RA0SMS vs PA0RDT Active Mini Whip - RA0SMS is Very Noisy - Why?

Useful information regarding antennas for SDR products.
ultravista
Posts: 26
Joined: Thu Jun 22, 2017 3:40 pm

RA0SMS vs PA0RDT Active Mini Whip - RA0SMS is Very Noisy - Why?

Post by ultravista » Fri Feb 15, 2019 2:08 pm

Posted byu/ultravista_2
1 day ago
RA0SMS vs PA0RDT Active Mini Whip - RA0SMS is Very Noisy - Why?
I have been using a PA0RDT active mini whip from Roelof Bakker for about a year now. The PA0RDT antenna has served me well. Clean and able to pull in signals that a 260 foot loop and various long wires cannot.

I recently bought a RA0SMS active mini whip from Anton Gavrilov and having major noise issues.

Both the PA0RDT and RA0SMS are powered by a 12v wall wort (same model #), on a non conducting mast @ 20 feet, and fed with 50 ohm coax. The radio is a Yaesu FT-950 with an RSP2 as a panadapter. The 12v power supply is choked with snap-on ferrites.

The RA0SMS produces noise approximately every 10 KHZ - the noise is present from LF all the way through HF. The noise is visible and is rendering the antenna unusable. You can see the noise spikes in the first three photos, and the lack of noise with the second set of three photos.

Below is a comparison on of the two antennas switched through an Alpha Delta 4 position coax switch.

RA0SMS

https://imgur.com/cqhxqw2

https://imgur.com/KAROVeu

https://imgur.com/gzQHoiM

PA0RDT

https://imgur.com/7NiKjLW

https://imgur.com/eldjBSI

https://imgur.com/WKL5dW3

I have swapped the wall warts between the two. Both power supplies are identical. The same noise is present with both wall warts.

I also noticed that non-noise signals, such as broadcast AM, are significantly lower with the RA0SMS. Putting a BC AM filter in-line had no effect on the noise spikes.

What could be causing the noise across all bands with the RA0SMS? All things are equal with the exception of the antenna and power feed unit. The PA0RDT is clean and rarely overloads, even with Broadcast AM, with the Yaesu FT-950.

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g1hbe
Posts: 494
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Location: Cheshire, UK

Re: RA0SMS vs PA0RDT Active Mini Whip - RA0SMS is Very Noisy - Why?

Post by g1hbe » Fri Feb 15, 2019 3:19 pm

Peaks every 10 kHz sounds familiar - where are you located? If you are in the USA, then this may be intermodulation from MW broadcast stations which are spaced by 10 kHz. It sounds like the RA0SMS antenna may be a sub-standard design compared to the PA0RDT.

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Andy

Mike2459
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Re: RA0SMS vs PA0RDT Active Mini Whip - RA0SMS is Very Noisy - Why?

Post by Mike2459 » Fri Feb 15, 2019 5:01 pm

Bigger may not always be better.

The E-Field plate (the antenna) of the RA0SMS appears to be much larger than the MiniWhip. The MiniWhip uses a 30mmX45mm plate. I made the plate on my home built min-whip slightly larger (around 30x50mm) and ended up trimming it down to the recommended size. Occasionally It exhibited the same symptoms as the RA0SMS. It would occur frequently during the gray-line.
PA0RDT.JPG
The MiniWhip
PA0RDT.JPG (88.41 KiB) Viewed 4982 times
RA0SMS.JPG
The RA0SMS
RA0SMS.JPG (53.86 KiB) Viewed 4982 times

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ultravista
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Re: RA0SMS vs PA0RDT Active Mini Whip - RA0SMS is Very Noisy - Why?

Post by ultravista » Fri Feb 15, 2019 5:26 pm

g1hbe wrote:Peaks every 10 kHz sounds familiar - where are you located? If you are in the USA, then this may be intermodulation from MW broadcast stations which are spaced by 10 kHz. It sounds like the RA0SMS antenna may be a sub-standard design compared to the PA0RDT.
Yes, I am in the US. I tried a broadcast AM filter and it had no effect. No visible changes in the waterfall that would indicate attenuation of BCAM.

