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GM0CSZ > TECH 23.08.05 14:59l 56 Lines 2120 Bytes #999 (0) @ WW
BID : 3E2063GM0CSZ
Read: GUEST OE7FMI
Subj: Re: VHF/UHF TVI Filter
Path: DB0FHN<DB0RGB<OK0PPL<DB0RES<ON0AR<GB7FCR<GB7SAN<GB7INV<GB7NOS
Sent: 050821/1940Z @:GB7NOS.#76.GBR.EU #:40085 [Golspie] FBB7.00i $:3E2063GM0CS
From: GM0CSZ@GB7NOS.#76.GBR.EU
To : TECH@WW
Tnx John ,for the design below.
Recently I have had some success with the TVI filter described in the Full
Licence Manual with an added quarter wave stub.
The stub was cut for max attenuation at 144.690 MHz with the aid of a
professional spectrum analyser (Rhode & Swartz)
The problem was an amateur causing TVI to a direct neighbour who had
installed a distribution amplifier (apparently wide band) to distribute
UHF sigs to 3 different TV sets in the house.
The amateur can now use up to 5 Watts on 2m without causing interference.
Note : It is ridiculous that whereas Band 1 TV was abandonned in the UK
more than 25 yrs ago ,these wide band TV amps can still be marketed and
sold in the UK.
If there is another TVI problem affecting amateur operations ,I get
involved in , I shall try the design below.
Tnx for the info
Frank GM0CSZ
=====================================
G8MNY wrote:-
> I have run up to 400W on 70cm & have found this filter design very effective.
> It is basically a suck out filter "T" to the aerial socket, & with effective
> UHF braid breaker. It is differnet than using a 1/4 wave coax stub on 144MHz
> also works on 3x @ 432MHz, but unwanted notch @ 5x 720MHz.
>
> This filter has been made on the spot once, out of a "cat food tin lid" with a
> few components, to successfully solve a 25W ERP 70cms Packet Node TVI case.
The> problems were at a distant neighbour (50M away) to a remote node, were the
TVI
> had been caused by a so called "satellite expert" who had added an unfiltered
> high gain UHF booster amplifier to get TV signals around the house.
>
> This design suits all UHF & VHF bands, just change the number of turns etc...
>
> Band Turns
> 6M 8
> 4M 7
> 2M 5
> 70cm 3
> 23cm 1 make C a 0.5-5pF
======================
73 - Frank , GM0CSZ @ GB7NOS.#76.GBR.EU
Inver by Tain , IV20 1RX Scotland UK Loc: IO87AT
Also in 2005 they say the future is bright ; 2 of its challenges remaining
to be RENEWABLE ENERGY and LINUX.
Message timed: 15:38 UTC on 21 Aug 2005
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