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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


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


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


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


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




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!


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!


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 :) 


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 :) 


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


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


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 


Tom Crosbie G6PZZ
 

FWIW, I prefer UR43. It has less loss (a gnat’s whisker) and better screening than RG58 and I’ve been buying it from Henry Westlake for almost 40 years.

 

Tom G6PZZ

 

 

From: CrossCountryWireless@groups.io <CrossCountryWireless@groups.io> On Behalf Of Eric Inloes
Sent: 04 December 2020 08:29
To: CrossCountryWireless@groups.io
Subject: Re: [CrossCountryWireless] Tips to improve LAA+ Performance?

 

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 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 high noise floor could also mean more signal...

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? 


Eric Inloes
 

Hi all,

RG-58 is finally here and it appears that all the tweaks have improved HF somewhat.

HF conditions are poor now so i'll have to do some more testing.


Jon Hall
 

Only had my LAA+ for a short time .

Before that started with a mla30 - that got me started on a loop.
Initially 'ok' results ... but have now replaced the wire loop with some stainless steel strap that was hanging in the shed.
Pleased with the results - only in the loft space - but luckily we're on a farm so not much noise here.
Its all connected to an sdrplay/uno
All good fun in these lock-down times.

atb Jon G0MYW


Simon
 

Hi

your on a farm?!!

beverages..endfire cardioid loops ..soo much space!!

get your loop out  into a field away from your house would be the first thing to do..(20m?) 

wow a farm..no noise..you sooooo lucky..

simon