LAA++ Questions, Transmitting and Raspberry Pi #raspberrypi


Jack
 

I recently received my LAA++ (one of the new ones with the bias t in a box). I put my wire inside a 15mm JG Speedfit plastic pipe, connected it together and it all seems to work. Amazing.

I am operating it in split mode with VirtualHere running on my Pi 4, connected to SDRPlay’s SDRdx, inside my garage and SDRPlay’s SDRuno on my Windows machine in my office.

I am brand new to this amateur radio stuff so I have some questions:

  • Can I use the LAA++ for transmission?
  • What is the head unit (the one directly connected to the wire antenna) actually doing? Amplifying the signal, matching the impedance, something else?
  • I read about magnetic loop antennas, can the LAA++ do this, is it worth it?
  • Can the LAA++ be used with other antenna configurations (delta, dipole, L, etc)?
  • Is it possible to transmit the LAA++ directly from the Pi (apparently the Pi can transmit about 10mW but needs a filter as, for WSPR as an example, it’s transmitting a square wave)?

 

Jack, M7EAS


Simon
 


Hi Jack..


First welcome to ham radio!


2nd been a ham for 40 yrs now ..the more I learn the more I realise i know nothing!! 


So to answer your questions..see below



I recently received my LAA++ (one of the new ones with the bias t in a box). I put my wire inside a 15mm JG Speedfit plastic pipe, connected it together and it all seems to work. Amazing.

I am operating it in split mode with VirtualHere running on my Pi 4, connected to SDRPlay’s SDRdx, inside my garage and SDRPlay’s SDRuno on my Windows machine in my office.

I am brand new to this amateur radio stuff so I have some questions:

  • Can I use the LAA++ for transmission?
NO NO NO!
  • What is the head unit (the one directly connected to the wire antenna) actually doing? Amplifying the signal, matching the impedance, something else?
Matching and amplifier of small signal from loop
  • I read about magnetic loop antennas, can the LAA++ do this, is it worth it?
Mag loops can and do perform brilliantly if well made.. but nothing really to do with the laa.
  • Can the LAA++ be used with other antenna configurations (delta, dipole, L, etc)?
Not without modding.. it’s designed for small rx non tuned broadband loops.
  • Is it possible to transmit the LAA++ directly from the Pi (apparently the Pi can transmit about 10mW but needs a filter as, for WSPR as an example, it’s transmitting a square wave)?
See first question NO NO NO 

Regards Simon g0zen ( mag loop Simon.) 

 

Jack, M7EAS


Chris Moulding
 

Hello Jack,

Good to hear that your loop and the LAA++ is working OK.

Answers to your questions:

The LAA++ is for receive use only.

The head unit contains an amplifier and other circuitry to isolate the loop from the amplifier and a common mode choke to isolate the amplifier from the coax cable so that RF signals and noise don't get into the loop.

When a loop is used with a LAA++ it acts as an aperiodic loop, in other words it is untuned and wideband and the amplifier amplifies the very weak signal induced into the loop by the electromagnetic field.

A magnetic loop antenna is usually a tuned loop where the inductance of the loop is tuned in a resonant circuit with a capacitor. To get a reasonable efficiency the loop has to be made out of thick copper pipe or similar.  The badwidth, if efficient, is very narrow typically 7-10 kHz at 14 MHz. The problem with a magnetic loop antenna is that even at low power the voltage and current flowing in the loop are very high. The magnetic and electric fields are also dangerously high close into the loop.

A few years back we investigated making a prototype HF magnetic loop for the amateur radio market but came to the conclusion that they are not safe. We decided not to sell them. Others may tell you different, maybe their antennas are lossy and don't generate the high electric and magnetic fields.

 Many different loop configurations can be used with the LAA++.. Welcome to your new hobby making loop antennas!

It isn't possible to transmit into the LAA++. It's a receive only antenna and it would damage the amplifier.

Regards,

Chris


Jack
 

Thank you both for your replies.

