[CQ-Contest] Two Radios, one band

George w2vjn at rosenet.net
Sun Jun 21 16:59:21 EDT 1998

K4OJ wrote:

>Other ideas on two rigs one band?

>...I do not think that filtering enters in here due to the small
>differences in frequency....is there something other than antenna
>separation which can help?

LC filters are not much help when operating in a single sub-band due to the
small percentage frequency differences.  However, it is no problem for
crystal filters.  They can be inserted in the receiver input line and will
provide high attenuation to signals out of the passband.  Such filters will
be available from International Radio in mid August.  The initial offerings
will be for the low ends of 40 and 20 meters.  Specifications are as

          Pass band, 1dB       Stop band, 60 dB

          7000-7015 kHz            +/-22.5 kHz                 

          14000-14020 kHz         +/-30 kHz 

For both units the impedance is 50 ohms and the loss is 4 dB max.  If there
is sufficient interest, filters can be made for any frequency in the 80
through 10 meter bands.  When the filters are in hand, I'll make complete
lab measurements on them available including intermodulation test results.

It should also be noted that under certain conditions, phasing techniques
can be utilized to null out the transmitted signal in a separate receiver. 
If this is done correctly, the wide band transmitted noise can also be

To be truly effective, some combination of all the suggested methods may be

w2vjn at rosenet.net                 

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