Date   

Re: Tips to improve LAA+ Performance?

Eric Inloes
 

On Fri, Dec 4, 2020 at 01:34 AM, Chris Moulding wrote:
From the description of the extra noise on the coax cable mentioned earlier it may be caused by a poor shield connection between the coax cable and the connector.

This will allow the cable to act as an antenna picking up a lot of local RF noise while still appearing to work with the antenna or amplifier.

While we are talking about loops and their construction don't forget the cardioid loop design I recently posted. It's the one I'm now using as the reference antenna at the workshop due to it's directivity removing a lot of noise and co-channel interference. It doesn't need a qualification in Advanced Plumbing to build it either!

http://www.crosscountrywireless.net/cardioid_loop_antenna.htm

Regards,

Chris
Hi Chris,

This is possible as well. With that said it seems like using 50 Ohm coax vs 75 Ohm is a more proper match here so we'll see what happens to performance. The SDRplay RSPdx is 50 ohm input. 

If for some reason it makes a big impact later on i can upgrade to better 50 Ohm coax :) 

Thanks 


Re: Tips to improve LAA+ Performance?

Martin - G8JNJ
 
Edited

Simon said

"The amp likes low inductance..

So bigger dia tubing the better (there is a point of low return though..ie dont be silly and use 3 inch tubing.)

To improve more then use 2 or 3 loops in parallel, spaced say 6inches apart."


Some notes on the subject here:-

https://www.g8jnj.net/loop-inductance

Regards,

Martin


Re: Tips to improve LAA+ Performance?

Chris Moulding
 

From the description of the extra noise on the coax cable mentioned earlier it may be caused by a poor shield connection between the coax cable and the connector.

This will allow the cable to act as an antenna picking up a lot of local RF noise while still appearing to work with the antenna or amplifier.

While we are talking about loops and their construction don't forget the cardioid loop design I recently posted. It's the one I'm now using as the reference antenna at the workshop due to it's directivity removing a lot of noise and co-channel interference. It doesn't need a qualification in Advanced Plumbing to build it either!

http://www.crosscountrywireless.net/cardioid_loop_antenna.htm

Regards,

Chris


Re: Tips to improve LAA+ Performance?

David Cutter
 

Eric

We are only interested in receive capability not transmit, so, cable loss is not so important, ie dB per m, etc.  It's most important to prevent ingress along the length of the feeder and shielded twisted pair is good at both electric and magnetic isolation, which is where the Cat5S comes in.  Nice to know it can also be cheaper.

David G3UNA

On 04 December 2020 at 08:28 Eric Inloes <compaq963@...> wrote:

[Edited Message Follows]
[Reason: I can't type while being half sleep wring these replies :) Sorry! ]

Hi David,

No, They weren't. It was 50 Feet of good quality RG-6 vs a short 3 feet run of RG-58. With that said on the SDRplay RSPdx at 15 Mhz the noise floor changed about 10 dBm higher for the 50 Ohm coax. That seems like quite a large difference which lead me to buy 50 FT of RG-58.

To me the higher noise floor could also mean more signal... Maybe not.

I know RG-58 isn't the best coax but i figure for the frequency range of LAA+ it's okay. RG-8X and LMR is far more costly.  

It was mentioned awhile go poorly mismatched to 50 Ohm could cause high noise and IMD products. Maybe the case here? 

Again, Sorry for the edits. Wish it didn't email you all. Trying to write this half asleep here :) 


Re: Tips to improve LAA+ Performance?

Eric Inloes
 
Edited

Hi David,

No, They weren't. It was 50 Feet of good quality RG-6 vs a short 3 feet run of RG-58. With that said on the SDRplay RSPdx at 15 Mhz the noise floor changed about 10 dBm higher for the 50 Ohm coax. That seems like quite a large difference which lead me to buy 50 FT of RG-58.

To me the higher noise floor could also mean more signal... Maybe not.

I know RG-58 isn't the best coax but i figure for the frequency range of LAA+ it's okay. RG-8X and LMR is far more costly.  

It was mentioned awhile go poorly mismatched to 50 Ohm could cause high noise and IMD products. Maybe the case here? 

Again, Sorry for the edits. Wish it didn't email you all. Trying to write this half asleep here :) 


Re: Tips to improve LAA+ Performance?

