or other shortwave receivers

my goal for this work:

  In april 2014 in the german magazine "FUNKAMATEUR" was published an article from
DC8RI for nice receive converters in 3 versions for 6m, 4m and 2m.
In april 2015 the converters can be found as KIT in the "FUNKAMATEUR online shop".
  I decided to buy the 4m-version. An analysis of the circuit showed me that it must be possible
to modify the circuit to make a  combined 4m and 6m receive converter 
for the use with my SDR-IQ  which has a RX range from 0-30MHz.
So it will also work with other shortwave receivers.

I decided to use an LO frequency of 42MHz. This LO frequency is
also availiable in the shop. This gives me the possibility to use both bands
with the SDR-IQ without band switching.

The 6m Band 50-52 MHz can be received from 8-10 MHz.

The 4m Band 70-72 MHz can be received from 28-30 MHz.

To  get the needed receiving performance and selectivity the filters
of the converter have to be modified.
So I started my work with the "Elsie Filter Designer".

For the input bandpass filter I used the following components:
The simulation gave the following results.
input bp sim
The main bandpass modification looks like this.
main bp
and the simulation results of the main bandpass filter
main bp sim
and finally the LO filter must be modified ....
lo filter
and the simulation with a deep pole on 84MHz (1st LO harmonic).
lo filter sim
The modified circuits and components can now be seen on the PCB.
Note: change C7,C13 and C13 also to a bigger value... i used 1.5nF

Measurement results:

After all modifications I got the following measurement results with an RF input power of -50dBm.

receive frequency (-50dBm)
if frequency
image rejection
50 MHz
8 MHz
23 dB
60 MHz
18 MHz
-30 dBm
20 dB
70 MHZ
-26 dBm
24 dB
34 MHz (image frequency)
8 MHz
-78 dBm
-28 dB
51 dB
24 MHz (image frequency)
18 MHz
-90 dBm
-40 dB
60 dB
14 MHz (image frequency)
28 MHz
-102 dBm
-52 dB
76 dB

After a first "real world" test all is working well. 

If you need more information please write an email


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  last change: 11.june 2015 (DG0OPK)