G8JNJ

Hi Colin,

Good luck when trying to measure the IMD performance, especially using the single tone method.

Here are my measurement results, note that I'm using amateur grade kit to measure it, so there may well be errors creeping in, but I have spent more than 6 months gradually optimising the test setup, so that I can obtain repeatable results and at the very least 'compare like with like'.





Note that the calculated values using the two tone and single tone methods don't match, and the difference varies depending upon the amplifier configuration, so its not possible to apply a simple formula to bring them into agreement.

Wellbrook quote an OIP2 of +70dBm and an IOP3 of +40dBm for their 'old style' amplifier which the Wellgood is based upon, and an OIP2 of +90dBm and an IOP3 of +55dBm for their 'new style' amplifier.

My results indicate the Wellgood to be somewhere around an OIP2 of +57dBm and an IOP2 of +37dBm, which is not a million miles away but could be better.

It maybe that if I'd used slightly bigger ferrite cores and optimised the bias I could have matched Wellbrook's figures, or it could be that George has not quite got the transformer winding correct WRT the way the overwinds are placed on the binocular core with its three (possible) separate magnetic paths.

Bottom line the LZ1AQ is better than the old style Wellbrook, but the new style Wellbrook may be as good as, or better than, the LZ1AQ.

Regards,

Martin - G8JNJ

@ Kovalr

Yes, some time ago I asked Kari if he could include the ability to map GPIO ports to specific antennas so that it would be easier to accommodate binary switching of banks of relays as you have done. Unfortunately he hasn't so far) been able to do this.

You have two (or maybe more) options. You could modify Kiri's code to switch more than one GPIO pin at a time when an antenna is selected, or alternatively use some diodes to provide simple logic to 'steer' switching signals from each GPIO output to drive one or more relays at a time or as otherwise required.

I use the second method, as I'm not really a software guy and diodes are cheap.

Regards,

Martin - G8JNJ

https://github.com/OH1KK/KiwiSDR-antenna-switch-extension


https://github.com/OH1KK/KiwiSDR-antenna-switch-extension/blob/master/docs/ant-switch-backend-beagle-gpio.txt

This extension uses Beagle GPIO pins

P8 pin 11 - GPIO_45 - Antenna 1
P8 pin 12 - GPIO_44 - Antenna 2
P8 pin 13 - GPIO_23 - Antenna 3
P8 pin 14 - GPIO_26 - Antenna 4
P8 pin 15 - GPIO_47 - Antenna 5
P8 pin 16 - GPIO_46 - Antenna 6
P8 pin 17 - GPIO_27 - Antenna 7
P8 pin 18 - GPIO_65 - Antenna 8 (not available in webui yet)
P8 pin 19 - GPIO_22 - Antenna 9 (not available in webui yet)
P8 pin 26 - GPIO_61 - Antenna 10 (not available in webui yet)

When you install the extension it will ask you which interface you wish to use.

Regards,

Martin - G8JNJ

Hi Paul,

You can also trade the overall notch depth against the notch bandwidth by varying the L/C ratio.

In most cases you don't need to have more than 10 to 20dB notch depth in order to bring the worst offenders down to an acceptable level.

Here's a couple of filters I made using SMD parts. If you remove the 5.6R resistors and are using components with a good value of Q (L >40)
you can obtain >20dB notch depth.




This is the frequency response with the resistors fitted.



Regards,

Martin -G8JNJ

Hi John,

Great, thanks for considering the comments, I look forward to trying them out :-)

Regards,

Martin - G8JNJ