An idea for a 10m to 17m Transverter
by IK1ZYW 2001
December 2006. This project has been abandoned. All drawings on paper I had done have been superseded by more modern designs, like the BITX20 and H-mode mixers.
November 2008. I have added at the bottom what I could find on paper of this idea. I have nothing else to add. Sorry.
This is the chronological history of this project, another crazy idea of
mine. At the present I wonder if I will ever come to a finished circuit...
Troubles falling asleep. It comes to my mind that my modified CB for 10m
will soon be unuseful. The sun cycle is supposed to be decreasing,
therefore 10m should be closed all day, soon.
Since this CB serves at my girlfriend's place, when I'm there, I have been
thinking of a way to be on the air even with a low(er) number of
sunspots. I am still considering the purchase of an IC-706 or similar RTX,
but I just had a nice idea.
I remembered some ads on electronic/CB newspapers in 80's: they sold a
transverter from 11m to 45m, all mode (all modes supported by the CB
RTX, of course). I am sure that transverter can be modified
to cover the 40m HAM band. The very next day I was up early searching
the magazine and right after on Internet for such a device. Found it! But
the price is still too high, for gaining just a band (150 EURO or so).
Those days I had read an article by Peter Parker about his direct
conversion receiver that used a combination of analog switches as
mixer (DC-2000 with a 74HC4066 switch). That is not a new idea, but
Peter's article was very well written
There comes my idea: see if any of the XTALs in my junk box can match/mix
my CB RTX coverage (26->28.7 MHz) for any lower HAM band! Hit the
keyboard, prepared a spreadsheet to play with the values.
A low XTAL value would create troubles and many harmonics in the HF
spectrum. So a transverter for 15m is out of question, for now. Higher
would bring me easily onto 30 and 40m, but then I would need a good
amplifier to have my signal heard somewhere. Finally, a 10 MHz XTAL shows
a good combination: 28068-28168 to 18068-18168. WOW! I also like 17
The decision is taken: I'll go for 17m!
Construction started. I decided to begin from the most basic module: the
local oscillator (LO). The block schematic of the whole transverter is
only in my mind, but I am sure the 10 MHz LO is needed. :-)
Construction tecnique chosen is "dead bug", which I also have never tried
Here will be the LO schematic
The LO is a reproduction of Peter's. No big changes, except for a review
(random) of capacitors' values.
Finally assembled the mixer. Actually not all of it, just the 74HC4066, to
see if the idea actually works. My biggest doubt was whether I could actually
traslate upwards the 18 MHz using a 10 MHz sampling. This technique reminds
me of PCM modulation, thus sampling. I would certainly be undersampling
DaDa! It works! Problem: I live in front of FM/TV broadcasts TX locations.
I see them all from my window. We have more than 50 88-108 MHz stations,
and some 30 TV channels (all through UHF band). Damn it! My mixer
brings them down to the HF spectrum! Noise at S7! This makes it extremely difficult to
locate a signal in HF and search for it somewhere else in HF. You need to
find a signal in the space between two FM BC images, and then see if
it's present 10 MHz above. I could locate 2-3 signals in the 16-18 MHz band and listen
to them also on 26-28 MHz. Cool, the mixer works.
Now I need to follow Peter Parker's suggestion and insert ferrite
beads everywhere around the mixer, narrow input filters and hope for good!
Note. I had already noticed that my local oscillator runs at 10004 kHz, so all signals are actually traslated of that amount.
Must be kept into account when using it for the TX transverter and calling CQ!!
Because of a huge lack of time (and instrumentation) this project is currently suspended. If anyone is interested in it, I will honor all requests of schematics, info, suggestions.
Since occasionally I receive some questions about this never born transverter, here is what I have been able to dig out of my pile of drawings:
Click for a larger image
From left to right I planned:
Given the complexity of a Class-A RF chain -at least for me-, right now I would go for the RX converter only, that could be made to work on several bands just changing the L.O. and the input filter, and use a separate XTAL-controlled CW TX.
- 17m bandpass filter (or lowpass)
- RX: RF preamp / TX: class-A RF amplifier chain
- passive double balanced mixer with analog switches, now also called h-mode mixer; driven with a TTL square wave at the 10 MHz L.O.
- RX: a 10m bandpass duplexer, perhaps not needed / TX: an attenuator down to 100-200mW RF (15-20dB)
That's really all, folks!
IK1ZYW, Paolo Cravero. email: ik1zyw at yahoo! dot
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