Original Message -----
Subject: [softrock40] Re: Crystals in Softrock LTE combined kit
Many thanks for discussing this issue. From my egoistic point of view, using this ¡°sub-harmonic¡± mode has not only a financial advantage. I¡¯ve remarked that spurious trying to "escape" from the receiver -antenna circuit- on the fundamental frequency (I mean the Xtal/4 when using tayloe mixer the ¡°traditional¡± way) are less important when using a sub-harmonic mode. That¡¯s an important point when you are dealing with the high amplification levels of an I.F., even if you are using a high isolation coupler to pickup the signal. The softrock ¨Cand other direct conversion SDR using digital mixing devices- are definitely not ¡°clean¡±.
Have your measured the same results on your rigs ?
The reason of my interest of this subject is that I¡¯m trying to modify an almost conventional superhet transceiver, and I¡¯m wondering if putting an xtal driven Softrock in the IF (for receiving AND transmitting) would¡¯nt be a nice solution. This would addd new modulation schemes (FM, psk, rtty etc¡ ) to a ¡°SSB/CW only¡± rig in RX and in TX. This approach would also give the ability to offer a free (as in beer) bandscope/spectrum-waterfall display to a analog transceiver. Nothing new in fact.
I wonder if it would be smart to use the so called ¡°subharmonic¡± mode during receiving, and working on the fundamental during transmission (just switching the active xtal with a TX/RX signal, or changing a Si570 I2C word to do the same thing). A kind of ¡°6.2 Lite¡± working in duplex mode for 10.7 or 9 MHz in other words.
Marc,
I have used this technique for a pandaptor at 47.05MHz
As you say, there is no LO in the middle. But surely in the normal mode Softrocks this can be sufficiently reduced, the Z1000 (is that right?) has very good isolation.
I'm not sure about any RX/TX combination. You have to interface a digital program with the radio, be it SDR or conventional.
Most digimodes use SSB, unless you really want FM modulation is there really any point in making it more complicated?
73 Alan G4ZFQ
