after my building changed to a new tv antenna and master amp
seems i am giving alot of tvi on strangly enough 2m

also some tvi from 10m too never did before

my antenna is physically pretty close to the antenna (thou it also
was previsiously )

for an experiment i was thinking about just making a coaxial stub
for 2m to see if that would 'notch ' out the interference

and using a T connector putting it just before the master amp (which
i think is just amplifing my 2m signal and mixing w/the tv channels
and or overloading the tv's)


should the stub be 1/4w on 2m or would say 1/2w be 'better'?

i'd cut it for the center of 2m


tnx

ML wrote:
"----seems like I am giving a lot of TVI on strangely enough 2m."

Probably receiving amplifier overload.

Antennas usually couple more tightly side by side than they do end to
end where they reside in each other`s nulls. If the TV antenna is
horizintally polarized while your transmitting antenna is vertically
polarized. that should greatly decrease coupling between the antennas.
Maybe distance between the two antennas can be maximized. Maybe the new
TV antenna has a feedline defect allowing the line to become part of the
receiving antenna. Its coax should prevent noise pickup not cause it.
Maybe careful adjusting cross-polarization of the antennas, or a
combination of cures will fix your problem. I hope you are lucky.

Best regards, Richard Harrison, KB5WZI

Usually a 1/4 wave open stub, or a half wave shorted stub...

I used to use 1/4 wave stubs to attenuate strong local TV signals from a
masthead amp that was primarily used for weaker signals. The frequency
of the wanted vs interferring signal were a nice 2:1 relationship so I
was kind of lucky. I used 75r coax and just chopped it to about .82VF
and it actually worked first time.

I'd suspect though that the problem is more likely to be fundamental
overload. Of course it cant hurt to try.

Both a 1/4 wave open and 1/2 wave short stub present a low Z to the
tuned frequency, or if you like "shorts it out", If however the wanted
pass freqency is an odd multiple (1/4 wave) or an even multiple (1/2
wave) then you end up attentuating that as well.

Cheers Bob VK2YQA

ml wrote:
after my building changed to a new tv antenna and master amp
seems i am giving alot of tvi on strangly enough 2m

"ml" wrote in message
...
after my building changed to a new tv antenna and master amp
seems i am giving alot of tvi on strangly enough 2m

also some tvi from 10m too never did before

my antenna is physically pretty close to the antenna (thou it also
was previsiously )

for an experiment i was thinking about just making a coaxial stub
for 2m to see if that would 'notch ' out the interference

and using a T connector putting it just before the master amp (which
i think is just amplifing my 2m signal and mixing w/the tv channels
and or overloading the tv's)


should the stub be 1/4w on 2m or would say 1/2w be 'better'?

i'd cut it for the center of 2m


tnx

Open quarter wave, shorted half wave. I don't know which is better.
Remember to shorten the stub length by the velocity factor of the coax.

I had a similar problem years ago on a Navy ship. Nearby taxi radios around
154 MHz overloaded the antenna amp. I bought a "Midband Trap" from a TV
shop downtown which fixed things. It went inline and attenuated those
non-TV signals between (approx) 120 - 170 MHz. It was only a few dollars
from one of the well-known TV reception equipment makers, Channel Master, I
think.

Unfortunately, I haven't found it from any familiar names, but I did locate
this page http://www.microwavefilter.com/pdffiles/pg27.pdf. The 3367-A/I,
3367-B/G, 3367-C/G and 3367-C/H should all do what you need for 2m
suppression. Prices unknown.

.... and this page: http://www.atvresearch.com/overstk.pdf Find their
number 5KMT-A/I-TX Midband Trap. A clearance sale bargain if they still
have any left.

Here's a single-frequency tunable notch;
http://www.microwavefilter.com/pdffiles/pg28.pdf.

Good luck.

In article ,
(Richard Harrison) wrote:

ML wrote:
"----seems like I am giving a lot of TVI on strangely enough 2m."

Probably receiving amplifier overload.

