[NLRS] VHF low pass filters?

Wed Jan 2 11:31:37 EST 2013

That open stub is easier to tune if you make it shorter and tune it with 
a variable capacitor, but the capacitor needs to be in a shield because 
its a very high impedance point and so an effective antenna. A handy 
length is 1/8 wave, 45 degrees because the tuning capacitance is easily 
computed as having reactance equal to the coax characteristic impedance. 
But length with the right capacitor isn't critical. And you can hook the 
stub to your own 6m receiver and tune it for the best notch and not need 
to tune it after application to the TV antenna. 75 ohms at 50 Mhz is 43 
pf, 50 ohms is 62pf. And for a shunt stub the coax impedance doesn't 
matter much, though most TV coax these days has an aluminum foil shield 
so its harder to get a good connection than RG58 or 8X and 8X should fit 
a RG59 75 ohm F connector OK.

73, Jerry, K0CQ

On 1/2/2013 10:23 AM, Phil Hejtmanek wrote:
>
>
> Kirk,
>
> Than makes it sound like the receiver is being desensed by your transmissions, probably by his preamplified antenna.  You'll want to know which channels he experiences this on.  You can look up the stations on the FCC database and find out what the RF channel the signal is on, as the channel number displayed by the receiver is likely a legacy channel preserved for branding purposes.  Most DTV is on UHF or high band VHF (7-13), but believe it or not, there are still some stations saddled with low band VHF channels, which would be especially vulnerable to a 6 meter signal.
>
> The best bet is to try his receiver without the preamp, especially if you are able to receive the same stations without problem.  Failing that, you could try to either filter out your signal or trap it.
>
> If you can get between his antenna and the preamp, you could insert an open quarter wave coaxial stub cut to suck out 50 MHz.  I've done this before and it works pretty good.  All you need is a Tee connector and the coax. Make it long and trim until it works best.
>
>
> 73,
>
> Phil   kf9us
>
>
>> ________________________________
>> From: kp hpjr<inservice2him at hotmail.com>
>> To: p_hejtmanek at yahoo.com; "nlrs at mailman.qth.net"<nlrs at mailman.qth.net>
>> Sent: Wednesday, January 2, 2013 9:57 AM
>> Subject: RE: [NLRS] VHF low pass filters?
>>
>>
>>
>> Phil,
>>
>> He states the nature of the interference to be a scrambling of the picture or pixelating (SP?) of the image.
>>
>> He has said nothing of the sound aspect.
>>
>> I'm sure more info will be coming.
>>
>> The good news here is I have a wonderful relationship with this person. He even helped install my Force 12 HF yagi.
>>
>> KK
>>
>>
>> ________________________________
>> Date: Wed, 2 Jan 2013 07:27:03 -0800
>> From: p_hejtmanek at yahoo.com
>> Subject: Re: [NLRS] VHF low pass filters?
>> To: inservice2him at hotmail.com; nlrs at mailman.qth.net
>>
>>
>> Hi Kirk.
>>
>> Very interesting problem from my perspective; I've been involved in TV transmission for 35+ years, and I think this is the first TVI complaint I've heard about now that the US has converted to digital TV.  I am curious to know what the nature of the interference is, and the actual RF channel that your neighbor experiences it on.  Has he been able to describe the nature of the interference to you?  Is it picture or sound?  More likely than not, you are either overloading a preamp in his antenna system and desensing his receiver( resulting is loss of everything), or your signal is getting in to his TV audio system somehow (if he has an external surround sound system this is fairly likely) and he's hearing artifacts of your SSB modulation in his speakers.
>>
>> I doubt the problem is on your
>   end...more likely he needs some grounding help.  If it is an overload problem, maybe you could put a tuned stub on his antenna line to suck out the 50 MHz signal.
>>
>> Good luck and 73,
>>
>> Phil   kf9us
>>
>>
>>
>>
>>
>>
>>> ________________________________
>>> From: kp hpjr<inservice2him at hotmail.com>
>>> To: "nlrs at mailman.qth.net"<nlrs at mailman.qth.net>
>>> Sent: Wednesday, January 2, 2013 7:03 AM
>>> Subject: [NLRS] VHF low pass filters?
>>>
>>>
>>>
>>>
>>> Group,
>>>
>>> Happy New year.
>>>
>>> A neighbor approached me asking if I was operating the other night. He said that I had been interfering
>>> with his over the air TV signal. He placed the time frames during the MS rally and during this weekend Es opening.
>>>
>>> I have only been on 6m as of late at times running up to 600w. His home is about 1000' away from me. His setup is a new digital TV with outdoor antenna fed with the typical radio shack type coax. His antenna is basically looking my way.
>>>
>>> I'm needing some help with this. Are there filters I/he can use?
>>>
>>> I'm well grounded and use very good hardware...Andrews connectors and feedlines etc.
>>>
>>> Your input welcome.
>>>
>>> Kirk, N0KK
>>>
>>> BTW: 1st RFI complaint in 18 years.
>>>
>>>
>>>
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>>
>>
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