Implementing diversity RX on transverters?

Discussion in 'Software Defined Radio (SDR)' started by K3RW, May 1, 2021.

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  1. K3RW

    K3RW Premium Subscriber QRZ Page

    I'm curious if anyone is running diversity reception in conjuction with a transverter. Not just for EME. Mainly I *think* that means running two transverters... one for each side of the diversity RX. Am I right

    I had planned to run a Moxon and a vertical on diversity for HF. But I don't need a transverter for that. So it gets tricky.

    Its a little less clear to me when dealing with a SDR that goes from, say 28 MHz to any transverter. Especially 28MHz to a low drive 144 MHz IF to, say a 10GHZ transverter. Or even 23cm instead of 10GHz. Running something simpler like a 2m pair on a 28MHz IF knocks out the half transverter-to-transverter issue. Running a 10GHz transverter to a 28MHz does as well. It just limits selection considerably.

    Plan on my end eventually is to run 10GHz EME with diversity RX. An Elmer wants to run other bands on diversity RX. Running arrays on EME is far from innovative, but combining it with diversity RX on a SDR has little guidance. The big guns usually switch polarity but running SDRs are fairly new and diversity running digital modes is very new.

    Digital EME may help overcome some issues we're stuck with but also induce others. But that means everything has to be tied together well. Seems hard to do with 2 transverters, so hence the question.
     
  2. SM0AOM

    SM0AOM Ham Member QRZ Page

    Generally speaking, there are four major forms of diversity that may be employed;
    • Frequency diversity
    • Time diversity
    • Space diversity
    • Polarisation diversity
    All are built on the principle that the fading patterns of the separate paths are uncorrelated so when there is a null in one path the signal remains in the other.

    The only forms that may be implemented using only one transverter are frequency diversity and time diversity, the remaining need independent signal inputs and processing chains for each path.

    An issue when designing diversity schemes using separate inputs is to preserve phase coherence between the physical channels so the diversity combining algorithm also may use phase information.

    It takes special considerations when designing the clock generation and distribution networks.

    73/
    Karl-Arne
    SM0AOM
     
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  3. W1VT

    W1VT Ham Member QRZ Page

    Many of the "no tune" designs featured mirror imaged circuit board layouts for receive and transmit. Jim Davey WA8NLC designed hairpin 3456 MHz filters on Teflon circuit board for use with the newly available MMICs.
    Rick Campbell KK7B expanded the concept to other bands. These boards should make it easier to design a diversity receiver as the mirror imaging should preserve the phase coherence with a minimal amount of effort.
    Down East Microwave sold transverters and converters designed by Jim and Rick.

    Zak W1VT
     
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  4. K3RW

    K3RW Premium Subscriber QRZ Page

    What would be different about the clock and distro network? Would it need something like a delay or phasing line?
     
  5. K0UO

    K0UO Platinum Subscriber Platinum Subscriber QRZ Page

    I use Diversity Receive 100% of the time. And I talk to several other stations doing the exact same thing daily. We prove it daily with poor band conditions, diversity works. It's not always signal strength but signal usability, several of us use Beverage antennas on the lower frequencies.

    With two Icom 7610s (Icom did it right) using the new Diversity Tracking Function, and attaching separate antennas to the antenna ports in the Tracking receive mode, you have true "Diversity Receive". It is a fantastic Improvement in reduction of QSB/fading. On HF as the ionospheric geometry changes with time, the arrival time, angle and polarization of incoming signals will also change. If one antenna is experiencing a deep fade, it is likely that another has a sufficient signal. Pattern diversity consists of two or more co-located antennas with different radiation patterns. This type of diversity makes use of directional antennas that are physically separated by some distance.

    Diversity for skywave is just as effective with two antennas with the same-polarization but they must be spaced a number of wavelengths apart. Spatial diversity employs multiple antennas, usually with the same characteristics, that are physically separated from one another. Phase Synchronous Diversity Reception uses two widely spaced antennas (500 to 1500+ feet) feeding two identical high performance SDR receivers. A radio signal can be reflected along multiple paths before finally being received. Each of these bounces can introduce phase shifts, time delays and signal strength attenuation that can destructively interfere with one another at the receiving antenna. Depending upon the expected incidence of the incoming signal, on the order of a many wavelengths. Collectively they are capable of discriminating a large portion of angle space and can provide a higher gain versus a single omnidirectional radiator.

    The difference can be as much as a signal being useable in Diversity, to poor or no readability without.

    When signal-to-noise ratio is marginal, diversity can be make all the difference in the world on readability.

    Diversity reception techniques is used to mitigate the effects of ionospheric multi-path fading, shadowing and signal drop-outs (path loss) which serves to enhance the overall signal-to-noise ratio and readability of received signals. This is absolutely a major improvement, with Diversity Receive I use over a mile of wire listening to signals coming in at different angles. Signal-to-noise ratio (S+N/N ratio, or SNR) is one technical aspect not too many amateurs give a second thought about, however if you can't hear them you can't work them. This is very apparent on audio reception, Diversity eliminates much of the audio amplitude fading. The RF signal is almost never in a stable phase relationship at both places at the same time. This means the signal will have random phase and amplitude differences. The arrival angle and polarization of incoming signals will change and this generally results in the fading, by having two antennas, the chances are that while one experiences a fade, the other will not. The power is in the diversity.
    My antennas are spread out over half a mile. but I have several friends using antennas much closer together with good results.


    Icom did it right on the IC 7610, Stereo/Dual Diversity + Antenna/Space Diversity + Polarization Diversity Reception.

    Good DX to you.
    73 from, The K0UO " Rhombic Antenna Farm"
     
    Last edited: May 1, 2021
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  6. K6CLS

    K6CLS Ham Member QRZ Page

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