2m tvi stub
 

In message , Dave
Oldridge writes
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.

If you have no test equipment, simply cut the stub when listening to
preferably strong signals on a 2m receiver, and transfer it to the input
of you TV amplifier.

As stated in another post, a single stub is fairly broad. The notch will
be typically 25dB deep on 145MHz, but it will still cause considerable
attenuation of any TV signals around 175MHz. However, it is quick to
make, and it should tell you if you are on the right track for
eliminating the TVI. If necessary, you can improve it.

Two stubs, separated by an electrical quarterwave, are much sharper and
deeper than a single stub.

As has also been mentioned, a 145MHz stub will also remove signals on
odd harmonic frequencies (ie 435 and 725MHz). Any TV around 725MHz?
--
Ian

2m tvi stub
 

In article ,
"JB" wrote:

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.

hi

There never w as any filters just antenna going into a master am,
that had a tone of settings but i don't think anything was build
into the amp to actually filter or notch the current one is a Pico
52 it has gain tilt attenuation fm trap going from memory i
think thats it

but previously no external filters the prev master amp was
blounder tongue seemd to have simular settings

since the reception is so poor now perhaps once they fix/ballance
out the system that might also reduce some 2m interference

good idea you had

2m tvi stub radials
 

In article ,
"Dale Parfitt" wrote:

"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

thanks Mike and Dale, hmm so that is a pickle if it notches
out a TV channel hmmm that would be bad the UHF stations would
also be the most week so i guess then i would be sol

perhaps i'd have to use a commercial notch filter then

it's unsure if by coiedence if the harmonics might fall out on a
few of the unused channels or not


hmm

than again i ponder if the digital tv would simply not be
effected by the 10m or 2m rigs, then again could be worse but
perhaps digital tv might actually 'save me''

again i appreciate all those that responded i have a lot of good
ideas to experiement and try


happy new yrs

2m tvi stub
 

======= FOLLOW-UP ====== FOLLOW-UP =======

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

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.

snip

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.

I have good and bad news to add:

Last night I built some stubs with TV coax and BNC T-connectors. I swept
them with a spec-an/tracking-generator. I could produce a nice 2m notch
with one stub and (by careful trimming) a nice bandstop filter with two
stubs, separated by an intermediate length of cable. There was some ripple
in the passband, probably due to impedance discontinuities. That's the good
news.

The bad news is that there was also loss at freqs for UHF channels 14, 15 &
16, as well as Channels 45 and up. (If your building had separate antennas
for VHF and UHF, this effect could probably be avoided. You trap the VHF
antenna cable, then join the separate U/V antennas at the amp input. Maybe
the amp has provision for separate VHF & UHF antenna inputs. Many do.)

Back to good news: My junkbox contained a midband trap, a Winegard BRF-170
which I put in line and found it to be near-perfect. Stopband between 120
and 160 (about 25 dB) with minimal effect on the passband.

Bad news, http://winegard.com/offair/traps.htm doesn't show the product.
I'm still looking.

Good news: I also have a highpass filter, a Pico TTHPF02M. It attenuates
everything below 50 MHz, good for what you said might be a 10m EMI problem.
I've found recent references to it in other NGs, but no sign of a vendor for
exactly that item. News is still OK, as a "filter" search of the Picomacom
website switched me directly to a Yahoo purchase website, where they offer a
similar product http://yhst-18278607509093.stores.ya...pico-0145.html.
TV highpass filters with cutoff around 50 MHz are fairly common. For a few
bucks, try one if you confirm a 10m problem.

I hope this helps.

"Sal"
(KD6VKW)