Архив за 12.08.2017

Dish antenna polarization question

I plan on attempting to recieve and decode Inmarsat AERO messages using my RTL-SDR blog dongle, outernet lna, and outernet patch antenna, but I also have an offset directv dish that I can mount on a tripod. I want to use the patch antenna as a feed while the dish reflects the signal. I am aware that Inmarsat's polarization is RHCP. But I was also concerned since the rtl-sdr.com article said it reflects the polarization so it is LHCP when reflected by the dish. Is this true? And if so, how much signal loss is there when recieved with an RHCP antenna.

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Comment on Our Review of the Airspy HF+: Compared against ColibriNANO, Airspy Mini, RSP2 by Larry Dighera

Here are comments from Adam Farson and Rob Sherwood:
—–Original Message—–
From: Adam Farson [mailto:farson@shaw.ca]
Sent: 19 July, 2017 13:45
To: ‘Rob Sherwood.’
Subject: RE: Airspy HF+

Rob, Larry,

Just looked over the Airspy HF+ web page. Firstly, a look at the block
diagram tells me that this is a superhet receiver, with analogue mixers and
LO’s for HF and the two upper bands feeding IF’s into an ADC. Hence the
“image rejection” term is relevant. (As an aside, the non-native English
writing style of the website is a little weird.)

No RMDR value is stated, but the specified 100 MHz phase noise value does
not look too good when expressed as RMDR.

“Very low phase noise PLL (-110 dBc/Hz @ 1kHz separation @ 100 MHz)”.
Assuming B = 500 Hz, this resolves to 83 dB RMDR – less than stellar by any
account.

The device appears to have a varactor-tuned tracking preselector. Due to
parametric effects in the varactors under strong-signal conditions, this can
be a horrendous IMD generator, as we saw with the early JRC receivers and
transceivers.

Rob, I agree completely with your comments regarding receivers vs.
transceivers and the uses to which dongles are put. For HF and 6m, I believe
that the Russian Colibri Nano is a much more interesting device than the
Airspy. It is a 14-bit direct-sampler. Here is my Nano test report:

http://www.ab4oj.com/sdr/sunsdr/nano_notes.pdf

I am more than willing to test serious contenders in the receiver world. For
example, Icom Canada will loan me an R-8600 for testing, probably next
month. I am no longer motivated to test any purely legacy architecture;
although I am retired and have more available time, I do have a life outside
my little 6.5m2 lab.

73, Adam VA7OJ/AB4OJ

—–Original Message—–
From: Rob Sherwood. [mailto:rob@nc0b.com]
Sent: 19 July, 2017 12:28
To: Larry@kj6yvt.com; farson@shaw.ca
Cc: sdrsharp@yahoo.com
Subject: RE: Airspy HF+

Hi Larry,

Just a couple of comments. IP3 is a meaningless number for a direct
sampling radio. I also don’t understand the meaning of “image rejection” as
applied to a DS SDR.

There must be quite a bit of preamp and/or ADC driver gain to push the noise
floor down to the levels quoted. What is the ADC overload value in dBm for
any preamp settings?

What is the phase noise at 10, 20 and 100 kHz on 20 meters? That is likely
more important than at 1 kHz offset where in reality if listening to a weak
CW signal next to a very strong CW signal, the adjacent signal’s key clicks
will dominate before phase noise.

Is there an RMDR spec for the receiver at 2 and 20 kHz, as is now usually
quoted in any review in QST?
One would expect the RMDR value to be HF ham band independent.

When I was writing for Passport to Worldband Radio for its 25 years of its
existence as their laboratory, receivers as opposed to transceivers would
have been of prime importance. Today with a significant drop in shortwave
broadcasting, I don’t think the shortwave market is a shadow of its former
self.

On the other hand, SDR dongles are being used for spectrum scope for
transceivers missing this feature, and for CW Skimmer and reverse beacon
reception.

