Should I always have both antennas on Deity Theos rx?

[u/d0inmabest]

I've been using my Deity Theos kit (Global, I'm in Canada) for quite a while now, maybe a couple of years. I had to replace one of the transmitters because the mic input got messed up (tried getting it fixed twice by a local electronics store but problems persisted). They ended up giving me 35% off because it took forever to get support for them. Anyway, I've been noticing lately that I'm getting more dropouts, even when the rx is close by. (I feel like I had better performance when the original tx was operational, I used to remark how well it held the signal even behind closed doors).

I've mostly been only needing one tx lately so I've just been using one antenna on the rx. On my last project the last two days I had to mic two people so was using both antennas on the rx...I left both on even when only one tx was being used and there didn't seem to be any dropouts at all. So this had me wondering, is it possible that by having both antennas on even when only one tx was being used improved the performance? I wouldn't think that would make sense because they're different frequencies, so what does it matter? I'll do some testing on this but wanted to see what others thought.

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[u/Run-And_Gun]

I've mostly been only needing one tx lately so I've just been using one antenna on the rx.

That's not how that works.

[u/d0inmabest → u/Run-And_Gun]

I'm learning that! Thank you. Will always have both antennas on from now on!

[u/kirabella2000]

Deity D2RX’s use some sort of diversity reception. Precisely what type of diversity reception I haven’t been able to confirm. You definitely want both antennas connected.

[u/Vuelhering]

I don't know how the Theos works, but every other receiver I've used always requires both antennas.

When a signal takes two paths it can cause destructive interference. In other words, if a signal goes to one antenna directly, but also bounces off a metal wall and takes a very slightly longer distance, both signals will hit the antenna and if the sine wave on one is a peak while the other (slightly delayed signal) is a valley, the entire signal disappears when they both hit the antenna. By using two antennas, slightly apart (usually at least half a wavelength difference iirc), the distance is changed enough that using the strongest signal and switching between them will avoid most dropouts.

Most manufacturers use clever means to deal with this. There's also issues with polarity/phase and such, and you'll see several mixer setups that use multiple antennas positioned 90 degrees from each other. I have been known to put one LPDA at an angle, if it has a good enough view of the set. Signals tend to have an orientation based on the transmitter's antenna, and being at the wrong orientation causes a much weaker signal.

Basically, if you ever see the word "diversity" on the spec sheet, it requires both antennas for however many channels.

Edit: Here is a discussion from Lectro on it, although it doesn't give a great ELI5 description.

[u/d0inmabest → u/Vuelhering]

Thanks a lot! It's funny, I actually have an Electronics Technology diploma specializing in telecommunications...I mean, I graduated from that in 1999 and never made use of that education. That's my excuse anyway. OK, both antennas on!

[u/PhforAndAfter]

Read the manual

[u/Econormics]

I'm almost certain that D2RX uses an antenna diversity algorithm.

Which means that each of the two receiver circuits will assign reception to the antenna with the strongest signal.

I am unsure if it can do that independently of each respective transmitter. Meaning it is using the strongest antenna of the two antenna inputs regardless of you using one, or two transmitters.

While Deity sometimes refers to this as "true diversity" it is unlike some true diversity systems that have two receiver modules per channel (e.g. a two channel receiver has 4 receiver circuits, two per channel).

With this type of diversity, the algorithm selects which receiver module AND which antenna provides the "best" signal per channel.

With all that said, when operating an antenna diversity system with one transmitter, where both antennas are oriented exactly the same way, and so close to one another on the RX, I'm not sure using that both antennas makes much difference "technically", except that the algorithm may be optimized for using both antennas.

That would not be the case if you were connecting external omni or directional antennas with a quarter-wave or more distance between them. In this use case, there is little question that using both antenna inputs is be a better option.

In my experience, every wireless system has its unique quirks, and it is up to you to do exactly what you're doing by trying different configurations to optimize the system.

That said, the manufacturers have a detailed understanding of what's going on under the hood. So the product manual is a solid starting place and then go from there. Just don't experiment on an actual production 😉

[u/d0inmabest → u/Econormics]

Thanks...using both antennas at all times seems the way to go.

[u/bergante]

The user manual, page 8, includes a drawing for the D2RX receiver. Curiously both SMA antenna connectors are labeled as "Anenna Socket, Diverisity(sic) Section A". And on page 18 there are some recommendations for antenna orientation but no mention of diversity at all.

Being a digital system, assuming it is based on a SDR design, I imagine you can implement proper diversity using just two receiver circuits for two channels.

But there is no mention of diversity.

[u/timothys_monster]

I am pretty sure that the D2RX is precisely NOT using any form of diversity. Can any one of you proof that they would? I have been trying to get official info on it but never found the mention of a diversity system in this line of receivers.