Tom's comments sparked a question. (No pun intended).
Does the SNR of the targeted noise source vs. other signals on the sense
antenna, matter in this application?
Art NK8X
ᐧ
On Sun, Nov 1, 2015 at 12:07 PM, Tom W8JI <w8ji@w8ji.com> wrote:
> I have an intermittent RFI issue that comes from a subdivision about a 1/4
>> mile away. To combat the noise I have been trying to use my ANC4 and I
>> built a sense antenna out of an 80m hamstick that I put 20 feet in the air
>> yesterday for a trial to cancel the noise on 80m (cheap and easy
>> experiment). The location of the sense antenna is at the corner of my lot
>> as close to the subdivision that I can get. The design is the hamstick as
>> a vertical element and two 102 inch whips as elevated radials.
>>
>>
> 102 inch whips would not be an effective counterpoise unless one or both:
>
> 1.) The whips were loaded to resonance with a high Q coil, at which point
> it would be a single frequency counterpoise and still require a good
> feedline choke
>
> 2.) The feedline had a much high common mode impedance than the common
> point impedance of the whips
>
> Without the above, the coax shield is mostly the antenna...not the
> Hamstick. You would have been much better off with a ground rod.
>
>
> The noise is s9 on my 1/4 wave 80m vertical and 160m inverted L. This is
>> a multi band vertical with wires for 40m, 80m & 160m. I also have other
>> antennas such as a 160m 2wl long loop and a trapped dipole. What is
>> interesting is that the noise is significantly less on the loop and the
>> dipole. I attribute this to the noise being vertically polarized based on
>> my research on the internet. Also this sense antenna is roughly 150ft away
>> from the vertical antenna.
>>
>>
> That actual reason for that is the earth acts like a short circuit and
> attenuates any horizontally polarized ground wave.
>
> The low horizontal antennas also have very poor ground wave response.
>
> This combines to make horizontally polarized antennas less sensitive to
> distant ground wave noise.
>
> The issue is the level of the sense antenna noise is significantly less
>> than the vertical and I am not able to find a null point that makes a
>> difference. I can however use the loop antenna and I have enough signal
>> with the hamstick experiment to get a null as the received level of noise
>> on the loop is significantly less. So I believe I need more receive gain
>> on the sense antenna.
>>
>> So with the above in mind, is there a low cost pre-amp that I could use
>> on the sense antenna to boost the signal? Or what other ideas are there
>> for a sense antenna. I don’t want to put up another 1/4 wave antenna for
>> sensing. I have read where folks suggest putting 50 ft leg dipole at 5 ft
>> above the ground for 80m & 40m but I think the noise is vertically
>> polarized and this wont do much but I could be wrong and have been wrong
>> before.
>>
>>
> I would build a ground mounted vertical sense antenna with amplifier, use
> a ground rod as a ground, and decouple the coax near the sense antenna. A
> simple J310 source follower amplifier on a 102 inch whip would have a ton
> of signal level.
>
> 73 Tom
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