My Diveristy Adventures

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My Diveristy Adventures

Postby KC3JVE » Sat Mar 09, 2019 12:18 pm

Ok, so here it is, two things...

Number 1: I live in an urban environment and deal with a TON of noise. I have a 10 over to 20 over 9 noise floor on 75m. I have been able to locate the noise source to my neighbor, but I don't know them and I haven't approached yet. So anyway, I made up a 200' "diversity" antenna, an 18awg piece of insulated stranded copper wire, soldered to the center conductor of a PL259, using an adaptor, going into rx2. I was able to get the signal of the noise source as loud as 40 over 9. But one thing I have noticed about diversity, is that no matter what, You can get rid of the noise and drop the noise floor, but signals that are on the band, do not "come out of the noise". The signal to noise ratio either stays the same or I can completely phase all noise and signals out. I am using Rx1 & RX2 as my receiver source and im using RX2, that is set on ADC 2, for my reference source. So basically, I can get rid of the annoyance of the interference, but unfortunately, im not able to hear stations with diversity enabled, that I was previously unable to hear with it disabled. Thats what I was hoping for. I was hoping I could utilze Diveristy to help with DX stations or stateside stations that were right at my high noise level. And If I could drop the noise even 2db, and not effect the signal of the incoming station, that would be amazing!

Number 2: Transmitting with diversity enabled... I CANNOT transmit with my diversity antenna connected to RX2, due to excessive RF coming back in the shack and overloading ADC2. Doesn't matter if I have the amplifier or not. Doesnt matter if diveristy is enabled or not. I have to disconnect it from RX2 before I transmit. The diversity antenna is 40' away from the transmitting antenna. Any videos or tutorials Ive ever seen, only discus the receive side of things. I have auto mute RX2 on TX selected as well.

So, am I doing something wrong?

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Re: My Diveristy Adventures

Postby K9RX » Sat Mar 09, 2019 1:53 pm

Scott will I'm sure reply about using the system in general. I have never been able to get diversity to work myself but that is more because the antenna selection is critical. I've not had a reference antenna that picked up the noise as loud or louder and still picked up some of the signal. So I end up with the same results you have which are not real diversity as I understand it. It DOES work - just needs the right antennas.

As for xmit - there's an option to "GND RX2 ON TX" that has to be checked! Its under GENERAL and then one of the tabs down the line a bit somewhere around "Filters" ... I'd suspect you do not have it checked.

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Re: My Diveristy Adventures

Postby W1AEX » Sat Mar 09, 2019 10:19 pm

Hi Perry,

I'm not sure which ANAN hardware you are running but as Gary said, the RX2 port needs to be switched away from the antenna and grounded when you transmit. Some of the ANAN hardware does this internally, but some of it does not. My ANAN-200D does not ground the RX2 port so I use an external relay to handle that task automatically when I am transmitting.

The gain and phase adjustments in the "Diversity" feature work together so a systematic approach is helpful. Also, most of us have found that you can only put a dent in one noise source at a time. The video below shows an S-9 +10 oscillation that I encountered on my panadapter from the power supply of my new Netgear router. Adjustment of the Gain and Phase controls eliminated it completely with my main station wire antenna (178' center-fed dipole with open-wire feedline) used with RX1 and one of my 85' vertical/triangular receive loops used with RX2. For better or worse, the video below shows how it works here. I ended up filtering the router's power supply and that was the permanent solution for this one.



"One thing I am certain of is that there is too much certainty in the world."
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Re: My Diveristy Adventures

Postby w-u-2-o » Sat Mar 09, 2019 10:39 pm


There are a few things that might be going wrong.

1. I immediately started thinking that you might have ADC1 assigned to both RX1 and RX2 but you explicitly say that's not the case, so I'll assume that's not the problem.

2. You believe the noise is coming from your neighbor. I'm not so certain. It would be really unusual to have man-made noise that is so broad it is taking out the entire band. If what you are really hearing is atmospheric noise then it cannot be eliminated by using diversity. This is because diversity is not what you think it is, it is actually coherent beamforming that is erroneously labeled as "diversity". Did you read my "sticky" thread on this? I would have to say this is the most likely problem.

As Rob alludes to, there are many types of noise. The only type of noise that "diversity" can eliminate is that of an actual interfering signal that comes from a point source and arrives from a single direction, and these properties are what gives it something we call "coherence" across multiple receiving antennas and receivers. Atmospheric noise does not have coherence, it is random and at any instant of time different at each antenna. You can't eliminate that kind of noise. Similarly, if you have power line noise arriving from a long, distributed source like, you know, a power line, you won't be able to eliminate that, either.

3. When using "diversity" you are trying to steer an antenna pattern null in the direction of the interfering signal and an antenna pattern lobe in the direction of the desired signal. If your antenna geometries are not correct then you can't achieve this.



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