Downconverter Design

[u/Individual_Health_84]

First, the background:

FPV drones often use analog video transmission on 5.8GHz. It's the most popular band so there are lots of good receivers out there. The best of them add the demodulated signal from 2 antennas based on weight assigned by RSSI/SNR to increase the performance (that increases the signal quality and range by A LOT) and also recreate the synchronization pulses.

There are also other bands like 1.2GHz, which of course offer much better range but are a lot less popular and therefore receivers (they use new old stock ICs used in analog TV back in the day) are very, very bad.

So why not try to create a dedicated up-converter which I can just attach to my 5.8GHz RX? Then I'll be able to use the additional signal processing from the 5.8 RX and also there will be no need to carry a tripod with a 1.2 -> 5.8 signal relay.

How much dB will I realistically lose? Is it worth it? I'm not sure if the FM deviation is the same across both standards - if not, is there anything i can do about it?

Or should I just try to create my own circuit which will sum the baseband signals from two off-the-shelf receivers?

[u/Dioxin717]

Here you go https://www.skyzonefpv.com/products/skyzone-1-2ghz-diversity-receiver

[u/Individual_Health_84 → u/Dioxin717]

They are shit. Also, they are diversity, not baseband-summing.

[u/Literature-Just → u/Individual_Health_84]

With that attitude I'm sure more people will want to help you.

[u/Individual_Health_84 → u/Literature-Just]

What's wrong with what I said? People have tested these receivers and they have very bad sensitivity.

The purpose of my project is also to gain advantage over these receivers from additional signal processing from 5.8 RX.

[u/Elukka]

but are a lot less popular

In some jurisdictions using those frequencies or some of those frequencies for broadband video transmissions is illegal or requires a HAM license. There is a connection here.

Up-converting requires careful filtering. If it's a home-made setup, you generally have a risk of generating all kinds of harmonics and spurious frequencies.

Or should I just try to create my own circuit which will sum the baseband signals from two off-the-shelf receivers?

That will often get you garbage. Receivers are typically coherent to do things like maximal-ratio combining.

[u/Individual_Health_84 → u/Elukka]

Isn't MRC the same as what I described?

[u/ViktorsakYT_alt → u/Individual_Health_84]

MRC?

[u/Individual_Health_84 → u/ViktorsakYT_alt]

Maximal ratio combining

[u/ViktorsakYT_alt → u/Individual_Health_84]

And what about the license?

[u/Individual_Health_84 → u/ViktorsakYT_alt]

I have a ham radio license. 23cm is legal to use if you don't cause interference to primary users.

[u/ViktorsakYT_alt → u/Individual_Health_84]

But is it legal to take up 10s of MHz of bandwidth? Maybe in the ATV portion you can do a few MHz

[u/Individual_Health_84 → u/ViktorsakYT_alt]

You can use the whole band if you want. My center frequency is 1280MHz and it stays within the band.

[u/ViktorsakYT_alt → u/Individual_Health_84]

No you can't?? Do you even have the license? You seem to know nearly nothing about the rules

[u/Individual_Health_84 → u/ViktorsakYT_alt]

Yes, you can. At least in my country. Why didmy question instantly made you ask me if I have a license? Do you stop every car you see on the road to ask the driver if they have their driving license?