I do believe that this is the perfect first antenna for me - one that will keep me occupied.  I have also seen this dinky transmit antenna that will also keep me occupied (https://k6ark.com/kitsandparts/).

Where might I find ideas for potential LAA++ loops?

Jack


Simon
 

Jack

Re tx antennas..

Where do you live?
Do you have a garden? How big?

Cos it is REAL easy to make a dipole for frequency x that will work well on tx if you have some space..

Ie all you need for 14mhz (20m) is 10m at most..at a height of 10m if possible( but lower will work.) it could be in an inverted V , less space needed then ..

It will make the “ anteena” you showed look rather poor.

Just saying..feel free to ask..Simon

And yes Chris is correct about possible issues with mag loop antennas. Best avoid untill have some experience, but if you have a sensible garden then antenna “world” is easy..( assuming nice neighbours and loving Wife!)


Jack
 

Thanks again Simon. The dinky antenna is interesting for mobile use (I sail on other people’s boats, and love hill walking).

My back garden is about 40m long and 6m wide, my house is about 7.5m tall and my front garden is another 6m. 
For a whole bunch of reasons (including neighbours) I don’t want a tall antenna or supporting mast.

Given my preliminary research, I will definitely be using a dipole. I am interested in digital radio (e.g. FT8 and WSPR) and, from what I have seen, there is a lot of activity on the 80m, 40m, 20m and 10m bands. 1/4 wave dipole for 80m would be 40m in length, right? Worst case, I run several dipoles from the same supports.

The bad news is that I live in North London so I cannot avoid RFI: my noise floor isn’t going to be low. The good news is that digital radio is better able to deal with that.

One of my other passions is space and it seems like using satellites for radio can be done almost anywhere. So I will eventually look into that too!




Paul Sayer
 

Use the loop for receive and another antenna for transmit. It's what I do and it lowers the noise floor a lot. 

Paul
G0VKT 

On Wed, 16 Mar 2022, 09:12 , <jack@...> wrote:

Thanks again Simon. The dinky antenna is interesting for mobile use (I sail on other people’s boats, and love hill walking).

My back garden is about 40m long and 6m wide, my house is about 7.5m tall and my front garden is another 6m. 
For a whole bunch of reasons (including neighbours) I don’t want a tall antenna or supporting mast.

Given my preliminary research, I will definitely be using a dipole. I am interested in digital radio (e.g. FT8 and WSPR) and, from what I have seen, there is a lot of activity on the 80m, 40m, 20m and 10m bands. 1/4 wave dipole for 80m would be 40m in length, right? Worst case, I run several dipoles from the same supports.

The bad news is that I live in North London so I cannot avoid RFI: my noise floor isn’t going to be low. The good news is that digital radio is better able to deal with that.

One of my other passions is space and it seems like using satellites for radio can be done almost anywhere. So I will eventually look into that too!




Robin Maddison
 

G5RV 102ft😁

Robin 
GØGNE

On 16 Mar 2022, at 10:13, Paul Sayer <paulsayer123@...> wrote:


Use the loop for receive and another antenna for transmit. It's what I do and it lowers the noise floor a lot. 

Paul
G0VKT 

On Wed, 16 Mar 2022, 09:12 , <jack@...> wrote:

Thanks again Simon. The dinky antenna is interesting for mobile use (I sail on other people’s boats, and love hill walking).

My back garden is about 40m long and 6m wide, my house is about 7.5m tall and my front garden is another 6m. 
For a whole bunch of reasons (including neighbours) I don’t want a tall antenna or supporting mast.

Given my preliminary research, I will definitely be using a dipole. I am interested in digital radio (e.g. FT8 and WSPR) and, from what I have seen, there is a lot of activity on the 80m, 40m, 20m and 10m bands. 1/4 wave dipole for 80m would be 40m in length, right? Worst case, I run several dipoles from the same supports.

The bad news is that I live in North London so I cannot avoid RFI: my noise floor isn’t going to be low. The good news is that digital radio is better able to deal with that.

One of my other passions is space and it seems like using satellites for radio can be done almost anywhere. So I will eventually look into that too!