[hpsdr] Toroid evaluation for filters, transformers, IIP3

[Glenn]

Dear all

Please evaluate the possible filter toroid possibities explored here:

Frontend - Filters
Band-pass filters, first attempt:
http://www.xs4all.nl/~martein/pa3ake/hmode/bpf_intro.html
Quote: "...
After the disappointing results when I measured the initial BPF's, 
they were readied long before I could reliably measure IP3, it was 
clear that serious improvement was needed to have the BPF's not 
effect the frontend's IP3 too much. On some bands like 40M, +50dBm 
IIP3 or better is needed!
...
The voltage over the inductor should be kept as low as possible. This 
means that the loaded Q of the filter should be kept low. Therefore 
the bandwidth of the BPF should be made as wide as is acceptable. 
There is obviously a trade off here.
...
Bigger toroids with a larger diameter are needed.
..."

http://www.xs4all.nl/~martein/pa3ake/hmode/frontend_intro.html
Quote: "...
Especially the T50 toroid based input band pass filters I used were a 
problem. They would not allow the frontend's intercept point to 
exceed +40dBm. But also the quartz roofing filter was limiting the 
overall IP3 at +42dBm. The overall result of this combo was that the 
IP3 was in the upper thirties, which is good by all means, but the 
mixer could do much better, potentially over +50dBm on 40M...
..."

http://www.xs4all.nl/~martein/pa3ake/hmode/conclusion.html
Quote: "...
The best values are found on the bands where it is needed most namely 
80M and 40M. Those values are easily exceeding +46dBm making it very 
difficult to construct the surrounding subsystems (BPF and roofing 
filter) so that they don't compromise the mixer's IP3.
...
I find it quite amazing that on 40M toroids with a size usually used 
in 100W PEP transmitter output LPF's are required to remove the IP3 
bottleneck in the receiver.
..."


Main page:
http://www.xs4all.nl/~martein/pa3ake/hmode/
http://www.xs4all.nl/~martein/pa3ake/hmode/introduction.html


IP3 measurement
Signal Generators and Hybrid Combiner:
http://www.xs4all.nl/~martein/pa3ake/hmode/ip3measurements.html

kind regards,

Glenn/OZ1HFT