I currently have a 10KW Henry low pass filter in my transmission line to my
SteppIr.  I put it where my 7/8 Andrew hard line switches to LMR600DB at the
base of the tower.  I did it as an experiment to see if I could notice any
difference in RX noise.  If I determine that it actually works for that
purpose, I'll report back here.  The Henry 10 KW filter is about the size of
a shoe box, and it is made for outdoor mounting.  I actually have it under
my patio roof, which is immediately adjacent to my tower.  Though it is
mounted outdoors, it is not directly exposed to rain.

73


Alan R. Downing
Phoenix, AZ


-----Original Message-----
From: For blind ham radio operators [mailto:[log in to unmask]]
On Behalf Of eric oyen
Sent: Saturday, February 01, 2014 5:00 PM
To: [log in to unmask]
Subject: Re: Low Pass Filter

the funny thing is that low pass filters operate bi-directionally. If =
your radio produces harmonics that interfere above its normal operating =
range, then mix down products from sources above HF would also cause =
interference on HF. THese mix down products are often caused by =
interactions within the first stage of the IF in your radio. SO, using a =
filter eliminates a lot of that from getting to your radio (thus =
reducing or eliminating the problem).

I have an FM radio station transmitter site less than 3 miles from me =
producing several thousand watts. without the filter, I hear what sounds =
like FM modulated signals in a couple of bands. I put the filter in =
place, and those signals disappeared. THere are other sources (such as a =
wireless Access point, LAN switches and cable modems'DSL modems that =
produce signals that can show up in HF directly. Filtering these is a =
bit harder. I am having to use ferrite beads on the power leads and also =
on the LAN cables to try and minimize some of these issues. I have only =
been partially successful. I still get a lot of birdies in the 10 meter =
band (around 28.5). I am going to acquire a portable shortwave receiver =
and try to track these signals to their source and see what I can do to =
remove them.

-eric

On Feb 1, 2014, at 4:37 PM, John Miller wrote:

> I've never had a low pass filter help on receive. I haven't run one in =
a=20
> long time though.
> ----- Original Message -----=20
> From: "eric oyen" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Saturday, February 01, 2014 3:21 PM
> Subject: Re: Low Pass Filter
>=20
>=20
>> one would think so, however, there are a lot of other devices that =3D
>> produce noise that can be mixed down into the HF bands (either by =3D
>> interstage mixing or inter mod).. a low pass filter is still useful =
for =3D
>> reducing that incidental noise to acceptable levels. Also, when it =
comes =3D
>> to a phone patch, those are still useful (as cell phones don't work =
in =3D
>> all places).
>>=20
>> I read this somewhere: "don't forget what you already know".
>>=20
>> -eric
>>=20
>> On Jan 31, 2014, at 11:31 PM, Howard Kaufman wrote:
>>=20
>>> With modern radios and modern television, their is little need for a =
=3D
>> low=3D20
>>> pass filter.
>>> If you are going to use one, it should be as close to the transmit =3D=

>> output as=3D20
>>> possible.  With so few stations transmitting from channels 2 through =
=3D
>> 6, and=3D20
>>> the modern rigs having both auto tune and internal tuner features, I =
=3D
>> think=3D20
>>> the low pass filter has gone the way of the phone patch, and the=20
>>> plate=3D20=3D
>>=20
>>> modulator.
>>> =3D20
>>> =3D20
>>> ---
>>> This email is free from viruses and malware because avast! Antivirus =
=3D
>> protection is active.
>>> http://www.avast.com=20