David Cutter
 

That's interesting. Are cables otherwise identical, eg single screen, diameter, manufacturer?

Chris has a good track record in using Cat 5(S?) cable which is excellent at keeping noise out.

David G3UNA

On 03 December 2020 at 18:40 Eric Inloes <compaq963@...> wrote:

[Edited Message Follows]

Hi All,

I like the multi loop idea. A bit interesting to say the least :) 

I guess we'll see with the 50 Ohm coax how it is and go form there. I did testing indoors between 50 and 75 ohm coax and it seems the noise floor changes quite a bit between them.

Thanks!


Re: Tips to improve LAA+ Performance?

Eric Inloes
 
Edited

Hi All,

I like the multi loop idea. A bit interesting to say the least :) 

I guess we'll see with the 50 Ohm coax how it is and go form there. I did testing indoors between 50 and 75 ohm coax and it seems the noise floor changes quite a bit between them.

Thanks!


Re: Tips to improve LAA+ Performance?

David Cutter
 

Hello Simon

Sturdy looking loops and it looks like you've put a lot of effort in to them.  

I was wondering how these would compare to Chris's idea of bicycle rims.  

David G3UNA

On 03 December 2020 at 16:46 Simon <ohhellnotagain@...> wrote:


The amp likes low inductance..

So bigger dia tubing the better (there is a point of low return though..ie dont be silly and use 3 inch tubing.)

To improve more then use 2 or 3 loops in parallel, spaced say 6inches apart.



Or even better use 4 crossed parallel loops..



To improve hf over lf use smaller dia loops..above pic shows loops of 80cm ( circa) squares..i have the preamp switchable directions, hence why 8 loops in pic.

Above works well from dc to 20mhz..

Simon g0zen




Re: Tips to improve LAA+ Performance?

Simon
 

The amp likes low inductance..

So bigger dia tubing the better (there is a point of low return though..ie dont be silly and use 3 inch tubing.)

To improve more then use 2 or 3 loops in parallel, spaced say 6inches apart.



Or even better use 4 crossed parallel loops..



To improve hf over lf use smaller dia loops..above pic shows loops of 80cm ( circa) squares..i have the preamp switchable directions, hence why 8 loops in pic.

Above works well from dc to 20mhz..

Simon g0zen


Re: Tips to improve LAA+ Performance?

leslie norton
 

Hi Eric

I can give you my experience with the LAA+ as initially i was disappointed.
Initially i used the wire that came with the LAA+ and quite near the house, supplied with bog standard RG58, then i used some screened sky type shotgun cable which is 75ohm.
performance improved, then i decided as i had bought a drum of the cable, to move it well away from the house by 70ft and put it on the shed, again an improvement (less noise)
The loop is only 2m up from the ground.

I then put my Airwave loop on that i was using with my Wellbrook ALA-100, a big improvement.

Now here is an interesting development, i used my SDRplay to supply 5v from its own supply and that worked but then i swapped that for the LAA+ own biasT with the DC socket on and supplied it with 13.8v that i supply my FTDX3000 transceiver with. I can now say that the set up i have equals my Wellbrook.

Note the shotgun cable i bought was a decent type and of course you have to split it, advantage is you now have double the length!!

Hope this helps.

I now use the LAA+ set up plugged into my Rx port on my FTDX3000 and if noise is high I Tx on my Halfwave end fed and Rx on my loop.

Les
G4JNW




On 3 Dec 2020, at 04:00, Eric Inloes <compaq963@...> wrote:

[Edited Message Follows]

So, I've had my LAA+ for awhile but initially HF performance above say 5 Mhz was pretty disappointing. Below that I was quite happy with it's performance.

With that said I'm back to the drawing board to try and improve it's performance. I've sense upgraded the loop form 10 feet of 1/4 inch copper pipe to 10 feet of 5/8 inch copper pipe bent into around a 1m loop to reduce the inductance. 

I was also using RG-6 75 Ohm coax and currently awaiting on some Amphenol RG-58 to switch to 50 Ohm and to try again. Figured RG-8X and LMR-240 isn't worth the cost for this. 

Any other ideas? :) 

Thanks


Re: Tips to improve LAA+ Performance?

