Date   

Re: HF LOOP

Martin - G8JNJ
 

Hi Paul,

I don't disagree with anything your say.

When comparing waterfalls or spectrum displays it's sometimes useful to set the noise floor on the display so that they are all equal, regardless of the antenna or RF gain, then set the amplitude scales so that they all show the same number of dB per division. That way you can more easily compare the different S./N ratios.

More objective methods are to compare digital modes such as PSK, WSPR and FT which provide a S/N value for each signal received. as long as you compare the same callsign in the same time slot against each other, you should be able to obtain sensible values.

Regards,

Martin


Re: HF LOOP

Paul Newland
 

Hi Martin
I am grateful for your interest and truly respect what you have had to say. I would like to address the comments that you have kindly offered and so will offer a little clarification, that I believe is best made by addressing your individual observations, that I hope you will not object to me quoting below, in parenthesis.

(Looking at your screen grab and based on the waterfalls, I'd say that the middle is providing the best Signal to Noise ratio of about 20dB, the top is the next best with a S/N of about 10dB and the bottom has a S/N of about 8dB).

The top one is my Wellbrook ALA1530LN on the HiZ Port of a SDRPlay RSPduo (Master), the middle one is the Slave receiver fed by the CCW loop-amplifier and the bottom one is a 20M longwire (with tuner). 

The loops are only about 2M apart (not from choice), currently in a N/S orientation and are both centered about 1.5M above ground level.

(However you are not really comparing like with like, as all the receivers have different gain settings and two of them have also got decimation enabled).

The settings for all three rx's  were configured each for their individual optimum performance in the prevailing conditions and confirms my opinion that the CCW was the best performer at the time. I would however, like to emphasise that generally the performances of this and the Wellbrook are pretty close and under other conditions the results may well have been different with the Wellbrook often providing the better SNR, albeit with less gain (but not always) and over their common frequency ranges I prefer to use the CCW (but it's good to have a choice).
In this mode decimation wasn't available (?) for the RSP2 , which is the third/lower one.

Unsurprisingly perhaps the tuned longwire  provides more gain within it's range, but is always noisier.

(Comparing antennas is quite difficult, as variations in propagation, angle of arrival and antenna pattern all complicate the issue).

I do not have the knowledge, by a very long shot, the experience, or equipment to conduct a proper test and would really appreciate it if someone were to do one.

This was the best that I was able to achieve at that time and in the prevailing conditions, within the limits of my ability and setup - the ultimate caveat.

 I have a lot to learn with regard to SWL (I have been forced to learn morse code) and at 81, probably not that long to do so, when time is shared with diving and domestic trifles; although come to think of it, having been naughty enough to survive this long I may well have plenty of time on my hands whilst effectively being confined to property for an indefinite time....

Anyway, thank you again for taking the time to comment.

Best Wishes
Paul





On Tue, 17 Mar 2020 at 10:05, Martin - G8JNJ via Groups.Io <martin_ehrenfried=yahoo.com@groups.io> wrote:
On Tue, Mar 17, 2020 at 08:30 AM, Paul Newland wrote:
I should have clarified that: top to bottom are Wellbrook (SDRplay RSPduo -M), CCW, (Rspduo - s) and longwire (RSP2)
Hi Paul,

Are you sure about this ?

When receiving signal you are always trying to maximise the wanted signal, and minimise unwanted ones (including noise). Lots of folks concentrate on the overall signal strength, but it's the Signal to Noise ratio that matters.

Looking at your screen grab and based on the waterfalls, I'd say that the middle is providing the best Signal to Noise ratio of about 20dB, the top is the next best with a S/N of about 10dB and the bottom has a S/N of about 8dB.

However you are not really comparing like with like, as all the receivers have different gain settings and two of them have also got decimation enabled.

Comparing antennas is quite difficult, as variations in propagation, angle of arrival and antenna pattern all complicate the issue.

As Chris has already mentioned the MLA-30, has a few failings, one of which is limited common mode suppression, which means that the coax cable is often picking up more signal than the actual loop part. It also has a fairly poor frequency response and IMD performance, and can easily be overloaded, especially if the gain is increased too much, producing lots of spurious signals that my not be present when using other antennas.

Some notes on the MLA-30 and other active antennas can be found on this webpage.

https://www.g8jnj.net/activeantennas.htm

Regards,

Martin













Re: HF LOOP

Martin - G8JNJ
 

On Tue, Mar 17, 2020 at 08:30 AM, Paul Newland wrote:
I should have clarified that: top to bottom are Wellbrook (SDRplay RSPduo -M), CCW, (Rspduo - s) and longwire (RSP2)
Hi Paul,

Are you sure about this ?

