Date   

Getting started...

Alan Clark
 

Hi everyone. 

Just over a year ago, I bought a second-hand device on Ebay, which is labelled SDR-4+ HF/VHF receiver. It has a number on the side, which is 0350. All the seals seem intact. 

I'm one of those people who took up SDR/SWL as a hobby and started with the RTL-SDR and eventually bought a number of Airspy and SDRPlay devices. 

I followed whatever guidance I could find online to install this SDR-4+ and it always seemed to me that somehow the driver was not working properly. I could hear signals, but could not seem to tune it properly. In the end, I gave up and put it to one side. Now, I have an entirely new PC and I'd like to try once again to get it working. I am using Windows 10, x64 bit, with a good graphics card. I have installed HDSDR and it's working with an Airspy Discovery. I'm not so familiar with this software, preferring SDRSharp and SDR Console. 

Could someone please point me in the direction of up-do-date drivers and let me know if there is a recent online guide on how to get this thing going. 

I have one basic question. The device came with two short USB cables, with USB 'B' connectors for the device itself. I am using USB 'B' cables for other devices and I've found it convenient to use cables which are 2 and 3 metres long, so that devices can be located further from the PC and monitor, which, I'm sure you all know, are sources of a lot of RF noise. Can I expect that 2 and 3 metre cables will work OK with this device?

Many thanks

Best wishes
Alan Clark 



Loop Types

Keith Ballinger G0RQQ / VA2QU
 

I am considering the CCW VLF loop amplifier for monitoring LW and MW broadcast stations as well as the 472kHz and 136kHz amateur bands plus NDB beacons. This will complement my home-brew Wellbrook clone for HF.

However, I am a little baffled by the apparent choices for the actual loop itself. I have seen designs using a single turn of wire or metal strip, single turns of coax cable, single turns of coax with a short section of braid removed opposite the feed-point, double turns of coax, and Moebius loops (a single turn of coax with the centre conductor and braid transposed opposite the feed point).

Can anyone suggest where I can find more info on the advantages/disadvantages of each type, or alternatively suggest which would be the best for my application?

Regards,
Keith


Re: LAA+ Surprisingly good at VHF

Chris Moulding
 

Hi Paul,

Thanks for the feedback on your experiments at VHF with the Loop Antenna Amplifier +.

We specify the LAA+ to cover up to 150 MHz due to the low pass filter built into the head unit. In practice it will cover the marine band around 156 MHz with a few dB of loss.

There are two ways that you can improve reception of the VHF marine band with the LAA+.

The first is to check the polarisation of your loop. If the LAA+ is at the bottom of your loop then its horizontally polarised at VHF. For vertical polarisation you need to feed the loop from the side.

The second point is that at VHF the loop is acting as a full wave loop like a quad element. If you make the loop out of wire 1963 mm or 77 inches long it will be resonant on the VHF marine band.

If you try both these changes I'm sure that the loop antenna will out-perform your discone.

Regards,

Chris


LAA+ Surprisingly good at VHF

Paul Sayer
 

Because I can I decided to see how the LAA+ performed at VHF when compared to a VHF/UHF discone. 

My set up is an RSP2 connected to a discone at about 4m AGL. CCW loop about 1m AGL. RSP1A is connected to to the loop. I am by the sea in Kent with a clear view out to sea. I am at a static caravan, so the loop is surrounded by lots of metal boxes. Testing by listening to marine VHF. Coax similar type and a similar length

Expectation - Hear nothing using the loop

Result  - Hearing quite a lot.

Very surprised considering where the loop is mounted. 

Yes, signals are down on the loop and SNR is worse. I can't at the moment get the loop higher. Due to the generally short transmissions I haven't checked the loop pattern and nulls. The attached screenshot shows a Dover Coastguard broadcast. Left screen is the loop and the right is the discone.  I think the Tx is very close to me but don't know where.

Conclusion - Very surprised at the result as my expectations were low. More testing needed.

Paul G0VKT


Re: Loop antenna removal

Tom Crosbie G6PZZ
 

Keep that file handy Chris, I expect to be in a similar situation in the next 12 months. I’ll be starting from scratch, looking for permission to instal something.

 

Tom G6PZZ

 

From: CrossCountryWireless@groups.io <CrossCountryWireless@groups.io> On Behalf Of Chris Moulding
Sent: 30 July 2020 16:06
To: CrossCountryWireless@groups.io
Subject: Re: [CrossCountryWireless] Loop antenna removal

 

Hi Gordon,

Sorry to hear about your brush with officialdom. I have a relative who lives in a retirement flat and it's the same for her. Anything out of the ordinary or not easily understood is not tolerated.

I can send you a letter or an email explaining what a loop antenna is and how it works in Health and Safety terms.

What's best for you and email of a letter sent via the post?

For extra detail what type of receiver are you using?

Regards,

Chris


Re: Tips to improve LAA+ Performance?

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? 


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

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