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

[ultravista]

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 100 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

Imgur

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.

 

[RFI-EMI-GUY]

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 100 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

Imgur

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.

Can you zoom in to say a bandwidth of 1 MHz or 500 KHz to see if the frequency of the spikes are stable?

Then try touching the whip, the power supply and feedline to see if there is interaction. If the antenna or feedline change the frequency, you have an amplifier oscillation. If the power supply is sensitive, perhaps to touch or heat applied, then it is the power supply.


Bear in mind that a SDR without any preselector filter is susceptible to overload and wild things can happen.

I am not crazy about the naked SDR receiver craze. A preselector will improve your reception greatly.

Edit: I read you have a Yaesu receiver, so I assume it already has preselection as best practice.

Sent from my SM-T350 using Tapatalk

 

[AB4BF]

Have you tried reversing the wall wart plug in? The blades are usually not polarized.
Try that first before you put choke(s) on the power cord.
Good luck.

 

[RFI-EMI-GUY]

Have you tried reversing the wall wart plug in? The blades are usually not polarized.
Try that first before you put choke(s) on the power cord.
Good luck.

Thats a very good suggestion.

 

[ultravista]

Here are four additional screenshots A & C are with the power supply one way (normal) and B & D plugged in the opposite way (upside down).

A

B

C

D

There appears to be no effect by changing PS polarization.

 

[RFI-EMI-GUY]

Actually there is a difference.

Sent from my SM-T350 using Tapatalk

 

[ultravista]

Between A & B, what is the difference?

 

[RFI-EMI-GUY]

Between A & B, what is the difference?

None but why show C&D?

 

[ultravista]

C & D show the signals closer, less zoom than the other examples.

 

[nanZor]

You know that after more than 1 or 2 years worth of this same question being cut-n-pasted over on QRZ, Reddit, and other hf forums, it starts to *read* like a PA0RDT antenna fanboy thing. Not sure if you've hit up the HFunderground forums yet.

So I get it - let's trash the RA0SMS antenna in comparison to the PA0RDT.

WAIT - instead of doing that, how about *HELPING* current RA0SMS antenna owners by trying to make yours work better, rather than push the 'RDT. Plenty of suggestions in the other forums have been made. Let's start there.

I don't object to your observations - but after some point where you let us all try to help with ideas and suggestions for years about the RA0SMS, going over the same old things, just *reads* like a back-handed sales pitch for the PA0RDT, with the users offering suggestions being used to do the trashing.

Then again, I can point to other sites that have experience with the PA0RDT that aren't so happy with that too. Let's not go there shall we?

Instead, let's help and try to make the most out of *BOTH* units.

 

[nanZor]

How to help BOTH the RA0SMS and the PA0RDT:

1) Power supply. Must be clean. Should be regulated. A wall wart with a few turns around a snap-on ferrite does NOT cut the mustard. Nor does a 9v transistor radio battery cut it (often at 8v or lower once a load is applied). You have to get REAL.

Unless you know, and can STATE what supply you are using, we have no way of knowing if one is shooting themselves in the foot at the start. Although it may seem like overkill, a linear ASTRON 4A would be a guaranteed way to ensure you have a clean supply. If you want to adjust voltages, say between 9-12v to play with gain, then there are others available.

BUT, just because the supply you are using with your 'RDT *may* be a problem with the SMS, does NOT mean that you are getting the best out of the RDT!

If we don't know what you are using, then game over from the start - for BOTH units. Just doing an A/B with a wall-wart does not count.

2) Common mode problems with coax:
Like ALL antennas that use coax, you are likely to have common mode issues, that can be a problem (whether heard or not!). Whether or not you believe that the coax is or isn't part of this family of antennas, there is no reason not to follow good procedure.

That is, don't take the chance of the common-mode noise from your house traveling right past your clean power supply and into the antenna.

Until you have taken steps to separate antenna common mode problems, and house-generated common mode problems, you are just shooting blanks. And no, a snap-on, or ferrite of the wrong material is not effective. Here is a good tutorial to get one started:

http://audiosystemsgroup.com/NCDXACoaxChokesPPT.pdf

How to cure: Let's choke right at the feedline leading up to the mini whips. Being so sensitive, you need GOOD chokes. Not just house walls. What a joke.

Use an inline ferrite choke. MFJ 915's are common. Even better are more serious types like the Myantennas CMC-0510-R. Place this after your receiver on a small jumper. Of course the choking materials and methods described in the article above are great for diy'ers.

Get another choke: Place *another* one where the feedline meets the ground under the whip.

But I already have a ground rod as per the instructions !!

A single ground rod does not always make for an effective ** RF ** ground. Hence the chokes on both sides of that ground rod - one at the receiver side, and one down at the ground below outside. Especially important if you don't actually have any ground rod at all.

Only now can we start to get somewhere. Hopefully this will help owners of both the RA0SMS and the PA0RDT.

 

[nanZor]

Re - your 950 power supply:

Unless you are using a wall-wart to power your 950, why aren't you using the supply for the 950? Surely that should be better.

Is the PA0RDT spewing out junk that the RA0SMS is picking up?