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ultravista
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Joined: Thu Jun 22, 2017 3:40 pm

Re: RA0SMS vs PA0RDT Active Mini Whip - RA0SMS is Very Noisy - Why?

Post by ultravista » Fri Feb 15, 2019 5:28 pm

Mike2459 wrote:Bigger may not always be better.
Mine is the new RA0SMS with a wire, not a plate. The wire is approximately 5-6 inches long.

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ON5HB
Posts: 140
Joined: Sat Dec 29, 2018 1:07 pm

Re: RA0SMS vs PA0RDT Active Mini Whip - RA0SMS is Very Noisy - Why?

Post by ON5HB » Fri Feb 15, 2019 6:32 pm

I have the mini-whip as well and use it only when there is lightning.
The reason you may not put it on a metal pole is because the coax cable is part of the antenna.
So if you put it on metal pole the pole acts as an common-mode-choke and the "antenna" stops working.

What you do is find a distance of the coax where it works and then put a choke in place to filter out rubbish from house or neighbours.

Also, the bigger you make the plate/wire the worse electric spikes are fed into the receiver.
The plate/wire isn't the real antenna, the coax is mostly. :lol:

So the more the coax can pick up, the more rubbish get into the receiver.

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Mike2459
Posts: 318
Joined: Mon Jul 24, 2017 8:24 pm

Re: RA0SMS vs PA0RDT Active Mini Whip - RA0SMS is Very Noisy - Why?

Post by Mike2459 » Fri Feb 15, 2019 7:14 pm

The plate/wire isn't the real antenna, the coax is mostly.
I don't think you are giving that little copper plate enough credit.

The plate is connected to the gate of the J310 FET. With the Bias-T powered down the FET can't amplify the signal.
Powered down.JPG
Powered down.JPG (138.49 KiB) Viewed 4959 times
Let's apply 12 volts to that amplifier.
Powered Up.JPG
Powered Up.JPG (160.37 KiB) Viewed 4959 times

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g1hbe
Posts: 494
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire, UK

Re: RA0SMS vs PA0RDT Active Mini Whip - RA0SMS is Very Noisy - Why?

Post by g1hbe » Fri Feb 15, 2019 7:45 pm

ultravista wrote:
g1hbe wrote:Peaks every 10 kHz sounds familiar - where are you located? If you are in the USA, then this may be intermodulation from MW broadcast stations which are spaced by 10 kHz. It sounds like the RA0SMS antenna may be a sub-standard design compared to the PA0RDT.
Yes, I am in the US. I tried a broadcast AM filter and it had no effect. No visible changes in the waterfall that would indicate attenuation of BCAM.
The reason for that is that the intermodulation is taking place in the antenna electronics. Once the IMD has happened, a down-stream BC filter won't help.

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Andy

ON5HB
Posts: 140
Joined: Sat Dec 29, 2018 1:07 pm

Re: RA0SMS vs PA0RDT Active Mini Whip - RA0SMS is Very Noisy - Why?

Post by ON5HB » Fri Feb 15, 2019 7:48 pm

Funny.....the amplifier doesn't just amplify 1 pole only.
It amplifies the entire "antenna".

Put a choke-balun/filter right after the connection to the "antenna" then report it still works.

Same as "End-Fed" they stop "working" when being choked at the feeding point.

Never wondered why it must be a non-conducting-pole to place the "antenna"?

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Roger
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Re: RA0SMS vs PA0RDT Active Mini Whip - RA0SMS is Very Noisy - Why?

Post by Roger » Sat Feb 16, 2019 12:28 am

The RA0SMS has been discussed on this forum before. You may find some answers here...

viewtopic.php?f=8&t=1138

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