Problems with ra0sms Mini Whip Antenna

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ultravista

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My ra0sms mini whip antenna is ~6 meters high. The first 3 meters is a galvanized steel pipe; the last 3 meters is PVC plastic. The antenna is mounted at the top of the PVC pipe. It is fed with coax. The power unit is powered with 9V 500maH and the ground is connected to the antenna mast.

The noise is terrible and broadcast AM is overloading everywhere.

Compared to a long wire of equal height, the ra0sms mini whip is really under-performing. The noise is excessive and the SDR can barely pull in a signal.

Tuned to the same frequency, the longwire has a strong signal with low-noise and is listenable. The ra0sms mini whip at the same frequency has no signal with high noise and is un-listenable.

With or without the ground attached to the power unit, the noise and signal strength remains the same. The ground from the box is clipped to the antenna mast.

Representative photos tuned 6.060 and 10.000 MHZ.

# 1 - ra0sms 10.000 MHZ
# 2 - longwire 10.000 MHZ
# 3 - ra0sms 6.060 MHZ
# 4 - longwire 6.060 MHZ
# 5 - Antenna mount (you can see the longwire in the tree on the left edge of the photo)
 

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n0nhp

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Amplified antennas in urban/suburban locals are pretty much not usable without heavy filtering especially with the wide open front ends of most SDR receivers.
A quick google will show you are not the only one with the problem.
I have been playing with an amplified antenna that I wrote up in this thread https://forums.radioreference.com/software-defined-radio/354464-lna-portable-antenna-rsp2.html
and note the same thing.
At home with all the man-made noise and local MF stations, I have not been able to use the PA0RDT or the antenna of my own (borrowed constructions details) design.

Bruce
 

ultravista

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An update ...

I powered the antenna with a 9V battery putting out ~ 8.5V. The antenna in its original position (6 meters high). The coax is grounded to the metal mast (the lower portion of the mast) via a barrel connector. The barrel connector is BNC to BNC. The bare metal of the barrel is secured against the bare metal of the mast.

With the 9V battery, I know it is not the power source, and it is grounded to the mast; albeit the mast is sitting on concrete - not a true ground but a decent amount of metal. The ra0sms is so noisy that I cannot tune anything - 100% static.

See the attached photos = you can see the noise profiles across the entire band. The spikes, or peaks in the graphs, are 10 KHZ apart (e.g., 5.000 then 5.010, 5.020 - 10.000, 10.010, 10.020, etc.). This pattern follows the entire band up to 30.000 MHZ. It is so noisy that I cannot tune a single station.

5.000 mhz http://i.imgur.com/HCgkt1r.jpg
10.000 mhz http://i.imgur.com/mUsvPLB.jpg
15.000 mhz http://i.imgur.com/55H4MB0.jpg
20.000 mhz http://i.imgur.com/nILzDiD.jpg
25.000 mhz http://i.imgur.com/iRaNw6f.jpg
30.000 mhz http://i.imgur.com/MddL4Xm.jpg

The long wire antenna at the same height is not exhibiting the same problem. I can tune many distant stations and the noise level is low (acceptable).

What would cause noise at 10 KHZ steps from 0 to 30.000 MHZ?
 

n0nhp

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I don't think building them for sale would be a good fit for me. There are too many people with unrealistic expectations for amplified antennas and I am too old and crochety to try to work through the issues.
That is the reason I posted my experiment, so those that would like to try their own take can take the ball and run. The price of parts is extremely low. The tools needed are minimal, a pair of scissors, a hacksaw, a hand drill and a soldering iron. Probably the most intricate part for me was bridging the capacitor so the Bias-T would power the LNA. Soldering a 9V battery clip on and removing the SMA connectors to solder to the copper foil and the F connector don't take much skill. If you use an SMA to whatever coax connector you decide to use would eliminate the removal and re-install on one end.

I think this antenna from my view will remain an experimental and not a production device ;-)

Bruce
 
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