Paul Newland
 

Hi Eric
From what experience that I've had, the LAA+ is a serious performer.
I have only used it with the associated base unit, which I'm sure works better than the Bias-T of my SDRplay RSPs and of course takes good care of frequencies below 500Khz.
I previously used athe forerunner of the LAA+, the HF/VHF version and the one before that.
I attached the HF/VHF version to a !M aperture loop,constructed of 15mm copper tubing and it worked well powered by a RSP BiasT above 500Khz and am still using it indoors attached to an aluminium bicycle wheel loop (handy at times).
Performance is AT LEAST comparable to my Wellbrook antenna and although I have now optimised my antenna for lower frequencies, it is also an excellent performer on the VHF airband ( although the loop is however centered only just over !M above ground level).
This experience has persuaded me that using the associated base unit is advantageous.
Best Wishes
Paul



Virus-free. www.avast.com


On Thu, 3 Dec 2020 at 03:10, Eric Inloes <compaq963@...> wrote:

[Edited Message Follows]

So, I've had my LAA+ for awhile but initially HF performance above say 5 Mhz was pretty disappointing. Below that I was quite happy with it's performance.

With that said I'm back to the drawing board to try and improve it's performance. I've sense upgraded the loop form 10 feet of 1/4 inch copper pipe to 10 feet of 5/8 inch copper pipe bent into around a 1m loop to reduce the inductance. 

I was also using RG-6 75 Ohm coax and currently awaiting on some Amphenol RG-58 to switch to 50 Ohm and to try again. Figured RG-8X and LMR-240 isn't worth the cost for this. 

Also I need to use the Bias-T for stuff below 500 KHz as the Bias-T with the SDRplay stuff will cut off anything below it. For that I decided to upgrade the PSU to one of these https://www.amazon.com/gp/product/B00B8860R0/ to avoid switching noise there. 

Any other ideas? :) 

Also, Sorry for all the edits!

Thanks


Tips to improve LAA+ Performance?

Eric Inloes
 
Edited

So, I've had my LAA+ for awhile but initially HF performance above say 5 Mhz was pretty disappointing. Below that I was quite happy with it's performance.

With that said I'm back to the drawing board to try and improve it's performance. I've sense upgraded the loop form 10 feet of 1/4 inch copper pipe to 10 feet of 5/8 inch copper pipe bent into around a 1m loop to reduce the inductance. 

I was also using RG-6 75 Ohm coax and currently awaiting on some Amphenol RG-58 to switch to 50 Ohm and to try again. Figured RG-8X and LMR-240 isn't worth the cost for this. 

Also I need to use the Bias-T for stuff below 500 KHz as the Bias-T with the SDRplay stuff will cut off anything below it. For that I decided to upgrade the PSU to one of these https://www.amazon.com/gp/product/B00B8860R0/ to avoid switching noise there. 

Any other ideas? :) 

Also, Sorry for all the edits!

Thanks


Re: Looking for UK source of low noise 5V DC supply

obrianboru@...
 

I have a clean 30 Amp 12 v shack psu but found that even short leads from it to bias tees, etc, were picking up rfi from nasty switch-mode PSUs in the house and shack.

I soldered small Belling-Lee filters at the point these leads enter the bias tees, amps, and other rf sensitive equipment and rfi has been cleaned up enormously.

Photo on my QRZ blog here: https://forums.qrz.com/index.php?threads/which-side-of-a-current-choke-needs-grounding-to-help-prevent-common-mode-or-rfi.700474/page-2

How they would cope with much stronger rfi on the power leads from a dodgy 5 v switch mode PSU, I don't know..... but it's worth a try.
73 Jeff


Re: Looking for UK source of low noise 5V DC supply

Keith
 

Thanks for the info Chris, that sounds just like what I am looking for and I will give it a try.
It will be much better than my current arrangement and at those prices you can't go wrong.

Keith


Re: Looking for UK source of low noise 5V DC supply

Chris Moulding
 

Due to EU regs for energy saving it is no longer possible to buy or sell a 5 V USB power supply.

There are some manufacturers who can still build a high quality switch mode power supply with good RF filtering.

For my own use to power antenna amplifiers and to replace all the cheap tat passed off as phone and tablet USB chargersI I've replaced them all with TT Electronics SW4479B 5 V 2.1 A USB chargers. This is designed for UK use with the 3 pin plug. It was originally designed to meet the high reliability (MTBF of 50000 hours) specification so it's a well made quality item. It appears to be RF quiet with no noticeable conducted RF on the mains supply or USB cable. If you put a receiver and antenna up against the charger there is some RF noise very close in within a few inches.