When receiving signal you are always trying to maximise the wanted signal, and minimise unwanted ones (including noise). Lots of folks concentrate on the overall signal strength, but it's the Signal to Noise ratio that matters.

Looking at your screen grab and based on the waterfalls, I'd say that the middle is providing the best Signal to Noise ratio of about 20dB, the top is the next best with a S/N of about 10dB and the bottom has a S/N of about 8dB.

However you are not really comparing like with like, as all the receivers have different gain settings and two of them have also got decimation enabled.

Comparing antennas is quite difficult, as variations in propagation, angle of arrival and antenna pattern all complicate the issue.

As Chris has already mentioned the MLA-30, has a few failings, one of which is limited common mode suppression, which means that the coax cable is often picking up more signal than the actual loop part. It also has a fairly poor frequency response and IMD performance, and can easily be overloaded, especially if the gain is increased too much, producing lots of spurious signals that my not be present when using other antennas.

Some notes on the MLA-30 and other active antennas can be found on this webpage.

https://www.g8jnj.net/activeantennas.htm

Regards,

Martin













Re: HF LOOP

Paul Newland
 

Re: my last, silly old man - I should have clarified that: top to bottom are Wellbrook (SDRplay RSPduo -M), CCW, (Rspduo - s) and longwire (RSP2)
Best Wishes
Paul


Re: HF LOOP

Paul Newland
 

Hi All
I'll keep this short.
I am a virtual know nothing, but am currently using the CCW HF/VHF loop antenna amplifier, powered by an SDRplay RSP's Bias-T.
The head unit is attached to a 1M aperture, square copper pipe (15 MM diameter), mounted close to (circumstnces) a Wellbrook ALA1530LN on the same approximate orientation, at a height of around 1.5M above ground level,
I also have a 20M, end-fed longwire at about 7M agl (strung  approximately N - S.
The attached image provides a fair comparison of their relative performance in the prevailing conditions this morning, about 130M up on a South-facing hillside in South Devon.
Noise figures not shown as I haven't the screen space to permit with all three RX's running, However, the general SNR's from best to worst, are 1. Wellbrook, 2. CCW (but often a bit of a toss-up with "1" and lastly, 3. The longwire, which, using an ae tuner provides the strongest signal.
Best Wishes
Paul


Re: HF LOOP

Oene Spoelstra
 

In my case the update works very well ! Indeed very sharp nulls and rejecting noise that good so i can use the 75 cm diameter loop indoors situated in front of the window !

Op ma 16 mrt. 2020 21:17 schreef Chris Moulding <chrism@...>:

I'm rather surprised that you did not see the improvement to the HF performance that the upgrade kit makes to the original VLF/HF amplifier. It may be worth trying the antenna again but in a slightly different location.

The signal level from a small loop at HF is very small and needs amplification with a very low noise amplifier. The outer shield of the coaxial cable connected to the loop can act as a very effective HF antenna and produce a very strong signal at the amplifier output socket many dB stronger than that appearing at the loop.

A good common mode filter is required at the amplifier output socket to stop the high RF level bypassing the amplifier and getting into the amplifier input.

One test of how well this works is to look at the depth of the nulls of the loop. As others have already commented a loop antenna made with the Loop Antenna Amplifier gives very deep nulls.

Another possibility for the MLA-30 to appear to have a better performance is if the signal appearing on the coax is totally overpowering the wanted signal from the loop. In that case you don't have a loop antenna you have a long wire antenna!

Regards,

Chris


Re: HF LOOP

Chris Moulding
 

I'm rather surprised that you did not see the improvement to the HF performance that the upgrade kit makes to the original VLF/HF amplifier. It may be worth trying the antenna again but in a slightly different location.

The signal level from a small loop at HF is very small and needs amplification with a very low noise amplifier. The outer shield of the coaxial cable connected to the loop can act as a very effective HF antenna and produce a very strong signal at the amplifier output socket many dB stronger than that appearing at the loop.

A good common mode filter is required at the amplifier output socket to stop the high RF level bypassing the amplifier and getting into the amplifier input.

One test of how well this works is to look at the depth of the nulls of the loop. As others have already commented a loop antenna made with the Loop Antenna Amplifier gives very deep nulls.

Another possibility for the MLA-30 to appear to have a better performance is if the signal appearing on the coax is totally overpowering the wanted signal from the loop. In that case you don't have a loop antenna you have a long wire antenna!

