"No Spam" wrote in message
. ..
I'm trying to come up with some ideas for multi-op field day station
isolation. Main problem will be front end desens between Voice and CW
portion of the same band. Main concern is on 20M

I'm thinking simple stub filters. Though they are wide, I would think
that there would be a few DB of isolation 100Khz away. Perhaps several in
parallel to narrow it up a bit.

Would a simple LC resonant circuit with perhaps 20-30Khz of BW work?

Any thing else I should be considering?


Thanks You!

coax stubs are too broad... use lumped filters if you need them, but its
hard to get real good isolation within a band. one proven way to help
prevent problems is proper prior planning of the layout, put the cw and ssb
stations as far apart as possible. if both are using dipoles or yagis
arrange them so they are in each others nulls when pointing in the prefered
direction. using one with horizontal antenna and the other vertical may
also help.

On Wed, 07 May 2008 21:35:21 +0000, Dave wrote:

"No Spam" wrote in message
. ..
I'm trying to come up with some ideas for multi-op field day station
isolation. Main problem will be front end desens between Voice and CW
portion of the same band. Main concern is on 20M

I'm thinking simple stub filters. Though they are wide, I would think
that there would be a few DB of isolation 100Khz away. Perhaps several
in parallel to narrow it up a bit.

Would a simple LC resonant circuit with perhaps 20-30Khz of BW work?

Any thing else I should be considering?


Thanks You!

coax stubs are too broad...

I thought so too, until I tried one. I was working 20 meters on a
tribander ans a KW, teh guy beside me was on a 40/30 meter fan dipole
running legal limit. Antennas were less than 50 feet apart. Without th
stub, I couldn't work period, with it, it knocked the 40 meter signal
completely out, FAPP.

-73 de Mike N3LI -

No Spam wrote:
I'm trying to come up with some ideas for multi-op field day station
isolation. Main problem will be front end desens between Voice and CW
portion of the same band. Main concern is on 20M

I'm thinking simple stub filters. Though they are wide, I would think
that there would be a few DB of isolation 100Khz away. Perhaps several in
parallel to narrow it up a bit.

Would a simple LC resonant circuit with perhaps 20-30Khz of BW work?

Any thing else I should be considering?


Thanks You!


Dear No Spam,

A simple resonant circuit centered on 14.05MHz with a 3dB bandwidth of
20KHz is a circuit of Q = 705 which is tough to make and even then will
not provide enough attenuation at 14.15MHz to be of much value.

I have done exactly what you want to do and you will not accomplish it
with LC filters and stubs alone. Assuming you wish to run 2 stations on
40m or 20m simultaneously and demand a minimum separation of 80KHz which
is only about a 0.5% spread (on 20m) you will need to be more creative.
Transmitter phase noise and receiver blocking dynamic range are the 2
issues and both are about the same magnitude problems. Your friends in
the solution of this problem are the allowed 1000' diameter circle for
FD, the different antenna polarizations, and the antenna patterns.
Expect to need about 60dB isolation between 2 antennas on the same band
if you are using current mid range transceivers such as the IC756PRO3
and maybe about 45 to 50dB isolation between the antennas if using
transceivers such as the K3. With less isolation you will still make
contacts but the noise floor will rise and you may hear receiver
artifacts. If you wish to discuss this further please contact me directly.

73,
Larry, W0QE

On May 7, 3:05 pm, Larry Benko wrote:
No Spam wrote:
I'm trying to come up with some ideas for multi-op field day station
isolation. Main problem will be front end desens between Voice and CW
portion of the same band. Main concern is on 20M

I'm thinking simple stub filters. Though they are wide, I would think
that there would be a few DB of isolation 100Khz away. Perhaps several in
parallel to narrow it up a bit.

Would a simple LC resonant circuit with perhaps 20-30Khz of BW work?

Any thing else I should be considering?

Thanks You!

Dear No Spam,

A simple resonant circuit centered on 14.05MHz with a 3dB bandwidth of
20KHz is a circuit of Q = 705 which is tough to make and even then will
not provide enough attenuation at 14.15MHz to be of much value.

I have done exactly what you want to do and you will not accomplish it
with LC filters and stubs alone. Assuming you wish to run 2 stations on
40m or 20m simultaneously and demand a minimum separation of 80KHz which
is only about a 0.5% spread (on 20m) you will need to be more creative.
Transmitter phase noise and receiver blocking dynamic range are the 2
issues and both are about the same magnitude problems. Your friends in
the solution of this problem are the allowed 1000' diameter circle for
FD, the different antenna polarizations, and the antenna patterns.
Expect to need about 60dB isolation between 2 antennas on the same band
if you are using current mid range transceivers such as the IC756PRO3
and maybe about 45 to 50dB isolation between the antennas if using
transceivers such as the K3. With less isolation you will still make
contacts but the noise floor will rise and you may hear receiver
artifacts. If you wish to discuss this further please contact me directly.