Antennas usually couple more tightly side by side than they do end to
end where they reside in each other`s nulls. If the TV antenna is
horizintally polarized while your transmitting antenna is vertically
polarized. that should greatly decrease coupling between the antennas.
Maybe distance between the two antennas can be maximized. Maybe the new
TV antenna has a feedline defect allowing the line to become part of the
receiving antenna. Its coax should prevent noise pickup not cause it.
Maybe careful adjusting cross-polarization of the antennas, or a
combination of cures will fix your problem. I hope you are lucky.

Best regards, Richard Harrison, KB5WZI

big thanks to all those that replied

I agree it is prob 'overload' but thought perhaps notching might
work, i already have some really good multistage tvi filters but
wanted to be ready with a notch for when the building lets me into
the closet in case that is not enough.

My thought was to try and make stubs cause they are 'cheep' but
those links to the commercial site were pretty cool

wasn't sure the difference between the single stop unit and the one
with 2 stops (past the obvious)

my thoughts would be that either wont effect the other
frequencies as a stub might (2nd 3rd harmonic?)

Currently have 2 2m antennas Rich, once is a arrow 2/440 jpole
and it is about middle of the antenna towards it's left side
about 2 ft or so away

directly in front of it is a M2 eggbeater rather omni pattern

it's about 3-4ft away so the tv antenna is looking right at it

I don't really have any place to move the antennas to other than
some sort of compramise like moving the antenna towards the floor
wich then the elevator room would block me in at least 1 compas
direction and losing the altitude would of course loose me the
distant repeaters using one of those floor mounts which i already
have actually


question
perhaps putting the 2m antenna higher than the tvi antenna might do
the trick ? the jpole has no radials the eggbeater does so i am
guessing the eggbeater might offer less downward radation? and
therefore offer less tvi if higher than the tv ant?

thanks

"Sal M. Onella" wrote in message
...

"ml" wrote in message
...
after my building changed to a new tv antenna and master amp
seems i am giving alot of tvi on strangly enough 2m

also some tvi from 10m too never did before

my antenna is physically pretty close to the antenna (thou it also
was previsiously )

for an experiment i was thinking about just making a coaxial stub
for 2m to see if that would 'notch ' out the interference

and using a T connector putting it just before the master amp (which
i think is just amplifing my 2m signal and mixing w/the tv channels
and or overloading the tv's)


should the stub be 1/4w on 2m or would say 1/2w be 'better'?

i'd cut it for the center of 2m


tnx

Open quarter wave, shorted half wave. I don't know which is better.
Remember to shorten the stub length by the velocity factor of the coax.

I had a similar problem years ago on a Navy ship. Nearby taxi radios
around
154 MHz overloaded the antenna amp. I bought a "Midband Trap" from a TV
shop downtown which fixed things. It went inline and attenuated those
non-TV signals between (approx) 120 - 170 MHz. It was only a few dollars
from one of the well-known TV reception equipment makers, Channel Master,
I
think.

Unfortunately, I haven't found it from any familiar names, but I did
locate
this page http://www.microwavefilter.com/pdffiles/pg27.pdf. The
3367-A/I,
3367-B/G, 3367-C/G and 3367-C/H should all do what you need for 2m
suppression. Prices unknown.

... and this page: http://www.atvresearch.com/overstk.pdf Find their
number 5KMT-A/I-TX Midband Trap. A clearance sale bargain if they still
have any left.

Here's a single-frequency tunable notch;
http://www.microwavefilter.com/pdffiles/pg28.pdf.

Good luck.


Professionally its often done with a pair of stubs shunting the transmission
line with a quarter wavelength of line between their junctions so the shunt
low impedance of each appears as a high impedance where the other stub is
connected. Sometimes the Q is increased by using resonators with lower loss
than co-ax cable (e.g. cavities or helical resonators). The resonant
frequencies can be staggered a bit to improve temperature stability.