Regards,

Chris


Re: HF LOOP

Paul Gulliver
 

Hi Chris,

As you know from my previous posts some weeks ago I will have to disagree with your 1st statement, I done all the mods and was disappointed with the results and the CCW amp is now confined to the surplus draw.
I continue to use the MLA-30 although I have to admit I do get a lot of QRM, whether is directly related to the poor amp or not I can't say.

Regarding your 2nd statement, first I should say I know nothing about the theory behind loop amplifiers, but I don't understand how the amplifier (mounted on the loop itself) can filter out C/M noise and signal present on the coax when the coax is on the receiver side of the amp - I must be missing something here.

Perhaps one day I give the CCW amp another go and get better results

Paul


On 16/03/2020 at 18:02, Chris Moulding <chrism@...> wrote:
You will see a difference on HF after you have done the upgrade.

The reason that the any loop used with the Loop Antenna Amplifier is directional and has deep nulls is because the common mode noise and signal present on the coax cable is correctly filtered out before it can reach the amplifier.

The MLA-30 is quite poor in it's common mode rejection so that noise and signals picked up by the coax effectively fill the nulls.

Regards,

Chris


Re: Loop Antenna Amplifier - Service Bulletin 4 - HF performance improvement

Chris Moulding
 

It looks like something with a switch mode power supply nearby. Try running your PC on it's internal battery if it's a laptop. Try disconnecting and chargers or other power supplies to see if the noise disappears.

Regards,

Chris


Re: HF LOOP

Chris Moulding
 

You will see a difference on HF after you have done the upgrade.

The reason that the any loop used with the Loop Antenna Amplifier is directional and has deep nulls is because the common mode noise and signal present on the coax cable is correctly filtered out before it can reach the amplifier.

The MLA-30 is quite poor in it's common mode rejection so that noise and signals picked up by the coax effectively fill the nulls.

Regards,

Chris


Re: Loop Antenna Amplifier - Service Bulletin 4 - HF performance improvement

@sdoros
 

I have a RSPDuo and a lot of noise from FM stations when I use loop antenna amplifier from 1.8Mhz till 18Mhz. I have tried feeding the amp via bias tee and via indor unit. Also tried with an external FM notch filter alonf with RSP fm filter. No change, noise is still there.
Any recomendations how to vanish this noise?


Re: HF LOOP

Tom Crosbie G6PZZ
 

I think you might be missing a point here. The fact that your CCW loop is very directional is one of the main points of its use. The MLA-30 is not directional therefore picks up signals from every direction, therefore combining all the signals and perhaps sounding louder. It’s a bit unfair to compare the two if you haven’t performed the necessary upgrade. You’ve not mentioned the receiver you are using or the type of signals you are trying to receive.

I don’t own either of these loops so have no axe to grind either way.

Tom G6PZZ

 

From: CrossCountryWireless@groups.io <CrossCountryWireless@groups.io> On Behalf Of chipbutty via Groups.Io
Sent: 16 March 2020 16:19
To: CrossCountryWireless@groups.io
Subject: Re: [CrossCountryWireless] HF LOOP

 

I never had much luck with my VLF/HF unit. I tried it with the included wire and a 1m wide copper loop. Like many others with the MLA-30 I found the MLA-30 to out perform the CCW loop on Shortwave. Added to that I found the CCW loop very directional and I was forever messing around with the orientation to tune the signal. I don't have to do that with the MLA-30. This is a big deal for me. I have the MLA-30 fixed onto the back of a chair in my bedroom next to the window and I rarely need to move it to improve a signal. Clearly it does work well for many. Initially my CCW loop outperformed the MLA-30 below 7 MHz but a quick fine tune of the pot on the MLA-30 quickly fixed that. I have not yet done the upgrage mod on my CCW. I'll do that before finally giving up hope!


Re: HF LOOP

chipbutty
 

I never had much luck with my VLF/HF unit. I tried it with the included wire and a 1m wide copper loop. Like many others with the MLA-30 I found the MLA-30 to out perform the CCW loop on Shortwave. Added to that I found the CCW loop very directional and I was forever messing around with the orientation to tune the signal. I don't have to do that with the MLA-30. This is a big deal for me. I have the MLA-30 fixed onto the back of a chair in my bedroom next to the window and I rarely need to move it to improve a signal. Clearly it does work well for many. Initially my CCW loop outperformed the MLA-30 below 7 MHz but a quick fine tune of the pot on the MLA-30 quickly fixed that. I have not yet done the upgrage mod on my CCW. I'll do that before finally giving up hope!


