happens to be from a 3rd party, like a bad ground wire on a power pole or
something.

Also, do the test of shutting off everything at the breakers in the house...
there is an outside chance, especially with the FM symptom and extreme
width, that the AM station is getting picked up by some other device and
modulating it... it could be getting into a TV and modulating the color
burst, or a computer monitor, a old cordless phone, etc.

also check their fundamental and see if you can detect the fm on it, that
should be obvious enough also and something you could go demonstrate to the
engineer that may show him they have a problem that developed after their
certification.



Phew! That's a lot of stuff!

However, if all that fails, call Ghost Busters!

Regards,
JS

Local station bad harmonics on 80 meters
 

Because he's got a SINGLE frequency interfering with his station. To hell
with covering the entire band. A single parallel resonant network will do
something in the order of 80 dB of rejection if the L and C are at LEAST
something reasonable for Q.

Care to calculate the order of filter that will do 80 dB as a low pass
filter? And the Q of the components necessary to make the insertion loss
negligible at 160 meters?


Jim


"Richard Clark" wrote in message
...
On Wed, 24 Jan 2007 08:49:21 -0800, "RST Engineering"
wrote:

Why all this stuff about "high pass filters" and such. You are dealing
with
a spot frequency, not a band of frequencies. A simple parallel resonant
notch filter should do the job quite nicely and still pass everything from
DC to daylight except that spot frequency.

Hi Jim

There's not much more effort in completely covering a band of problems
with a band reject (high pass) filter. The original poster could
discover the NEXT broadcaster creating problems when he limited his
suppression to the first one. Who needs a chain of notch filters when
one would work as well for the entire band?

73's
Richard Clark, KB7QHC

Local station bad harmonics on 80 meters
 

RST Engineering wrote:
Because he's got a SINGLE frequency interfering with his station. To hell
with covering the entire band. A single parallel resonant network will do
something in the order of 80 dB of rejection if the L and C are at LEAST
something reasonable for Q.

Care to calculate the order of filter that will do 80 dB as a low pass
filter? And the Q of the components necessary to make the insertion loss
negligible at 160 meters?


Jim


Krist! Whatever was I thinking?

Yanno, if he even just sits back and thinks about it long enough, he
might be getting excited over his present problem for nothing!

Maybe if he just practiced a little Zen he could learn to actually enjoy it?

Many roads lead to the same destination--the high pass is but one ...

Regards,
JS

Local station bad harmonics on 80 meters
 

"RST Engineering" ) writes:
Because he's got a SINGLE frequency interfering with his station. To hell
with covering the entire band. A single parallel resonant network will do
something in the order of 80 dB of rejection if the L and C are at LEAST
something reasonable for Q.

Care to calculate the order of filter that will do 80 dB as a low pass
filter? And the Q of the components necessary to make the insertion loss
negligible at 160 meters?

At the very least, it's far easier to put in a single LC notch filter to
see what it does to the offending signal.

I was trying to think of things that could be done easily to determine
whether the problem is actually the transmitter or simply receiver overload.
One can easily assemble an LC circuit in the broadcast band with available
parts to try this out, while a high pass filter requires paying good
money for it and likely mail-ordering, or at the very least ordering
multiple coils to build up such a thing.

My first receiver was a cheap low end solid-state Hallicrafters in 1971,
and it overloaded terribly. I don't think anything could have been
done to fix it, but I know one time I took the parts list from the Handbook
for the high pass filter that was in there to solve the problem of AM
broadcast stations, and the parts store said they didn't have the
coils in stock, and they'd cost a pretty penny (certainly a pretty
penny for a 12 year old).

Michael VE2BVW

Local station bad harmonics on 80 meters