VHF/UHF performance (and LF/VLF too!)

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Max
Posts: 859
Joined: Thu Aug 13, 2020 9:47 am

VHF/UHF performance (and LF/VLF too!)

#1

Unread post by Max »

Has anyone studied the architecture of the RX888 (or 666 I guess) and concluded what is the likely performance at VHF/UHF? Also LF/VLF?

Question 1:
I guess what I am getting at is what is the likely VHF/UHF performance compared, for example to the low-cost RTL-SDR dongle, or the Airspy R2? Or maybe even the SDR Play RSP receivers?

From Oscar Steila's design it looks like the R820T2 will benefit from the 16 bit ADC? Will this result in a significant performance boost compared to RTL-SDR dongle/Airspy R2/SDR Play receivers?
http://www.steila.com/blog/index.php?co ... id_post=18

Question 2:
What about LF/VLF performance? I'm confused about how low this design goes? Thought I read somewhere it does not receive below 100kHz? Is that right? In the above post, Oscar says 0-30MHz?

Anyone on here with perhaps the RX666 tried VLF yet? Confused about what it will and won't cover. If it goes 0 KHz-1.8 GHz I will simply go ahead and order an RX888 and dispose of my RSP2Pro!

Thanks for looking.

Max

Max
Posts: 859
Joined: Thu Aug 13, 2020 9:47 am

Re: VHF/UHF performance (and LF/VLF too!)

#2

Unread post by Max »

Still interested particularly in the VHF/UHF performance. Is there anyone with the 666 or 888 who has tried it on VHF/UHF and if so first impressions of performance compared to, for example, SDR Play or RTL SDRs, or any other SDRs?

Thanks for looking

Max

PA3BTS
Posts: 28
Joined: Sat Aug 08, 2020 3:02 pm

Re: VHF/UHF performance (and LF/VLF too!)

#3

Unread post by PA3BTS »

Hi Max,

Running a RX-888 here and just exploring it's performance on Band 2 FM with 8 MHz bandwidth, which is the max this SDR can do on VHF. I have compared it with a Elad FDM-S2 at 6 MHz bandwidth. Both SDR's on the same antenna using a RF Systems SP-3 splitter. First of all I figured out the best SNR for the RX-888 by adjusting the VHF gain. Visual gain was set to -20dB. VHF gain setting 16 turned out to be the best.
This gave a noisefloor of about -115dBm. Next I adjusted the visual gain of the FDM-S2 to show a noisefloor of -115 dBm as well to make visual comparison easier.
I used the analogue meter showing SNR values to compare.
It turned out that the FDM-S2 outperforms the RX-888 by 1 dBm or less on 88.0 MHz Radio 2, a strong local.
On 107.1 MHz Deutschlandfunk Bremen the difference was about 4 dBm in favour of the FDM-S2. Readability of the weak signal was significant better on the S2, with less noise.
Next was a RDS count on 87.7 Radio 10, medium strength signal but influenced by 87.6 MHz Radio 10 which always gives RDS reading trouble. The count in the RDS logfile was the same, but the FDM-S2 was slightly better in decoding station info.

Hope this is of any use.

73, Cornel

Max
Posts: 859
Joined: Thu Aug 13, 2020 9:47 am

Re: VHF/UHF performance (and LF/VLF too!)

#4

Unread post by Max »

Many thanks Cornel. Much appreciate the information and all very useful. For my sort of usage from your description I think it sounds like the RX888 will be adequate.

Still also interested to hear from anyone who has used for amateur bands 50/144/432 or whatever?

73

Max

PA3BTS
Posts: 28
Joined: Sat Aug 08, 2020 3:02 pm

Re: VHF/UHF performance (and LF/VLF too!)

#5

Unread post by PA3BTS »

Hi Max,
I checked the RX-888 against the Airspy R2, with the Airspy set in Sensitive mode.
On 145.575 Mhz the Airspy and the RX-888 are on par.
On a local 424 MHz data signal the Airspy is about 6 dBm better in SNR.
On a local repeater at 430.125 MHz the Airspy R2 is 8,5 dBm better.

73, Cornel

Max
Posts: 859
Joined: Thu Aug 13, 2020 9:47 am

Re: VHF/UHF performance (and LF/VLF too!)

#6

Unread post by Max »

Hi Cornel

A little as expected, so not the best result but usable for casual stuff on UHF I guess. I am not a huge UHF user and more likely to want reasonable performance on 50, 70 and 144 MHz so it is still of interest for sure as I am also mostly on HF anyway.

Many thanks again for coming back with the information and is all useful.

73

Max

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NO6B
Posts: 53
Joined: Wed Aug 19, 2020 7:06 am

Re: VHF/UHF performance (and LF/VLF too!)

#7

Unread post by NO6B »

Wonder what would make the 888 fall apart at UHF. Doesn't it use the same front-end on VHF/UHF as the R2?

Still waiting for my 888: ordered it a few weeks ago, just shipped a few days ago.

G6PZZ
Posts: 26
Joined: Sun Aug 16, 2020 6:05 am

Re: VHF/UHF performance (and LF/VLF too!)

#8

Unread post by G6PZZ »

I am still wondering how suitable it might be for Broadcast VHF and DAB DX.
Has anyone tried this?

User avatar
NO6B
Posts: 53
Joined: Wed Aug 19, 2020 7:06 am

Re: VHF/UHF performance (and LF/VLF too!)

#9

Unread post by NO6B »

OK finally got mine & have been testing it on VHF/UHF. For some reason it's not very sensitive on VHF/UHF. The best NBFM 12 dB SINAD I can get out of it is 0.6 uV & that's with the RX-888 ExtIO & HDSDR. That ExtIO has 3 separate gain controls so you can fine tune the front-end similarly to the RTL SDRs. Right now there's only one VHF gain slider in SDRC (will be posting a request for more controls in the appropriate group shortly), & with SDRC the best achievable S/N is a couple dB worse. Adding a preamp helps a lot but again you need more control of the front-end to get the most out of it, otherwise you have to lower the gain to the point that you lose 3 to 5 dB of sensitivity over what you can get with just a signal generator connected to it.

There's little doubt in my mind that the R820T2 is holding the RX-888 back in the VHF/UHF range, so unless you plan on making your own downconverter to HF so you can make the most use of the 16 bits I'd say no.

fei666888
Posts: 18
Joined: Sun Oct 04, 2020 8:54 am

Re: VHF/UHF performance (and LF/VLF too!)

#10

Unread post by fei666888 »

In my test, I found that the heat of R820T2 will cause the reception performance to decline. On the other hand, we did not turn on the internal Mixer gain adjustment of R820T2, only the gain control of LNA and VGA was turned on. We will add it to the new version of RX888 extio This option

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