6 meter band receivable ?

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N8CVW
Posts: 28
Joined: Sat Jan 02, 2021 7:28 pm

6 meter band receivable ?

#1

Unread post by N8CVW »

Hi All,

Does 3.1 support reception of 6 meters ?

If so, how to do ?

TIA !

Paul
N8CVW

N8CVW
Posts: 28
Joined: Sat Jan 02, 2021 7:28 pm

Re: 6 meter band receivable ?

#2

Unread post by N8CVW »

with regard to RX888 Mk2,

in case that wasn’t clear from posted in RX888 forum

N8CVW
Posts: 28
Joined: Sat Jan 02, 2021 7:28 pm

Re: 6 meter band receivable ?

#3

Unread post by N8CVW »

ok, 6 meter coverage awaits direct sampling being extended to 64 MHz, already in the request/development queue I believe

has Simon mentioned an ETA ?

can anyone tell me the current sampling rate ?

Max
Posts: 858
Joined: Thu Aug 13, 2020 9:47 am

Re: 6 meter band receivable ?

#4

Unread post by Max »

Paul

See here:

https://www.sdr-radio.com/rx-666

As far as I can see it's 32MHz. See also the other links in the above url page, specifically this one:

https://dk8ok.org/2020/09/04/rx-888-32- ... your-ears/

73

Max

N8CVW
Posts: 28
Joined: Sat Jan 02, 2021 7:28 pm

Re: 6 meter band receivable ?

#5

Unread post by N8CVW »

Hi Max

I observe that bandwidth selection extends up to 32 MHz . Being direct sampling at baseband this limits coverage to 32 MHz.

I understand that along with several other changes introduced with the Mk2 hardware version that direct sampling was enabled for up to 64 MHz, that being about the Nyquist limit for the 130 MSPS LTC2208 ADC along with a 64 MHz low pass filter.

I've seen some mention that some have succeeded with 64 MHz bandwidth under HDSDR (?- if I recall correctly),

and also some talk that Simon plans to extend the direct sampling coverage to 64 MHz.

My question is, does anyone know when this might appear ?

Will this will require streaming quite a wide bandwidth 54~55 MHz for achieving 6 meters coverage, which will be very challenging for the PC platform : 130 MSPS x 4 bytes/sample = 520 MB/s (?)

However, currently it is supported to choose a bandwidth ( 1, 2, 4, 8, 16, 32 MHz ) and display any portion of the spectrum up to 32 MHz,

so this suggests that it will NOT be necessary to stream the entire 64 MHz bandwidth (?)

I expect there are other implementation challenges, such as increased thermal loading at 130 MSPS rate.

Any info, update, or advice from anyone is greatly appreciated,

Kind thanks for your response !

Paul
N8CVW

Max
Posts: 858
Joined: Thu Aug 13, 2020 9:47 am

Re: 6 meter band receivable ?

#6

Unread post by Max »

Surely yes this is correct. Direct sampling will be available up to 64 MHz but in the "slice" width of your choosing of your choosing, 1,2, 4 etc., but with the difference being that the upper slice width will be 64MHz, not 32MHz, as surely is the case now up to 32MHz?

e.g. Hermes Lite 2 is direct sampling to 38.4 MHz, but only in slices of maximum width 384 KHz. So no, cannot think of any need to sample full 64MB/s just to be able to receive at 50MHz. That would be a waste of PC resources!

So yes, you will need to wait for Simon's updated kit if you wish to direct sample at 6m, but you can receive now at up to 10MHz bandwidth (down converted - not direct sampled) by using the built-in tuner/down converter/front end.

But no, can't think of any reason why it would be needed to direct sample at full 64 MB/s bandwidth just to receive a 2MHz (direct sampled) slice at 50 MHz

Or maybe I misunderstand your question?

73

Max

N8CVW
Posts: 28
Joined: Sat Jan 02, 2021 7:28 pm

Re: 6 meter band receivable ?

#7

Unread post by N8CVW »

Would it be correct to say there’s a DDC function that “slices” the incoming stream ?

As I understand the RX888Mk2 specs, the V(hf) antenna port starts at 64 MHz,

and given that direct sampling currently ends at 32 MHz,

the 32-64 MHz spectrum is not accessible presently

(?)

Max
Posts: 858
Joined: Thu Aug 13, 2020 9:47 am

Re: 6 meter band receivable ?

#8

Unread post by Max »

No, not what I would understand to be the case. Direct sampling up to 64 MHz. Above that it uses the built in tuner/down converter.

So you will be able to tune 50 MHz but not in any bandwidth greater than a 32 MHz "slice", i.e. you will be able to hear 32MHz to 64 MHz in one slice (or 30-62 or 28-60), should you so wish and have the computing power to accept a stream of that bandwidth. My guess is you will need a chunky computer to even manage 32 MHz bandwidth.

What Simon has not yet done is to allow you to monitor in one sampled band of 0 to 64 MHz. I think there's some confusion here between the available span of the receiver and how much of it you can receive in one uninterrupted live "slice"/datastream.

RX888 Mk2 owners please chip in if I have this wrong? Joanne?

73

Max

N8CVW
Posts: 28
Joined: Sat Jan 02, 2021 7:28 pm

Re: 6 meter band receivable ?

#9

Unread post by N8CVW »

I’ve jumped to wrong conclusions !

trying it out, there IS 6 meter coverage !

I think what happened was that the Aliexpress product description stated 1KHz - 64 MHz , but also stated “maximum 64 MHz real time bandwidth”

so I supposed that as there is only a 32 MHz bandwidth and therefore 32-64 is not available

but it is !

sorry for my confusion and thanks for your input!

Paul
N8CVW

Max
Posts: 858
Joined: Thu Aug 13, 2020 9:47 am

Re: 6 meter band receivable ?

#10

Unread post by Max »

NP Paul. Yes, I guess it is a somewhat confusing description. As you have seen it's the difference between the frequencies at which direct sampling is available and how much of that area you can sample in one go that I think was causing your confusion. My guess is that even if available sampling 64 MHz in one slice will take huge resources from the PC. Some people want it but don't think necessary for most users. I exist quite happily with my 384 kHz "window", but direct sampled on my Hermes Lite 2 transceiver.

Out of interest, how do you rate the RX888? I've come very close to buying one on several occasions but slightly put off by the somewhat clouded view of who is actually manufacturing them. Never really got a clear answer as to whether it's lots of small Chinese manufacturers effectively "home building" them in which case my guess is the quality will be quite variable, or if they come mainly from one original source (Justin Peng himself maybe?).

I've also decided to postpone because Simon has spoken of some other direct sampling masterpiece due to appear from another mainstream manufacturer, but release date seems to keep getting put back and we don't get to know who it is that's due to make it!

73

Max

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