In recent years a bread of radio using the technology known to as "direct RF sampling", to form a SDR radio, have emerged as todays radio technology. But however, what is direct RF sampling.
Ham's may perhaps be aware of the SDR Intermediate stage decoding of radio signal using SDR technologies. This principle uses mathematics to unwind the analogue signal into digital numbers, using an Analogue to Digital convertor, and from this using mathematics sums within a computer programme, then reproduce the voice audio, or even the CW signal or data message.
The direct RF sampling is principle as I understand things, the same digital SDR "I.F." decoder, instead of remaining tuned to say 9MHz, the digital "I.F." is retuned to cover the short wave spectrum from say 100KHz up to say 25MHz, with signal directly from the antenna input via a booster amplifier ( 1uV to say 1mV ), as with the Icom IC705 radio. It seems that after this point, the IC705 then uses an RF down convertor, from the antenna signal ( 25MHz and above ) to a usual "I.F." frequency, say 9MHz.
I do not known if the front filter after the antenna connection is tunabel, as with a LC tuned radio front end as in the old days, if not, then a LC tuneable circuit may perhaps be usefull. The front end tuned circuit, is usually tuned with a banked variable capacitor, the circuit was deisgned to tune both the front end circuit, as well as the local oscilator circuit. Today, these LC tuned front end circuits, are referred to as a Pre-selector circuit. The old valve, or vacuum tube radios, use pre-selector circuits.
A pre-selector circuit is not new technology, despite the recent high end radio brouchors.
Using a front end tuned circuit, even if the manufactures tuned the front end parallel circuit varicap doide with a digital to analogue convertor, with data from the micro-controller, tuning the radio, would go along way to close the front end bandwidth to around 500KHz or less, to say 100KHz with multiple stage bandpass tuned circuit filters.
Or may be, make ones own pre-selector, by adopting the LC ratios of the denco coils RF circuits.
Now I have an idea. As the Icom IC705 has a parametric display, the ic705 could be used as sub-section unit for a microwave transvertor.
Normally the radio used would be perhaps a 70cm radio as the "I.F." tx/rx unit, but the ic705 has the added advantage of the parametric disply, which is essentially a spectrum analyser display.
I am not sure if the ic705 has an external ptt line output, so the tx/rx circuits of the microwave transvertor could be switched, but an additonal interface lead between the microphone and the ic705 radio, would then provide the external ptt output interface control for the transvertor.
The next thing, if the ic705 is connected to a 3cm transvertor, while on the 430MHz, could the ic705 display then show 10,300MHz thus the ic705 showing the operational frequency on the transvertor antenna connection.
If on the 6cm band, the ic705 made to show on its lcd display say 5,760MHz, which is within the narrow band section of the 6cm band. The narrow band section is from "5.755MHz to 5,765MHz" then the ic705 actually operating between 430MHz to 440MHz, while showing from "5.755MHz to 5,765MHz" on the ic705 lcd display, operating on the 6cm band while using the 6cm to 70cm transvertor.