An interesting homebrew affair that can yield an impressively narrow notch
is the bridged 'T' circuit, like
http://www.hobby-electronics.info/co...l/ch20s04.html, one of which is
explained at http://www.hobby-electronics.info/co...l/ch20s04.html.
The temperature stability is only as good as the (lumped) components but
using a preset variable resistor allows the loss resistance of the coil to
be cancelled out to some extent. For 2m I have used the centre-tapped L
version but with the input and output lines tapped into the coil, which
preserves more of its Q. It worked well for 'listen through' from a 2m
repeater with 600 kHz separation, using separate Tx and Rx antennas.

Chris

154 MHz overloaded the antenna amp. I bought a "Midband Trap" from a TV
shop downtown which fixed things. It went inline and attenuated those
non-TV signals between (approx) 120 - 170 MHz. It was only a few
dollars
from one of the well-known TV reception equipment makers, Channel
Master,
I
think.

Unfortunately, I haven't found it from any familiar names, but I did
locate
this page http://www.microwavefilter.com/pdffiles/pg27.pdf. The
3367-A/I,
3367-B/G, 3367-C/G and 3367-C/H should all do what you need for 2m
suppression. Prices unknown.

... and this page: http://www.atvresearch.com/overstk.pdf Find their
number 5KMT-A/I-TX Midband Trap. A clearance sale bargain if they still
have any left.

Here's a single-frequency tunable notch;
http://www.microwavefilter.com/pdffiles/pg28.pdf.

Good luck.
These are pretty common in the CATV business where they will notch channels
to put their own access channel in place.

It is likely the CATV guy came out and took all the filters out in
preparation for the digital channel changeovers. There ought to be a High
pass filter to cuttoff below channel 2 and likely a notch for VHF
air/commercial?ham energy. They may have also goofed around with a cheap
distribution amp. Many of the good setups would split up and break out
individual channels to peak or attenuate to try to balance the lineup.

ml wrote:

I agree it is prob 'overload' but thought perhaps notching might
work, i already have some really good multistage tvi filters but
wanted to be ready with a notch for when the building lets me into
the closet in case that is not enough.

My thought was to try and make stubs cause they are 'cheep' but
those links to the commercial site were pretty cool


Stubs work very well. You should try the single wire stub first.

You'll want good low loss coax. The better, the deeper the notch.

1/4 wave for the middle of the 2 meter band, and open at the end should
take out the 2 meter overload.

Anecdotally, I used a single stub during a contest to knock out overload
from 40 meters @ over a kilowatt. The antennas were around 50 feet away
from each other.

- 73 de Mike N3LI -

"Mike Coslo" wrote in message
...
ml wrote:

I agree it is prob 'overload' but thought perhaps notching might
work, i already have some really good multistage tvi filters but
wanted to be ready with a notch for when the building lets me into
the closet in case that is not enough. My thought was to try and
make stubs cause they are 'cheep' but those links to the commercial
site were pretty cool


Stubs work very well. You should try the single wire stub first.

You'll want good low loss coax. The better, the deeper the notch.

1/4 wave for the middle of the 2 meter band, and open at the end should
take out the 2 meter overload.

Anecdotally, I used a single stub during a contest to knock out overload
from 40 meters @ over a kilowatt. The antennas were around 50 feet away
from each other.

- 73 de Mike N3LI -

Being a 2 pole circuit, the stubs are quite broad and because they appear
as a shunt capacity or inductance off frequency can cause major VSWR upset.
The other drawback which may be an issue for TV is that they will also notch
out frequencies at 2N+1 (odd multiples).

Dale W4OP

ml wrote in :

after my building changed to a new tv antenna and master amp
seems i am giving alot of tvi on strangly enough 2m

also some tvi from 10m too never did before

my antenna is physically pretty close to the antenna (thou it also
was previsiously )

for an experiment i was thinking about just making a coaxial stub
for 2m to see if that would 'notch ' out the interference

and using a T connector putting it just before the master amp (which
i think is just amplifing my 2m signal and mixing w/the tv channels
and or overloading the tv's)


should the stub be 1/4w on 2m or would say 1/2w be 'better'?

i'd cut it for the center of 2m

Try an open quarter-wave stub. Remember to take the velocity factor for
the stub line into account when you cut it. Alternately a shorted half
wave stub would be OK.



--
Dave Oldridge+
ICQ 454777283