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 Post subject: my near-Beverage attempt
PostPosted: Jan Mon 29, 2018 5:46 pm 
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Joined: Jun Mon 24, 2013 3:00 pm
Posts: 987
Location: Champaign IL 61822
I've been plagued with ambient noise.

Yesterday I bought 100 feet of wire and made a poor Beverage antenna.

It had 75 feet of coax leading out the window to the parking lot. There, next to my car,
was a powered (by batteries) preamp with a 6000 ohm input resistance (in parallel
with a few pF.) It was grounded to the car and the 100 feet of wire was laid across the lot and off
into a field. The far end was not grounded so it was not unidirectional. A simulator
says this should have a gain of -5 to -35 dB compared to a dipole in free space.

Compared to all previous antennas, at least at most frequencies, the signal went UP
a bit and the ambient noise went way way down, the S/N radio was up by up to 25 dB!

That is an astounding result! The measured S/N was similar on my Airspy and R390A,
which are my best calibrated receivers.

At VLF and LF the results (where its not a Beverage, of course, which it
ceases to be lower than roughly 60 meters) are super-astounding. The locally
generated noise is GONE, and there are big signals. Signals everywhere. Our local
airport 407 kHz beacon had a 35 dB S/N! There is a digital
signal with 15 dB S/N at about 24 kHz (submarine communications)
There are a dozen reliably decoded DGPS stations!
The 518 kHz naval station on the Gulf Coast decoded nicely.

On the SW bands results were almost but not quite as good.

The downside is that I have to install and uninstall this thing every time I want to use it,
which is of course easy as it just lies on the ground. Other downside: at LF signals are
small and I need a 2-transistor preamp at the receiver to use the Airspy/Spyverter as
the signal is too close to its upconvert frequency feedthrough.
To use my tubized LF (above 190 kHz or so) military set it would not be needed,
nor with my computer sound card below 90 kHz.


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 Post subject: Re: my near-Beverage attempt
PostPosted: Jan Mon 29, 2018 7:24 pm 
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Joined: Sep Wed 10, 2014 2:01 am
Posts: 1695
Location: Costa Mesa, California
I have found that really good receivers can get decent results with many antennas. It is the poor receivers that benefit most from a good antenna.

Norm

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KK6IYM


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 Post subject: Re: my near-Beverage attempt
PostPosted: Jan Mon 29, 2018 7:39 pm 
Member

Joined: Jun Mon 24, 2013 3:00 pm
Posts: 987
Location: Champaign IL 61822
Even the best receiver can't help with locally generated noise.
Lots of gain does not help if the noise goes up in proportion.

An antenna with a good lobe at low elevation angles like
a Beverage helps.

And, of course, you're not going to beat an R390A for a receiver
suitable for discussion around here. (Of course, the first stage of this
affair is an MPS8097, a very low noise transistor, so the radio does not count
for noise even if its an R390A.)


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 Post subject: Re: my near-Beverage attempt
PostPosted: Jan Mon 29, 2018 9:52 pm 
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Joined: Jun Sun 19, 2011 2:31 pm
Posts: 5381
Several years ago I did some work with Beverage antennas and it was an eye opening experience. Even though I have a very quiet rural location the Beverage made a big difference for me on 160 compared to the modified Hy Gain 18HT I use on 160. I got involved with other projects this winter but I had planned to do some experiments with my RAK receiver to see how it would do with LW signals from Europe using a good antenna.

Now I try to check new stuff when it comes into the house to see whether it will be a noise issue so I will at least know what is causing the problem. The charger for my new Canon camera emits a wideband RF "squawk" when it is first plugged in and another when a battery is plugged into one of the charge compartments but otherwise seems to be quiet for the way I will use it. The only time it gets a little noisy is when it is used to discharge a battery and that isn't a function I will need. The worst recent noise generator was a replacement adapter I picked up for an Asus tablet that I quickly replaced with an Asus branded unit. One of the LED bulbs I use over the work bench also got very noisy but then died a short time later so at least it didn't make noise for long before expiring.

Rodger WQ9E


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 Post subject: Re: my near-Beverage attempt
PostPosted: Jan Tue 30, 2018 6:57 am 
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Joined: Aug Fri 29, 2014 6:17 pm
Posts: 2436
A lot of swlers find relief from local noises by doing mini dxpeditions, they drive to some place in the sticks where electrical interference is nil and dx for a few hours. Your effort is likely to be much more oft employed as you don't have to drive anywhere!


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 Post subject: Re: my near-Beverage attempt
PostPosted: Jan Tue 30, 2018 8:49 pm 
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Joined: Mar Mon 17, 2008 5:05 am
Posts: 5201
Location: Ashhurst, New Zealand
Quote:
A lot of swlers find relief from local noises by doing mini dxpeditions, they drive to some place in the sticks where electrical interference is nil and dx for a few hours.


Yup - tried that - about 300yards of telephone wire laid out over our rifle club range on a summer evening - nobody shooting of course! All I got was the infernal ticking from every electric fence for miles around! Noise blanker was just not good enough to kill them!

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 Post subject: Re: my near-Beverage attempt
PostPosted: Feb Sat 03, 2018 5:52 pm 
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Joined: Jun Mon 24, 2013 3:00 pm
Posts: 987
Location: Champaign IL 61822
I've tried the same setup with shorter wires (so not a real Beverage except at 10 meters)
like 30 feet to avoid stringing over the parking lot.

It still works great, the noise remains low and signals good, just not as good
in some cases.

The proof is that using 30 feet last night I got LW broadcast stations at 252 kHz
from both Ireland and Algeria (fading between one or the other). Then they faded out
and I got ... after decades of failed trying ... the BBC on 198 kHz. At times all three
were good enough to hear actual call signs from both on 252 and the phrase BBC
exactly on the hour on 198. I was able to measure the carrier offset between the BBC and
the beacon on the same frequency as 4.5 Hz.


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