Sunday, 16 March 2014

BladeRF, the transverter and HF TRX; it's been there all the time!

BladeRF, the XB-200 transverter and HF TRX; it's been there all the time!

The BladeRF and now its XB-200 transverter are very neat pieces of gear. Now the big "but" or "however".

Many people have been wanting to use the BladeRF on HF and were waiting for the transverter to be delivered in anticipation of it covering HF. However, the original range of the transverter was 30 to 300 MHz, with no apparent coverage. When the final design and photos were released, coverage was 60 kHz to 300 MHz, which no doubt pleased many people.

I went though the schematics trying to find the modifications to cover HF, but they were not apparent, a point I raised in the Nuand forum. I received a reply from Nuand to say that the HF access was not very obvious and went to the ADC/DAC. This mystified me for a few days until it finally clicked on how HF is done, which is exactly what they way they said. However HF TRX is virtually independent of the transverter and could have been used with just the BladeRF with some extra circuitry, that is still probably needed.

HF TRX is possible with the BladeRF because of the design of the main TRX chip, the LMS6002D. Its block diagram is shown below:

The chip is a superhet TRX that uses a local oscillator to mix 300 -3000 MHz down to baseband then through the ADC/DAC. The main signal path for the receiver is in at pins RXIN1-3, mix down to baseband, through the ADC and out via RX_IQ_SEL and RXD(11:0) 12 bit bus for digital processing. The transverter adds to this by up-mixing 300 - 300 MHz to a 948-1218 MHZ and through the normal signal path. All reasonable, but what about HF?

HF TRX is achieved by bypassing the most of the LMS6002D circuits and going straight to the ADC or DAC via pins RXOUTI/Q and TXINI/Q. As such the RX samples directly via the ADC at for HF. These pins are accessible on the BladeRF. The transverter just adds a balun and connector, shown on the last page of the transverter schematics and not mentioned in the block diagram.

The PWR_HDR6/PWR HDR6  connectors J5 and J6 on the transverter board connect to PWR_HDR6/PWR HDR6 connectors J60 and J61 on the BladeRF.

There is nothing wrong with this approach as many SDRs are based on inputs/outputs directly to ADC/DACs. It how the new Red Papaya ( and see my other posts)(14 bit 125 Msps ADC/DAC) could be used as a very capable HF TRX. However, for the BladeRF on HF there are a few consequences.
First, the software to drive the HF part of the BladeRF will be different to that for the 30 - 3000 MHz, assuming the transverter can be essentially invisible via firmware.

Second, the HF parts may need extra circuitry such as a low-pass filter and a RF amplifier.

Third, the actual coverage of the ADC/DAC would seem to be limited a maximum of 20 MHz, half the sampling rate of the ADC/DAC of 40 Msps. It is possible for the transverter to go down to 20 MHz but there is a high-pass filter and the local oscillator/images may cause issues.

In conclusion, none of this is intended to be a criticism of the BladeRF and its transverter; I look forward to receiving my transverter and am already impressed with BladeRF's capabilities. It is intended to point out that HF coverage is done quite differently to the main 30 - 3000 MHz coverage, necessitating a few changes in hardware and software.
However, while the Red Pitaya is primarily for software-defined instrumentation, it may be a better hardware platform than the BladeRF for a HF SDR TRX, particularly with its much higher sampling rate, 125 vs 40 Msps? Each to their own?

Monday, 10 March 2014

Red Pitaya: arrived and working

Red Pitaya: arrived and working

My Red Pitaya has arrived and was working with a minimum of fuss. Simply type in the device's unique MAC address on the connect page and hit connect.

The instrument functions are web applications. Just click which instrument you want and it comes up in a web page. I was curious how they could get it to work on any computer, tablet or operating system, but the web access is the answer. I am not sure what consequences that has for performance, but it works and it is still early days.

The Red Pipaya connected to give some idea of size. It gets pretty hot, maybe too hot for a warm climate like northern Australia; we shall see. The device is working as an oscilloscope and signal generator, with an output connected to an input.

A sine wave at 20 MHz. Many of the adjustments are manual and take a bit of getting used to. However, it works. Not the cleanest sine wave; not sure if it is the signal generator or oscilloscope. Latter I will check with my dedicated oscilloscope to see.

Occasionally it throughs up an error when changing settings. Could be caused by anything; I am using Internet Explorer on Windows 8.1. I hit "ignore" and try again until it works. It doesn't freeze, just throughs error messages; again, early days for the hardware and software.

Next is the spectrum analyser. Back to the applications webpage and select the new instrument.

The two channel spectrum analyser seems to do a fixed sweep from DC to 65 MHz, with the ability to zoom into a smaller bandwidth for the spectrum. However the waterfalls stay fixed at full bandwidth, which is not that useful. Again early days.

With some modification, the device would work as a panadaptor on the first IF of some transceivers, as long as the frequency is below 62.5 MHz. Unfortunately my ICOM IC-7410 has a first IF at a few MHz higher.

The spectrum analyser is a start to being a Software Defined Radio SDR. With the right software, it has the makings of a very good HF SDR TRX!

The Red Pitaya can de driven in terminal mode. I haven't tried that, but will investigate.

In summary, an awesome device with lots of potential. A very novel interface that allows its use with almost any form of computer, as long as it can run a web browser. The odd bug or limitation, but it is early days. I will be watching their site to see how things develop. They made a big effort to deliver on time. There are a couple of other instruments due in a few weeks, that didn't quite make the initial release. Very professional job and bodes well for the future.

Friday, 7 March 2014

HiDes CCHDTV camera and DVB-T modulator DC-100 Full HD 1080P

HiDes CCHDTV camera and DVB-T modulator DC-100 (preliminary)

I received a HiDes DC-100 (US$250 for camera, $100 for lens) last week but did not have much time to set it up, other than to verify it works.

With a bit more time tonight I have a very nice Full HD image from it.

The lighting was bad, but a still a good clear image. The DC-100 transmits both a SD and HD channels as can be seen in the channel list. The camera is running on its default setting of 177 MHz, 6 MHz bandwidth, but over a cable with an attenuator. The image is 1080P 30 FPS. As a result there is some flicker from the 50 Hz lights.

I will put up some photos of the device and its internals later.

CCHDTV is an emerging standard of DVB-T cameras designed to run on existing coaxial systems in buildings and institutions. The devices all seem to be based on the ITE modulator chips. Google CCHDTV for more information.

The DC-100 uses a standard CCTV SDI camera, either 2 or 5 Megapixel, the converts the raw SDI stream to DVB-T with one of HiDes modulators using the ITE chips.

The DC-100 does not come with audio, as it is usually not permitted for CCTV. However HiDes have a mono audio card to allow its use for amateur DATV.

The DC-100 can be program for channel by two rotary switches at the back and band-width (6,7,8 MHz; which only suits some countries, like Australia). It is possible to change firmware via a micro SD card and all TX properties via some extra hardware through the return channel. It is on it's way.

The camera uses CS mount lenses, so it is possible to use good quality lenses.

All in all, the simplest and best quality way to do Full HD DVB-T DATV. Add some amplifiers and decent antenna and it makes a nice system.

I am more interested in the small signal side of DATV, picture quality, production software and the like.

More later.