Digital modes, scanners and SDR radio - Page 1
Forum section: electronics / rf-microwave

author: WaveyDipole
author_rank: Frequent Contributor
timestamp: February 16, 2019, 07:50:44 pm
content: Please forgive my newbie questions and the rather long post. I am fairly new to SDR and particularly the new digital transmission standards such as DMR and D-star. First a bit of background. I had been thinking of purchasing a scanner, e.g. AOR8200D, but it seems that everything is going digital these days including ham transmissions. It seems it is necessary to consider DMR and D-Star and other digital standards. There are not many handheld scanners that can do both analog and digital and those that do very expensive indeed. As usually there is the issue of support for various standards by manufacturers and usually at least one or two are omitted. I initially figured that a secondhand analog scanner like AOR8200D would be worth considering, but in light of the digital revolution I have been persuaded to look at Digital devices such as the AOR DV1 or DV10, however, these well out of my budget. The Uniden Bearcat 3600XLT was a possible consideration but this has significant frequency gaps.Rather than paying a lot of money for a scanner, I decided to buy a used SDRplay RSP 2 SDR radio to allow me to scan the bands, experiment and determine whether there are ang signals of interest in my area. If so, then I might go on to invest in actual hardware for the appropriate band.While waiting for it to arrive, I am experimenting with an RTLSDR, but with little success and some confusion. The RTLSDR seems to be a few 10s of kHz off frequency which does not help matters. I am hoping that the SDRplay will be more accurate and provide better performance but in the meantime I am trying to make do while experimenting with various software.For example, I tried setting up GQRX with DSD+ on Linux and manually tuning to those frequencies (or thereabouts, i.e. the nearest signal peaks) but I couldn't get any sound out of DSD+ on any signals that I tuned in. Since I am completely new to this I am likely doing something wrong, needing a better antenna that supplied or my longwire or the RTLSDR is just too noisy. I'm not sure. Setting this up on Linux is known to be a bit of a pig anyway and could be part of the problem, so I am looking to maybe try something out on Windows 7?I would like to know how to determine what DMR or D-Star channels should be available in my vicinity? I did find that there is a DMR repeater about 10 miles away in Markfield on (https://www.ukrepeater.net/dmr.htm|), but I couldn't pick anything up on the frequencies that were associated with it.Whatever the case I would like to ask for a bit of help. I tried registering on the DMR Users UK form, but that requires a callsign, which I do not have. I also tried the UK Radio Scanning Forum, but my browser is completely blocking the connection for security reasons. I am hoping that I can find some help to get started on here.....I have invested in a book called Software Defined Radio by Andrew Barron ZL3DW which I am hoping will prove useful but I was hoping to find some useful online resources.Other questions I have include:1. Are there any good DMR/Dstart/TETRA decoder programs that can be used with an SDR radio?2. Is there a scanner program that can emulate an air-band scanner for an SDR radio?3. What about TETRA? Is there anything of interest to be picked up on TETRA in the UK, or is everything encrypted? (Curiously the only scanner that I am aware that can pick this up is the new AOR DV1 or DV10 handheld. The handheld is *very* expensive for a scanner and the only review I could find says it is a very poor performer and should be avoided.) I was wondering whether I would be able to pick up anything interesting on the SDR radio or is it all encrypted? I ask because I tried compiling telive, but ran into difficulty. if there is indeed nothing of interest then it may not be worth investing any further effort to compile this.3. If I need to purchase a discone, what should I go for. Should I go for a single or double? I have seen references that suggest a double discone is a bit of a gimmick and may actually perform worse the a single one? Is this so? Furthermore, should the discone have the top vertical element or not? So do, some don't. All are quoted to have similar wideband coverage, some comments suggest that the vertical element impedes performance?Sorry, its a long post with lots of questions but I hope someone can help.If this is OT for this form, then please could someone direct me to where I might get some newbie help?

