Most of the time when an Owner purchases a non-SDR commercial radio, the last thing to be considered is how many conversions are involved.
The quick look criteria for the purchaser is how does it sound, the power output, how many bells and whistles are included and if it is the most popular.
Everyone knows you are judged by the radio you are using. The more expensive the radio the more status you have in the greater ham community. Sadly, when you announce you are using a homebrew radio, the comment that follows: "Well it sounds OK for a homebrew radio".
But for the homebrewer the choice of single, dual or multiple conversion suddenly becomes the burning question of the day. Quite obviously a single conversion likely involves less circuitry which translates into less cost. The less circuitry approach also sidesteps the issue of unwanted mixing products and at times can drive some innovative solutions.
At this point proponents of single versus dual conversion are on par with our current political environment as to mine is better (or bigger) than yours. Actually, the choice may be more of how to best adapt what you have.
But single conversion also presents some challenges when trying to fabricate a rig for the higher frequencies especially when trying to use crystal filters that are in the range of 3 to 10MHz. Suddenly, if you are so inclined to use LC Analog VFO's there are some challenges to building a stable 25 MHz VFO.
This is where creativity comes into play as friend N2CQR did with a 10/15M rig. His answer was to homebrew a 25MHz Crystal Filter so with a VFO in the 80M band (3.5 to 4 MHz) you can operate on either band with no sideband inversion. High stability and low frequency drift are the result of the low frequency VFO choice.
But what if you had a really neat 455kHz Mechanical filter and wanted to operate multiple bands. The low frequency filter presents problems in single conversion circuits such as images that start as soon as you move beyond 80M. With the low frequency filters, the use of multiple conversions eases the frequency translation and resolves many of the image issues.
KWM-4 Block Diagram
The above block diagram is for a dual conversion all band SSB/CW transceiver (less 30M) using a Collins 455kHz Mechanical Filter. This is an eye chart and difficult to understand unless you have built dual conversion radios in another life.
Basically, all on the air signals are converted to a 10.7 MHz 1st IF and are passed through a roofing filter (10.7 MHz Crystal Filter +/- 3.75 kHz wide). In a second conversion the signals are mixed with a 10.245 MHz Computer Crystal LO signal to produce one output at 455kHz. From there it is a standard 455KHz IF and so on.
Now on transmit, since this is all bilateral circuitry two mixing products come to the 10.7 MHz Crystal Filter. One is at 0.455MHz + 10.245Mhz = 10.7 MHz and the 2nd at 10.245MHz - 0.455MHz = 9.79MHz which is way outside the crystal filter pass band.
I have had great success with this radio and on the air, reports affirm that it is indeed doing well and if I didn't tell you then you would not know it is a homebrew radio. Check my QRZ page for more photos and circuit descriptions.
Of all the radios I have built only two are multiple conversions including the KWM-4 and a solid-state version of the HW-101 which can be seen here. Thus, most of the time I use single conversion because the frequency translation is made easier with the Arduino/Si5351.
TYGNYBNT
73's
Pete N6QW