At present with new product announced at the Dayton Hamvention, I am only
planning to test DS SDR transceivers this year. Examples: Icom IC-7610,
Flex 6600M, Apache ANAN 8000DLE, and a second and possibly a third sample of
the Elecraft KX2. I have the second KX2 here now in my possession as of
last evening.

Adam may have more time than I for testing receiver only products, as I am
still working part time with a sub set of my IT client base, at least for a
few more years.

73,
Rob Sherwood
NC0B

—–Original Message—–
From: Larry Dighera [mailto:Larry@kj6yvt.com]
Sent: Wednesday, July 19, 2017 9:55 AM
To: Rob Sherwood. ; farson@shaw.ca
Cc: sdrsharp@yahoo.com
Subject: Airspy HF+

Gentlemen,

I’d be interested in your opinions on this new entry into the SDR market, as
I’m sure many others would be also. You may be able to request a sample for
testing from: sdrsharp@yahoo.com

Technical specifications

HF coverage between DC .. 31 MHz
VHF coverage between 60 .. 260 MHz
-138 dBm MDS at 500Hz bandwidth in HF
-142 dBm MDS at 500Hz bandwidth in VHF
+26 dBm IIP3 on HF at maximum gain
+13 dBm IIP3 on VHF at maximum gain
110 dB dynamic range in HF
95 dB dynamic range in VHF
120 dB Image Rejection
0.1 dB Spectrum Flatness
0.5 ppm high precision, low phase noise clock
660 kHz alias and image free output
18 bit Digital Down Converter (DDC)
+10 dBm Maximum RF input
Very low phase noise PLL (-110 dBc/Hz @ 1kHz separation @ 100 MHz)
2 x High Dynamic Range Sigma Delta ADCs @ up to 36 MSPS No Silicon RF switch
to introduce IMD in the HF path Routable RF inputs Wide Band RF filter bank
Tracking RF filters Sharp IF filters Smart AGC with real time optimization
of the gain distribution All RF inputs are matched to 50 ohms
4 x Programmable GPIO’s
No drivers required! 100% Plug-and-play on Windows Vista, Seven, 8, 8.1 and
10
Industrial Operating Temperature: -45°C to 85°C

Best regards,
Larry
WB6BBB

Handheld directional antenna for finding the source of a signal on my RTL-SDR?

I used my RTL-SDR to find an interesting signal just below the FM band. I'd like to know where it is coming from. Can you recommend a handheld antenna (Amazon is fine) in the 50-100MHz range that I can point around me to location the direction of a signal?

My attempts to find a suitable directional antenna resulted in ones that were way too large, or were outside the frequency range. I appreciate the help. If it turns out to be interesting, I'll share my findings. :)

submitted by /u/Atari_Historian
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Comment on Our Review of the Airspy HF+: Compared against ColibriNANO, Airspy Mini, RSP2 by Paul

You see a lot of problems for $149 ! I see a lot of great DX opportunites 🙂

(hope your shift key still works btw)

Comment on Our Review of the Airspy HF+: Compared against ColibriNANO, Airspy Mini, RSP2 by bloody paywalls

It is a real pity that most of the documents I can find are behind pay walls, but the abstract for at least one of them (“Distortion cancellation by polyphase multipath circuits”) does sound interesting:
“It is well known that in balanced (or differential) circuits, all even harmonics are canceled. This cancellation is achieved by using two paths and exploiting phase differences of 180/spl deg/ between the paths. The question addressed in this paper is: what distortion products (harmonics and intermodulation products) are canceled if more than two paths (and phases) are used? These circuits are called polyphase multipath circuits. It turns out that the more paths (and phases) are used, the more distortion products are canceled. Unfortunately, some intermodulation products cannot be canceled without also canceling the desired signal. An analysis of the impact of mismatch between the paths shows that the suppression of distortion products will be larger if more paths are used. As an application example, the design of an upconversion mixer with a clean output spectrum is presented.”