I bought mine from Rapid Electronics part number 85-2892, the current price is £6-89 + VAT.

TT Electronics probably make versions for other electrical supply sockets but I've not checked yet.

Regards,

Chris


Re: Looking for UK source of low noise 5V DC supply

David Cutter
 

I would be tempted to use a discrete regulator off your 12V supply, with suitable heatsink

David G3UNA

On 02 December 2020 at 11:12 Keith <groups.c6545e@...> wrote:

Hi, I know CCW do a low noise 12V power supply (which I have) but I am looking for a UK supplied 5V
version to run the USB port of the CCW LAA+ base amplified PCB.
Linear 5V supplies appear to be difficult to find at present in the UK.
Would also consider a variable voltage bench supply if that would work, but which one at a reasonable cost.
Anyone have any recommendations for this and where to get one from ?

Keith


Looking for UK source of low noise 5V DC supply

Keith
 

Hi, I know CCW do a low noise 12V power supply (which I have) but I am looking for a UK supplied 5V
version to run the USB port of the CCW LAA+ base amplified PCB.
Linear 5V supplies appear to be difficult to find at present in the UK.
Would also consider a variable voltage bench supply if that would work, but which one at a reasonable cost.
Anyone have any recommendations for this and where to get one from ?

Keith


Re: Loop height above gnd and 2 loops

Martin - G8JNJ
 

Hi Simon,

As you have effectively already got two identical loops mounted at 90 degees relative to each other, I think you should be able to steer the pattern simply by summing the two feeds and varying the amplitude between the loops. You may also need to provide a 0/180 degree phase flip to cover the full 360 degrees.

This has traditionally been done by feeding a Goniometer with the two signals, but I think you could just use two pots to do pretty much he same thing.

https://en.wikipedia.org/wiki/Bellini%E2%80%93Tosi_direction_finder

I originally thought that the Goniometer provides a phase variation as well as amplitude, but apart from a 0/180 degree phase flip when the moving and fixed coils cross their axis, this doesn't happen.

It simply relies upon the fact that the antennas are already in quadrature, so any angle or bearing can be synthesised by simply varying the amplitudes of the two signals relative to each other.

If you do wish to try varying both the amplitude and phase of the signals, then the simple circuit at the beginning of this document is a good start.

https://groups.io/g/loopantennas/files/WA1ION%20Phaser-everett-techcol%20dxm%20NHP.pdf

More notes on this page.

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

Regards,

Martin


Re: Loop above gnd.height vs take off angle

Simon
 

Hi Chris

Interesting..not concerned about hf..have fan dipoles for them and the existing loops.

Ok will give this a go tomorrow..( bigger loop on cardioid.)though it may well end up being square in shape as easier to make.

If you fancy sending me crt dia for the phaser please do..
I will keep it to myself..that I promise..if you dont fancy sending it I fully understand..

Currently building phaser using differential capacitor..thus eliminating the resistive lossy phase control..should also give full 360 degrees..The wa1ion ( might have got that wrong.) I recently built is too lossy, also relies on potentiometers which even though brand new are becoming tiresome..though it does work well better than the one i had before..( much better.)

Simon


Re: Loop above gnd.height vs take off angle

Chris Moulding
 

On 160m even with the smaller output from the cardioid loop the Loop Antenna Amplifier + will have enough gain. You could try increasing the loop size to 2m but you would loose performance at higher frequencies.

It would be a waste to use copper pipe for the cardioid loop, with the resistor wire works fine.

With a phasing unit if two loops are facing in the same direction (towards the USA in your case) they don't need to be inline or broadside as you can adjust the phasing between them for maximum gain. If they are not inline or broadside it may give a skewed pattern of nulls but this may be an advantage as you will be able to steer the nulls with the phasing unit at the expense of a dB or so of forward gain.

The original C and S Antennas cardioid loop array used four cardioid loops to give a very sharp forward pattern using separate coax phasing harnesses for inline or broadside operation.

I made a prototype phasing unit about two years ago and it was excellent at phasing two antennas especially nulling out noise or interference. We decided not to go ahead with it as it needed a lot of workshop assembly. I did get a lot of practice and experience of phasing antennas with it.

Regards,

Chris

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