Have you tested with the 'RDT powered off? And if we're going to do A/B, I think we should start on the same playing field by removing the 'RDT, and putting the 'SMS on the same mast instead and see.

Do you have a defective unit? Can you exchange it for another one and test again?

Since the PA0RDT and the RA0SMS belong to the same family, perhaps we can learn something indirectly to help the SMS here:

How DOES the PA0RDT Mini-Whip work

To be fair, I don't like the reviewers choice of receivers - I would rather have seen a real communications receiver, not a handheld unit prone to overload in the first place. And while the issue of common mode choking being suggested as being ineffective from an antenna standpoint alone, surely attenuating common mode signals coming *from* the house and much closer to the antenna outside is a good thing - as it would be with any antenna.

Have you employed any of the techniques suggested in the other forums that was asked with exactly the same wording, and what are the results?

The point here is that someone with no discretionary income may have received the RA0SMS as a gift. Why don't we help them rather than just point out the shortcomings?

And of course I take issue with this statement:

Clean and able to pull in signals that a 260 foot loop and various long wires cannot.

For you perhaps. Certainly not for me. Let's get to work and make somebody's day a little brighter with solutions.

 

[ultravista]

hertzian, I just today saw your post, I am not receiving email notifications.

I will first start with powering both antennas with the Astron 35M. That should help narrow down the noise at the power feed point.

My coax is choked via approximately 12 turns around a FT240-43 ferrite. The USB cable too is wrapped around the a *43 ferrite toroid.

I am not sure if your frustration is pointed at me or others; hopefully not me. I am trying to understand why the RA0SMS at my location doesn't perform as it does for others elsewhere. I've tuned Kiwi SDRs claiming to use the RA0SMS and I none exhibit the same behavior. Of the three Kiwi SDRs I found, all are in Europe.

What I don't understand is why the repeating pattern of noise is present on the RA0SMS and not any other antenna. I purchased two RA0SMS - both have the same noise profile. I also have two PA0RDT and neither have the 'problem'. Broadcast AM filters have no effect in reducing the noise with the RA0SMS.

I had a RA0SMS about a year ago and had the same problem. Sold it locally and bought a PA0RDT. Wanting another active antenna, I purchase the 2nd and 3rd RA0SMS this year (one for a friend) hoping that the first one was flawed.

One of the two RA0SMS antennas was for a friend also in Las Vegas, but approximately 20 miles from my QTH. He too had the same noise when feeding his Grundig portable radio. His is a non-conductive mast at ~30 feet. This leads me to believe there is something wrong with both of these antennas.

 

[majoco]

Tried a different computer and or display? I have to use a laptop with my Winradio g33ddc and not on charge. I get broadband interference from about 8.5MHz to almost dead-on 12MHz that comes down the phone line to my VDSL router - it raises the background noise by 10 to 15dB - I can't get rid of all of it but most of it goes if I disconnect the router from the phone line and turn everything else - computer, display, printer, router - off. The phone line goes through the roof space almost parallel to my antenna and probably 12 feet away.

This probably doesn't answer your question - you do have to persevere.

 

[ultravista]

I thought it was my local environment until I ordered the 2nd one and the other for my friend. He is approximately 20 miles from me and having the same noise problem spaced @ 10 KHZ. His is a direct connect to a Grundig portable radio.

 

[majoco]

Ultravista - you are running two parallel posts here - do you expect different answers?

 

[ultravista]

My other post is not mini-whip related but one of QRM present on my SDR as well as other geographically distinct SDRs. This QRM is present on a random length long wire @ my QTH. The two topics are QRM related but not the same.

 

[nanZor]

Well from what I've read, the SMS may be even hotter than the RDT. Which means perhaps that when using the SMS one should decrease the receiver's rf-gain moreso than the RDT?

Does your friend running the Grundig use the dx/local attenuator switch? Does it make a difference? Is the remote sdr overdriving his?

Tip: type 43 ferrite is really for about 15 mhz and above, and are pretty ineffective below that, so perhaps consider switching to type 31 or others with a lower frequency spec. For me, type 43 is 30-300 mhz, so not really hf-worthy in my mind unless you absolutely bury the cable with it.

I have no problem with you personally, not at all.

I'm kind of burnt out on the whole thing now actually, and am too tired to read across all the other forums for followups. Might have been best to keep it to just one, maybe two forums at most.

So here we go again - since these little amps are obviously different in performance, what happens when you reduce the rf gain / and or use an attenuator with an SMS?

Basically, we're putting the ball in your court now. Tell us what YOU have done to improve the situation, given all the feedback from others. Maybe the guy who makes the SMS would appreciate it, and incorporate a fix or note in documentation ...

 

[nanZor]

BTW - your antenna pics ...

I forgot what forum I saw it on where you posted a pic of your setup. Is your SMS / RDT still mounted just outside of the house doorway only a few feet above the roof? If so, that's not the recommended setup, so I'm sure that has been changed to what they recommend.

And looking for a common link here too - any chance of the internet router beating agains the SMS? Cellphones laying close by? Stuff like that.

But for sure, the latest pic of the install would help out.