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Topic: VHF/UHF to HF down-converter (Read 29844 times) previous topic - next topic

Re: VHF/UHF to HF down-converter

Reply #15 –
Hmm. If i use a single-chip solution instead of building an image-rejection mixer scheme (Hartley or Weaver) from building blocks, there should be plenty of space on the board to use multiple chips for different frequency spans and have them switched in and out of the signal path... Good idea :)

Now if i just need to find ones with good enough specs and find equally good hybrids for each span, that i can use to sum the I and Q signals...

Although even then, some prefiltering will probably be needed (and some careful band-planning). The best that these demodulators seem to be able to pull off is about 0.5 deg phase error and a few hundred mdB of amplitude error, meaning the best IRR i can hope to get is some... what... 50ish dB?

Also, the Si570 will probably have to go and be replaced by a PLL VCO, as Si570's output is a square wave. Switching mixers such as the ones i've been planning to use are fine with that. The ones in demodulators... i'm not so sure.

Re: VHF/UHF to HF down-converter

Reply #16 –
[quote author="orcinus"]Also, the Si570 will probably have to go and be replaced by a PLL VCO, as Si570's output is a square wave. Switching mixers such as the ones i've been planning to use are fine with that. The ones in demodulators... i'm not so sure.[/quote]

the si571 has differential output, it can easily be filtered through a transformer for a sign wave.

Re: VHF/UHF to HF down-converter

Reply #17 –
Si570 does too. It depends on the logic level version.
CMOS doesn't have differential, LVDS, ECL and CML do.

I've included a transformer in the original block diagram for that purpose, but still, there would quite probably be leftover harmonics leaking through.

Re: VHF/UHF to HF down-converter

Reply #18 –
Slightly OT, but came across this while looking for down-converter components:
http://www.analog.com/en/rfif-component ... oduct.html

It's a single chip wideband (75-1000 MHz) transmitter. Thought it might be useful for your transciever project, sqkybeaver :)

Re: VHF/UHF to HF down-converter

Reply #19 –
These two seem interesting:

http://search.digikey.com/us/en/product ... -ND/890398
http://search.digikey.com/us/en/product ... ND/2052214

First one covers RF from 40-500 MHz, the second one from 400-3900 GHz.
The second one would require some more components to be switched in and out of the signal path (balun between it and the antenna, for one). I haven't gotten around to reading the spec sheets properly yet.

Also not sure about their quality. The THD of the first IC seems kinda high...

Re: VHF/UHF to HF down-converter

Reply #20 –
Scratch that, the Skyworks IC has a pretty high phase error (+-3 deg).

Re: VHF/UHF to HF down-converter

Reply #21 –
the lt5506 would be an ideal for the 6,2meter and 70cm bands, as a single receiver option.

is there a transmitter similarly specked?

i'd like to put together a test platform for something like this, and try my hand at RF layout.

it could fit the 4meter and 220 bands in as well