HF LOOP

Brent Mcl
 

Well was messing around with my loop today and change out the wire to 3/8 copper very impressed i highly recommend same dia as wellbrook .


Re: Hi Z Antenna Amplifiers

Chris Moulding
 

I've been surprised at the amount of advice and help following my post on the Topband contesting email reflector. I've had several direct emails with advice too.

What I'm proposing to manufacture is a Hi-Z antenna amplifier. This is is designed to be used with a 5m vertical element (aluminium tube or wire up a fishing rod and a ground or earth rod into the ground. This antenna arrangement can be used on it's own as a low noise receive antenna or with anywhere from 2 to 9 identical antennas in a phased array to produce a steerable directional beam for DX work on 160 or 80m (or the other HF bands).

The amplifier has to have a very accurate and repeatable gain and phase relationship between input and output so that users only have to adjust the coax lengths between several antennas and a central switching unit to construct a phased array.

It also has to have the highest IP3 performance possible so that it isn't overloaded by local medium wave stations.

I've built a prototype using a recently introduced IC from Analog Devices originally intended as a high IP3 buffer stage in front of ADCs in SDR receivers or similar products. During initial testing at the workshop signal to noise tests on a local medium wave station 20 miles away are the highest of any antenna I've tested there.

The design will allow it to be used with 12V or 5V bias tees and there will be two options 75 ohm F type or 50 ohm BNC connectors.

The production PCBs are being designed over the next few days so I expect to have some ready for sale in about a month.

The amplifier will be mounted in the same polycarbonate box used for the Loop Antenna Amplifier and I'm aiming to sell it at the same price.

Regards,

Chris


Re: Hi Z Antenna Amplifiers

Bob G3REP
 

There have been some quite detailed and amazing contributions. Very informative with a lot to learn.

73s
Bob
G3REP


Re: Hi Z Antenna Amplifiers

David Cutter
 

Yes, it's been pretty active for a few days now. I hope he does well out of it.
David G3UNA

-----Original Message-----
From: CrossCountryWireless@groups.io [mailto:CrossCountryWireless@groups.io] On Behalf Of Bob G3REP via Groups.Io
Sent: 14 March 2020 12:43
To: CrossCountryWireless@groups.io
Subject: [CrossCountryWireless] Hi Z Antenna Amplifiers

Good to see that Chris is getting some useful information from the Topband Community on the design of this amplifier.
http://lists.contesting.com/archives//html/Topband/2020-03/msg00109.html
73s
Bob
G3REP





--
This email has been checked for viruses by Avast antivirus software.
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Hi Z Antenna Amplifiers

Bob G3REP
 

Good to see that Chris is getting some useful information from the Topband Community on the design of this amplifier.
http://lists.contesting.com/archives//html/Topband/2020-03/msg00109.html
73s
Bob
G3REP


Re: Coronavirus preparation at Cross Country Wireless

Ed Pusey
 

Be well. A lot of us will be looking forward to more of your products!

Hope all in the UK make it through okay.

Ed P.

On Tue, Mar 10, 2020 at 11:26 AM Chris Moulding <chrism@...> wrote:
Looking at the latest news it's likely that the UK will go into a form of self-isolation to reduce the spread of the coronavirus (COVID19) in about 10 to 14 days. All of us here are in the "at risk" category so we will be taking any measures seriously.

In preparation for this we are trying to get all existing orders shipped this week and next.

We have also reduced the range of products available in case we have to reduce the amount of time in the workshop.

We are also building large batches of our popular Loop Antenna Amplifiers and HF/VHF/UHF Multicouplers so that we will be able to ship them if postal or courier services are running..

Obviously we can accept no special or custom orders until the situation is clearer.

Personally I've already made some preparations to use any enforced leisure time to design some new PCBs for our existing and new products.

Regards,

Chris



--
Ed Pusey

esptwo@...


Coronavirus preparation at Cross Country Wireless

Chris Moulding
 

Looking at the latest news it's likely that the UK will go into a form of self-isolation to reduce the spread of the coronavirus (COVID19) in about 10 to 14 days. All of us here are in the "at risk" category so we will be taking any measures seriously.

In preparation for this we are trying to get all existing orders shipped this week and next.

We have also reduced the range of products available in case we have to reduce the amount of time in the workshop.

We are also building large batches of our popular Loop Antenna Amplifiers and HF/VHF/UHF Multicouplers so that we will be able to ship them if postal or courier services are running..

Obviously we can accept no special or custom orders until the situation is clearer.

Personally I've already made some preparations to use any enforced leisure time to design some new PCBs for our existing and new products.

Regards,

Chris

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