73,
Larry, W0QE

Of course Larry's right: any transmitter phase noise will be a
problem. Especially with the density of signals typical on FD, 3dB
loss in a receive filter won't be much of a problem most of the time,
but in a transmit filter it's another issue. 3dB passband attenuation
was about what I got in the filter design I was playing with this
morning, assuming coils with a Q around 400, which should be fairly
easy on 14MHz. That gave better than 25dB attenuation 100kHz away,
which should be a huge help. If you can get the coil Q up enough,
then the filter can be used on both transmit and receive, and you'll
get the same improvement in phase noise output performance that you
get on receive in rejecting the adjacent band. 100 watts will be
incentive to use large enough coils that the Q will indeed be pretty
high--assuming you don't do anything too stupid in the construction.
There are significant advantages at a multi-transmitter FD site in
having a receiver that tolerates strong signals well, and also in
having a transmitter that has low phase noise.

Cheers,
Tom

On Wed, 07 May 2008 16:05:47 -0600, Larry Benko wrote:

I have done exactly what you want to do and you will not accomplish it
with LC filters and stubs alone.

I would suggest that No Spam might try an experiment, making a stub as a
first try. It's simple enough that if it doesn't work, there isn't much
effort wasted.

Can't say for sure why some say a stub won't work, while the one I made
worked gangbusters, and cured the exact problem No Spam was looking at.

-73 de Mike N3LI -

Mike Coslo wrote:
I would suggest that No Spam might try an experiment, making a stub as a
first try. It's simple enough that if it doesn't work, there isn't much
effort wasted.
=====
Mike , Was that a single or treble stub (Pi shape) ?

Frank GM0CSZ / KN6WH

Highland Ham wrote:
Mike Coslo wrote:
I would suggest that No Spam might try an experiment, making a stub
as a first try. It's simple enough that if it doesn't work, there
isn't much effort wasted.
=====
Mike , Was that a single or treble stub (Pi shape) ?

It was a single stub. The situation was during a contest, so I had to
come up with something quick. I can only imagine something like a Pi
stub would have been all that much better.

- 73 de Mike N3LI -

On May 13, 11:43 am, Michael Coslo wrote:
Highland Ham wrote:
Mike Coslo wrote:
I would suggest that No Spam might try an experiment, making a stub
as a first try. It's simple enough that if it doesn't work, there
isn't much effort wasted.
=====
Mike , Was that a single or treble stub (Pi shape) ?

It was a single stub. The situation was during a contest, so I had to
come up with something quick. I can only imagine something like a Pi
stub would have been all that much better.

- 73 de Mike N3LI -

But as I understand it, Mike, it was to kill something at least 4MHz
away from 14MHz. That doesn't take a very high Q. The OP was asking
about killing something 100kHz away, at 14MHz, and that's entirely
different.

I assume yours was a 1/4 wave stub on the freq you wanted to kill,
open on the free end (or else a 1/2 wave stub, shorted on the free
end). If it was RG-213-size coax, I'd expect the Q at 14MHz to be
about 100. I can do that at 14MHz in a coil about 1/3 inch in
diameter and 1/3 inch long.

Cheers,
Tom

In article , No Spam
wrote:

I'm trying to come up with some ideas for multi-op field day station
isolation. Main problem will be front end desens between Voice and CW
portion of the same band. Main concern is on 20M

I'm thinking simple stub filters. Though they are wide, I would think
that there would be a few DB of isolation 100Khz away. Perhaps several in
parallel to narrow it up a bit.

Would a simple LC resonant circuit with perhaps 20-30Khz of BW work?

Any thing else I should be considering?


Thanks You!

I'd love to be able to find designs for single-band filters for FD use
-- this year we'll have 2 or 3 IC-7000 stations, at least one yagi, a
vertical, and an nvis.

Something like a low-pass for 80, high pass for 10, and bandpass for
40, 20, and 15, that can take 100W, including 100W for at least a few
seconds on the wrong band... That kind of thing happens after you've
been up for too many hours!

....signing 3 bravo sierra juliet victor

--
Namaste--

No Spam wrote:
I'm trying to come up with some ideas for multi-op field day station
isolation. Main problem will be front end desens between Voice and CW
portion of the same band. Main concern is on 20M

I'm thinking simple stub filters. Though they are wide, I would think
that there would be a few DB of isolation 100Khz away. Perhaps several in
parallel to narrow it up a bit.

Would a simple LC resonant circuit with perhaps 20-30Khz of BW work?

Any thing else I should be considering?


Thanks You!

I considered stubs and lumped-element filters but last year with the Machias
Radio Group, we ran two stations w/o any filters... an FT1000MP on CW and
TS430 on fone (http://www.geocities.com/bswadener/fd2007/). The tents were
separated by about 1000'. We had almost nonexistent issues with
interference.

If you want to work through design of lumped-element filters, Jim Tonne
WB6BLD (http://tonnesoftware.com/) has some nifty software available. Stubs
are covered in a book written by George Cutsogeorge W2VJN, "Managing
Interstation Interference - Coaxial Stubs and Filters", available he
http://www.qth.com/inrad/book.htm.

73 es gl,
Bryan WA7PRC