Comment on Our Review of the Airspy HF+: Compared against ColibriNANO, Airspy Mini, RSP2 by Drone

Where are the DETAILS??

Schematic and BOM, NO (A BIG PROBLEM)
L.O. phase-noise, NO (only at 1KHz offset)
External L.O. ref. input, NO (A BIG PROBLEM)
Rx noise figure vs. freq., NO
Rx ret. loss vs. freq., NO
AGC range details vs freq., NO (A BIG PROBLEM)

The worst thing about this “new” design is a lack of DETAILS about this HF “polyphase harmonic rejection (HR) mixer”. MORE DETAILS PLEASE!

This SDR seems to target the HF band. But yet there is NO external reference connector. HF work today is VERY centered on small-signal work, especially when it comes to very narrow band digital modes. By not providing an external reference clock input, this design is an EPIC FAIL when it comes to small signal work.

Without more DISCLOSURE about this “new” product, I would NOT recommend purchase. Web “reviews” are one thing. KNOWING how a product actually works and why is FAR more important.

Comment on Our Review of the Airspy HF+: Compared against ColibriNANO, Airspy Mini, RSP2 by Paul

I think in this case the mentioned AGC is pre-ADC, adjusting the HW gain stages in a smart/selective way. Don’t think DSP AGC will be in the same loop, so you can still adjust and disable your AGC like you are used to.

С недавнего времени периодически стала наблюдаться нестабильная работа донгла и\или Шарпа — после 8-10 ч работы перестае…

TopGun пишет:
С недавнего времени периодически стала наблюдаться нестабильная работа донгла и\или Шарпа - после 8-10 ч работы перестает поступать сигнал в программу (или программа перестает его принимать), хот...
читать полностью...
Широкополосный приёмник из DVB донгла - Страница #517

-- Delivered by Feed43 service

Recently certified radio amateur looking to get started with SDR

Hello! I got my amateur radio license over a year ago. I live in an apartment building with no access to the roof and there have been so many obstacles keeping me from getting started with that. HF is nearly impossible due to lack of roof access, so I bought a handheld UHF-radio, but I just keep scanning without ever finding anything going on.

Now I heard that SDR can be used for more efficient scanning(?) and that you can have fun with that even if you don't necessarily have huge antennas on your roof. What are good resources to get started, what should I purchase etc? Any advice would be greatly appreciated!

submitted by /u/gypsyharlot
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Comment on Our Review of the Airspy HF+: Compared against ColibriNANO, Airspy Mini, RSP2 by rwgast

I would really like to see what is under the RF Shield, is there any possibility you can desolder and take some pictures for us?

I currently have a few LTC2217 105msps/16bit ADC’s I planed on building a DDC receiver with and I would like to see what the HF+ is doing for DDC without using an FPGA. Im also interested to see if its mixer is handmade or an off the shelf product. My interests are decimating large ADC samples all the way down to very narrow band channels to get the best SNR possible.

Im in to Radio Astronomy, and weak interstellar signals. I’ve been looking in to getting a DDC receiver like the Net-RF line or even a HPSDR stuff, so I would have a very good platform to mix 407mhz/1420mhz/8ghz down too. The problem is they are so much more expensive than my airspy, and the performance edge a DDC receiver gives isn’t worth an extra $900 dollars, at least to me! Im really impressed with this HF+ and I thought it may be the ticket (especially since im use to the airspy api) but if you cant disable AGC I have to pass, unless a firmware mod adds manual gain down the line. If I cared about receiving HF for HF radio sake though by far this is one of the best HF SDRs besides maybe FLEX I have seen. Im surprised it did so much better than the Calibri, which I have also considered as an off the shelf solution for myself. These guys just keep pumping out great hardware for the price if they stay on this path they will be a huge player when SDR is the main stream. I just wish there core software was a little more open or Linux friendly.

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