Saturday, 9 June 2018

950MHz 2G Spectrum

Here are some spectrum views of the 900MHz GSM phone band, captured with a SDRPlay RSP-1 and a 1/4 wave ground plane next to an upstairs window (looking north).
My Comet GP-15 tribander on the chimney, with over 25m of coax gave roughly the same signal for a mast which was line of site except for a few trees (the sector facing me is on 959.4). A mast only a few streets away with my best sector on 953.8 was much better on the GP-15 (about 15dB), it's on the opposite side of the house.
Vodafone using 951.4 - 954.8 (18x 200KHz channels 82-99), O2 using 955.2 - 959.8 (24x 200KHz channels 101-124). Most sites are now Vodafone and O2 into the same antennas. It looks like a lot of the newer sites which were built for 3G coverage (usually roadside poles) have been fitted with 2G 900MHz. 2G GSM is nowhere near finished yet in the UK, the cheapest phones are 2G only, and as the turnover of smartphones is faster, support for devices without 4G could be cut down to 2G voice/texts only before too long. 3G capacity is already being cut by refarming the 2100MHz band to 4G for up to 2/3 of the bandwidth. 2G GSM is used by a lot of remote control and slow data applications too, things like tracking devices, digital signage where the speed of sending a txt or GPRS data doesn't matter.
I'm not sure what's happening with the channels like 955.8MHz where the signal isn't continuous, seems to be an extra channel from the same sites.






Monday, 28 May 2018

FT-8900 Programming Errors

50MHz FT8 was full of stations today around 50.313, all over Europe. Also I had a go on 24MHz with my random bit of wire and 10 watts, made some contacts into Germany and the Netherlands, also received by 2 stations in the UK in the Bournemouth (M1HHL) and Medway (M0OLA) area.

Today I went to the car and connected up my laptop to the FT-8900 to download a new set of memories to it. Using the FTB8900 software as usual, I started off with an upload of the existing settings, and everything was OK. Then when doing the download, it got to the end and then the radio displayed 'clone error' and the software displayed an error message saying it did not receive the final confirmation from the FT-8900.
I was using one of the very cheap USB to serial adaptors which I bought last year, instead of my usual Prolific chip based adaptor (fake chip so need to use an old driver). These new adaptors use a CH340 chip (never heard of it until I plugged one in, expecting a Prolific chip) instead, drivers aren't included with Windows 10.
Well the failed download completely reset the radio, clearing all the memories and other settings. I tried again later, after the temperature had dropped a bit - when I was trying to get the radio to program earlier the car was showing the temperature as 27C and not very comfortable sitting there with a laptop. With the old Prolific adaptor the download worked OK.
I've had trouble with the CH340 cables before, with the WSJT-X software, I had to increase the CAT polling interval from 1 to 2 seconds on a Yaesu FT-847 otherwise it would sometimes get CAT errors.

Downloading to radio - this time it worked

Bargain basement USB-serial adaptor with CH340 chip

Good old Prolific USB-serial, bought at Llandudno Maplin a few years ago

USB device details for the USB-serial adaptors


Thursday, 15 March 2018

FT8 - 4 Weeks On

I've been using 144MHz FT8 for about a month now, and it's getting more popular. I've been leaving the radio on 144.174 all day while I've been out, and operating remotely using TeamViewer on my phone.
There must be quite a few people doing the same as if I call CQ at any time of day, someone will have received me and there's a spot on PSK Reporter. Because of the extra range of FT8, there's more activity on there now than on 2m FM. Some days I'll put a CQ call out and not get a reply, but it's not a waste of time as I could have been received by someone new.
At the moment conditions on the HF bands aren't very good above 10MHz so it's good that there's something else to do with an SSB radio.

I put a CPC order in today for a few bits and pieces, and ordered some coax adaptors on AliExpress. AliExpress is usually pretty slow (a month or more) but that means it's a nice surprise when something turns up after you've forgotten all about it. One of the things in the CPC order was a dishwasher cutlery basket, but all the others were more electronics related. Ordered 2 optical audio cables as I'd used one for connecting up a sound bar then realised I didn't have any more to connect my PC up to the amplifier.
With CPC, I tend not to use the website to search or browse through the products because the cheapest of anything is usually in the paper catalogue updates I get through my door, or in the PDFs on the website. Most popular things are in the catalogue update, and I like catalogues, it's sometimes better to have a look through pages with pictures and things ordered nicely, rather than a list of search results.

