...I looked at what the key difference if between the Elektor board and all others (QRP, Softrock, etc). Amongst many things, it is the main multiplexer chip, the Elektor board uses a HC4066 and the spec sheets state the max switching frequency of that chip is around 30 - 35Mhz. On the other hand, the other boards use the 3253 chip which can switch at approx 250Mhz (although the si5351 could not go that high). So, maybe the Elektor board is beyond it's capabilities to receive proper WFM. My question is: is there a success story here with the Elektor board and WFM reception ?
Hi Les,
change the 74HC4066 to a better 74LVC4066.
The 350MHz of the 3253 is the max. high-pass frequency of the switches and not the switching frequency. The max. switching frequency is about 100Mhz. The 74LVC4066 has the same max. switching frequency and a the switches a bandwide of max. 250MHz@5V.
The max. output frequency of the 5351 is about 300MHz, so that you must change the johnson counter for 2xfo and not 4xfo frequencies. To do this, clock the both D-FF separate with 180° phase shiftet 2xfo clocks from two outputs of the 5351.
Karlchen