author: testpoint1
author_rank: Frequent Contributor
timestamp: February 17, 2019, 02:52:38 am
content: if you want to decode Tetra, you may buy a professional scanner for that, just like Pctel IBflex, try to ebay find

author: radiolistener
author_rank: Super Contributor
timestamp: February 17, 2019, 07:58:59 am
content: SDRPlay is better than RTLSDR, but not so much.There are also several kind of RTLSDR - original (blue stick), RTLSDR blog V3 (silver stick) and other clones. Original and RTLSDR v3 are worth of money, other is just cheap clones. Original blue stick has better sensitivity, but high temperature instability. RTLSDR v3 has TCXO to eleminate temperature instability and some LPF on the input, but it has slightly worse sensitivity. But be aware, there are also a lot of fake clones for blue stick and RTLSDR v3 stick!Also you should note that RTLSDR sticks works from 24 MHZ, they don't works at lower frequency. There is workaround for that, to use direct sampling (which is already implemented in RTLSDR v3) but it has side effect, because ADC works on 28 MHz, so you will receive 0-14 MHz and 14-28 MHz bands merged together (due to aliases). So, it's better to use upconverter instead of direct sampling.The key parameter for SDR radio is dynamic range. If you want to listen for shortwave, the dynamic range is even more important. But high dynamic range is very hard to get with wide range. So, you should decide which frequency is more important for you. And your better choice will depends on that. If you're interested in 0-50 MHz, you will need short wave SDR. If you are ok to not be able to listen frequencies lower than 50 MHz, but 100+ MHz is important for you, then you will need other kind of SDR (they are cheaper, because don't need high dynamic range). In the last case RTLSDR very nice solution and you will not get very significant improvement with more expensive receivers.

author: WaveyDipole
author_rank: Frequent Contributor
timestamp: February 23, 2019, 02:59:17 pm
content: Quote from: testpoint1 on February 17, 2019, 02:52:38 amAt those kind of prices they are hardly affordable for an enthusiast. I was thinking more like maybe an AOR DV10 or maybe DV1 base, but even these are very expensive indeed and apparently have problems and would be hard to justify buying.https://www.aoruk.co.uk/aor-ar-dv10-review/Quote from: radiolistener on February 17, 2019, 07:58:59 amI don't know whether your experience was with an RSP1 or RSP2, now that my RSP2 has arrived and I have had a chance to play with it, I find it is rather more sensitive and has a lower noise floor then the RTLSDR. It also has antenna and filtering options not present on the RTLSDR. I think it was a worthwhile upgrade. Its also pretty good on HF and without requiring any mods. Whether it is much better on VHF and UHF bands I have yet to prove. I need a decent VHF/UHF antenna first.Quote from: radiolistener on February 17, 2019, 07:58:59 amI have the a version 2, the one that came in a blue aluminium box with the Dolpin on it. It has a 'UV' andf 'HF' antenna connection (I presume 'UV' is a combo of UHF/VHF). Despite that, the HF side was not connected up. There was some circuitry on the host board, but it was not linked to the dongle board. It needed to wind a Tx and do some further modification to complete the direct sampling mod you mention. It worked but I was not terribly impressed with it. There were lots of images and the reception was noisy. I was forewarned so this did not come as a surprise, bearing in mind that it was a $20 gadget.Quote from: radiolistener on February 17, 2019, 07:58:59 amThank you. This partly guided my decision to buy the RSP2. I am indeed interested in HF and even VLF. The RSP2 goes down to 1khz. It doesn't range anywhere near as hight as 6GHz like the HackRF, but it is adequate for what I required.

author: radiolistener
author_rank: Super Contributor
timestamp: February 23, 2019, 03:44:27 pm
content: Quote from: WaveyDipole on February 23, 2019, 02:59:17 pmYes, RSP2 uses 10 bit ADC (MSi2500), which is better for short wave than HackRF which uses 8 bit ADC (MAX5864). Both devices running ADC at similar speed, so there is no advantage from decimation and we can compare them by native ADC bits. And RSP2 is winner in that comparison.But RSP2 also has some bandpass filters for short wave and it makes it even better for shortwave than HackRF.