Thursday, 22 February 2018

VHF FT8

After reading on Twitter that some people were trying the very popular FT8 data mode on 144MHz, I had a go. I don't have anything like a VHF DX station at home, with just a Comet GP15 vertical on the chimney, fed with a bit too much coax.
The frequency for 2m FT8 is 144.174.
I started off using my new SDRPlay receiver and found that I was able to decode a few stations, outside my usual VHF range (G4KUX in IO94 and GM4FVM in IO85).
After connecting up a transceiver, I was able to make some 2-way contacts at this distance, and was even getting reception reports of my signal via PSK Reporter from up to around 300km. This makes the 2m band a bit more interesting, and because data modes software like WSJT-X automatically sends reports to PSK Reporter, even if I'm away from the radio, it's still worth leaving it on all day just in case someone calls CQ.
At the moment, there aren't really any 'lift' conditions on 144MHz, at least not which you would hear if listening to FM or even SSB, and most of the long distance propagation is from reflections off aircraft. Reflections off fast moving objects like aircraft shift the frequency from the doppler effect, and it can be over 100Hz. With FT8, the bandwidth is very narrow, so if there are multiple paths, the same signal can appear on 2 different frequencies. See below for some FT8 activity where there are multiple decodes.

On some days I've received 10 different stations on 144MHz FT8.


Saturday, 3 February 2018

Because I Hadn't Posted Anything Since Last Year


Happy New Year 2018


 USB load - switchable between 1 and 2 amps

 Barrow BBC MF/DAB broadcast site, is the colinear lower down the mast for smart metering because nothing else is from the site ?

Majority Huntingdon DAB/FM/CD system

New drill

Thursday, 7 December 2017

Saturday, 28 October 2017

More UHF APRS Testing

I tried the E32-TTL 1 watt 70cm LORA module a bit further away from home, again using APRS software to send the position to the internet.
The location I tried first was some high ground just off the A65 to the west of Settle (grid reference somewhere around SD786669) on the narrow road above the Austwick TV mast. This has a good take off towards the west.
Instead of the mobile antenna I put a short antenna directly on top of the module and taped the thing to a mop handle so it could be as high as possible while operating. This also gets rid of any coax cable loss.

 Video camera also fixed to mop handle

 View to the west from near Settle


 But did it work? Yes it did, at a distance of 37.7 miles (60.7km), with more than one transmission being received as I moved around the parking area.
I tried another two locations further south, which weren't on high ground, but received nothing. These were at the Lancaster (Forton) M6 motorway service area and just outside the boundary of the Charnock Richard M6 motorway service area.

My next experiment was to compare the performance of the LORA module against normal 1200 baud packet radio using an FM mobile transceiver.
Using the same antenna as in my last blog post (it's a small Moonraker dual bander, about 40cm long, on a mag mount), I transmitted APRS beacon messages from my Yaesu FT-8900 on its 20 watt setting. The frequency was the same as I had used for the LORA test.


See the results of the LORA test below


Result? A lot worse than the 1 watt LORA transmissions. Because the car APRS tracker has no logging function, I could only guess where any failed transmissions were from. I know that it beacons every 110 seconds so I've put red Xs in rough locations of where it should have worked but didn't.
The blue O shows where it actually worked but no location was sent (my tracker is programmed to send some other information every few beacons instead of the location). I had stopped the car there, which would have helped as I wouldn't have been passing through any multipath dead spots while transmitting.
So with 13dB (20x) more power on the same frequency, traditional packet radio is still worse than LORA when used mobile. Even if you compared VHF packet with UHF LORA, I don't think 20 watts VHF (to a 0dB gain antenna like the Moonraker) would get much further than 1 watt UHF.

And here is Dales Radio's Ingleton antenna (103.0 MHz), covering the area further west of Settle, with Settle itself on 104.9 MHz.