... Subject: Re: [softrock40] Re: FT990 and Softrock ... I have been investigating the use of the 47.05MHz IF of my FT840 with Softrocks. For testing purposes
Message 1 of 1
, May 1, 2013
----- Original Message -----
Subject: Re: [softrock40] Re: FT990 and Softrock
> Adam Jacobs and I are working together on a project where Adam is going
> to evaluate a special IF version of the RX Ensemble II receiver. The
> Ensemble II IF test unit has been built and was mailed to Adam
> The Ensemble II IF test unit is setup to cover most popular IF
> frequencies with band coverage including 400 kHz - 800 kHz, 4 MHz to 16
> MHz and 40MHz-50MHz. The 40MHz-50MHz coverage is by 1/3 sub-harmonic
> sampling and there is some concern about that range having enough
> sensitivity for the IF application.
I have been investigating the use of the 47.05MHz IF of my FT840 with Softrocks.
For testing purposes I decided take the IF from the roofing filter input with 5pF to a JFET source follower. High input impedance,
low output impedance.
The output from this was sufficient to satisfactorily drive my FT847 tuned to 47.05MHz.
However both Softrocks I tried using subharmonic mixing were not sensitive enough, a 20dB mmic amplifier rectified that with maybe
I used a BPF as described here <http://groups.yahoo.com/group/softrock40/message/27700> with the Si570 at 15.697x4MHz.
This puts the "theoretical LO" about 20KHz outside the roofing filter's passband but I've done no real checks to see if this
the FT840's performance. Probably it would be best to use something like the Z10000 buffer.
But this raises an interesting point. With subharmonic mixing the 47.05MHz centre frequency is not actually present. There is no
signal to feed back into the rig's IF.
I did further checks and can find no sign of any interaction.
So, would using subharmonic mixing on different IF panadapter applications remove worries about signals close to an IF feeding back
into the rig? Even when subharmonic mixing is not needed?
It does seem that I can use a small offset so that a more equal range each side of the tuned frequency my be seen.
73 Alan G4ZFQ
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