LAA++ is generating/receiving harmonics


Juan - EA5XQ
 

Hi,

Just today testing of LAA++ I have observed (compared to a End Fed or MiniWhip) that I am receiving a lot of harmonics in all bands. I have tested it with AirSpyHf+ and IC756 and surprisingly, for instance, in 5785Khz I am receiving dozens of harmonics.

Could it be the LAA++ damaged?


Simon
 

What size loop are you using with it??

Simon


Juan - EA5XQ
 

Loop made of Copper, 1.2 m diameter


Juan - EA5XQ
 

Just to compare

2_endfed.png: Signal with Endfed
3_direct-loop: SIgnal with the Loop

I added also a strange behaviour. With the LAA++ T-bias, if I put the power jack (13.8V) ’til the end of the female conector I get much more interefences (5_connector_full). 

This is the first time that this happens to me ... it make useless the Loop. 


Chris Moulding
 

Hi Juan,

Thanks for sending the screen shots.

It looks like the amplifier is faulty.

I'm building a new batch I can ship a replacement in a few days if you wish.

Regards,

Chris


Juan - EA5XQ
 

Hi Chris,

Which could be the reason? This is the last amplifier that I got from you (you sent it to my son in Edimburgh) and it has been working fine so far. 

I will appreciate if you could send me a replacement. Thanks

regards


Chris Moulding
 

The fault could be caused in several ways.

The first thing to check is that the connections between your loop and the amplifier are secure.

A high resistance connection especially with copper pipe can act as a diode if there is any corrosion on the copper joint connection.

A high resistance in the coax connections can also cause this due to the high resistance limiting the current flowing to the amplifier.

Other possible causes for the fault are a fault in the bias circuit or the amplifier device is damaged in some way and is about to fail.

Regards,

Chris


Juan - EA5XQ
 

Currently I am using a coax direct from bias-T ’til the amplifier. I will check the quality of the BNC connectors but it goes directly, no copper pipe or similar.

I tested with other Bias-T and the results were the same.

This aftternoon I will be making more tests


Juan - EA5XQ
 

It seems that the problem could come from the Bias-T when feeding it. If the power connector coming from your original PSU is introduced fully it provokes what you see in the second picture. 


h. garcia
 

Juan, out of curiosity: what happens if you connect the coaxial directly to the receiver, with no Bias-T and nothing powering the loop?

Do you still see signal on the band with fairly good signals?



On Mon, Apr 25, 2022, 20:20 Juan - EA5XQ <juan@...> wrote:
It seems that the problem could come from the Bias-T when feeding it. If the power connector coming from your original PSU is introduced fully it provokes what you see in the second picture. 


Martin - G8JNJ
 

On Wed, Apr 27, 2022 at 06:18 AM, h. garcia wrote:
Juan, out of curiosity: what happens if you connect the coaxial directly to the receiver, with no Bias-T and nothing powering the loop?
 
Do you still see signal on the band with fairly good signals?
As a further test, turn off your mains AC to DC power supply and try using a 12v battery to power the loop instead.

This removes any noise that may be generated by your power supply and conducted along the DC cable, plus it also removes any 'ground' loop problems that may exist.

Regards,

Martin


Juan - EA5XQ
 

Apologies for the delay, the answer is yes, indeed. I find signal on the band although with low level signal. I have discovered that most likely BiasT is faulty

I was using another BiasT (not the original) and it seems that works. It is strange because the faulty one works fairly well unless you push the connector ’til the end (as it should be). If you connect the power jack from PSU just slightly it works.

I will see how to get a new BiasT from Chris.

Thanks all for the support