HL2 below 2 MHz

[Heikki Ahola]

Hi group, 

I am considering to use my HL2 for receiving below 2 MHz. It seems to me that T2 is the limiting factor and in the schematic there is an option of hand winding another transformer on BN 43-2402 for replacement. In addition, some higher permeability material, like 73, has been suggested for T2. I wonder is the two transformers could be paralleled, i.e. to make an insert and plug it on top of the existing T2 in the HL2 board ?  Another possibility is to make an upconverter with DBM, my extended build (see the Gallery !) could easily accommodate such an addition !

73 de Heikki (OH2LZI)

[in3otd]

Hello Heikki,
how low do you need to go? Using a BN43-2402 as described here should be good to 100 kHz, using a BN73 core will probably allow to go even lower and still cover the upper HF. Simply paralleling two transformer will not work, as the one with the lower inductance will shunt the input - you may need to build a diplexer to feed both but it seems easier to me just to build one proper transformer, hi.

73 de Claudio, IN3OTD / DK1CG

[Heikki Ahola]

Hi Claudio,

Tnx, 100 kHz sounds OK ! This means that just replacing the existing SMD transformer with BN43-2402 would do the job ! If needed, I would experiment with 73 material ...

73 de Heikki (OH2LZI) 

[in3otd]

Hello Heikki,
out of curiosity I did some measurements on a few transformers that can be used for T2 on the H-L; the graph below show the transformer response for
- BN43-2402 with 14 turns : 5 turns
- BN73-2402 with 14 turns : 5 turns

- MACOM MABA-010143-FLUX18 (the default transformer in the BOM)

using the BN43 core the response is about 3 dB down at 100 kHz, while with a BN73 core it works nicely from well below 100 kHz to 30 MHz and beyond

73 de Claudio, IN3OTD / DK1CG

[Heikki Ahola]

Tnx Claudio,

It seems, after all, that 73-material is the right choice for my application, need only to find the core somewhere as my junkbox has none currently !

73 de Heikki (OH2LZI)