Cut the Noise: Listening on Antennas for Other Bands

Maybe so.

 

If you break a scientific "law"--intead of being locked up,
you get to rewrite the law, and it gets named after you!!!

 

I have a vertical doublet like this. I found that I can rotate the Transmitter Matching dial counter-clockwise a few numbers on my MFJ tuner, and sometime pick things out that I wouldn't with the antenna tuned. It works, but for whatever reason, not as well as a different antenna. Not sure why, and haven't tried it enough times to stand behind what I just said.

 

Interesting. Is your vertical dipole fed with a balanced line? Balun at center?
Is the tuner output truly balanced or doe it use a balun and wht type?
A complete diagram of your antenna and matchig network would help.
Thanks, and 73...

 

I run ladder line to the shack, and my MFJ-949C tuner, with internal balun. Haven't tried it on 6 or 10. It does well on 15, 17, and 20. About 1 to 2s down from a 40m 1/4 wave, and is toughest to tune on 40 (I can get down to 1.5 to 1 on this basic tuner, which is likely why). It tunes 80, but haven't been on with it much since putting it up. I am currently building a 3-el yagi, have my moxon down low, and I am using this to suffice, in the meantime.

I just followed this: http://www.dj0ip.de/my-favorite-antennas/all-bands-vertical/

It actually transmits very well on 20 (and probably 15, also). It is only about 1/2 an S down from my moxon, on transmit, but doesn't hear as well. It is noisy, because it's vertically-polarized and I am in the city.

 

Now this makes more sense! HL1ZIX = KE0EYJ

I have a https://www.dxengineering.com/parts/dxe-rf-pro-1b that I mostly used on the lower bands. Worked well there but have loaned it out to someone else so don't have enough experience to comment on it. But what I did like is that it did very well down in the 200-500 kHz range as well a AM broadcasting.


I just watched your video with the KX2. I noticed that you have not tried the NR (noise reduction). I have a KX3 and operate primarily CW, so can't really comment on how well it works on SSB.

But, on CW the NR lets me pull some very weak signals through the noise.

Give it a try on CW and see if switching antennas has the same effect.

 

Can't comment on the KX3, but I find the NR on the KX2 to be a detriment to faint DX. It drops the signal level, and dilutes the signal, compared to not using it. The only rig that I have found the NR is useful on is the ICOM 7300, and that is only with a setting of 1 or 2. I basically leave the 7300 on NR setting 1, at all times.

I mentioned why I do not use NR more than once, at the beginning of the KX2 video. It might be more useful for CW, but I do not know. I do not run CW. It makes sense that it would be more useful on CW.

 

I don't have a resonant antenna for 40 and 80 and live on the edge of town and closely surrounded by houses. Anyway, back late January 2017 with my Yausu FT-450D I worked Stateside with a random longwire antenna using an external ATU.

I had S7 hash noise level right across the band but detected that something was in there up around 3.795 - this being 0230am here in the UK. It was frustrating believe me and was about to give up for the night.

Suddenly, out of this frustration, I flipped the antenna switch to my multiband 10, 15, 20 dipole and bang there he was in the clear at S6 - and no background noise! So by flipping the antenna switch back and forth I made the contact and my overseas friend was none the wiser, giving me in reply 4 by 5 for my transmissions using the long wire.

Now been using this method on 40 and 80 for the past almost two months - not ideal obviously, but it works fine.

 

Just wanted to mention that I built my first 2-el yagi (using modeling software), this past weekend. It is a 15m yagi, and hears better on 20m, than my 2-el 20m moxon, because the moxon is currently too close to the roof, and noisy neighborhood electronics. The 15m yagi is 5m above the roof, temporarily. It is not bothered by so much noise, when listening on 20m.

This seems to work only to the North, because of power lines and a cell tower in that direction. Odd, but I am exploiting it. The moxon is low, because the mast was damaged by high winds, recently. The moxon hears better in other directions.

 

You can say that again! Once you do, you will regret waiting so long...

73, Jeff

 

I been doing the small antenna trick quite some time on 75 meter DX during more noisy times.
There is local area noise and long distance noise.
The long distance noise that comes in at the same angle as the desired signal can't be dealt with except in the receiver, electronically.
The local area noise that masks the desired signal is dealt with by using a short antenna that picks up less of it.
No real secret here.
On 75 meters, the Mosley Tri Bander cuts the local noise considerably.
It's close by right in the same area with the tower less than 10 feet away from dipole center and higher than the dipole, no less.
You have to keep the two sources separate as to which is the cause of the greater noise.
If the short antenna does not help, the noise is coming in long distance and you can't do much about it with an antenna change. The signal and the noise can't be separated by the receiver. It can't differentiate between the two within the same pass band and improve the signal to noise ratio at the same time..
Good luck.

 

Exactly.

Resonance has squat to do with anything.

The real effect(s) going on are the bandpass or preselection effects of the antenna.

Its easy to make a receiver work with one signal on a bench. Its a whole nother ballgame to have a receiver reject every other radio signal except the one you want.

Two kinds of noise in a RX, noise generated external to the rig (qrm/qrn) and noise generated internal to the rig (intermod and desensitization)

Some antennas have a frequency response that keeps the frequency's causing intermod or desense from getting to your receiver. A common area here is a vhf receiver that overloads on a discone type wideband antenna, but works perfectly with a narrow band yagi. A "antenna tuner" may, in some cases, provide enough preselection (reject off frequency signals) to provide a tremendous difference.

Qrm/qrn is eliminated by antennas that have directivity such that signals from different directions are received differently.

There is also polarization to consider.

Notice either effect has nothing to do with antenna resonance or lack thereof.

In any case, different antennas work differently. My standard advice is get a switch that let's you change antennas on the fly.

Sometimes the best or right antenna really isn't.

Couple tips on receivers, if noise moves you s-meter turn off the preamp, turn on the attenuator, and turn down the rf gain untill it does not.

And search for my post on "measuring the effective sensitivity of a receiver" to learn how to measure your real word hooked to a antenna sensitivity.

Rege

 

If the feedline should become unbalanced, it could pick up local or off-pattern noise.

 

have you ever tried to use the AGC-Slow ? - many times this also helps on ssb signals.

rgds.. OU2V / OZ1FJB