Monday, 2 April 2018

DIY 2m single connector pass reject coupling

DIY 2m single connector pass-reject coupling

Introduction

In my last post I describe the repair and tuning of a high performance 2 m duplexer that uses an unusual single connector pass-reject coupling. In this post I describe how to make one for about $30 that achieves the same level of performance.

First, I explain what seems to be the theory of the pass-reject coupling as a parallel tuned circuit, using the coax as the inductor and part of the capacitor. The coax conductor is the other part. The variable piston capacitor is in parallel with the coax capacitor to allow tuning. It also gives the necessary mirroring for RX and TX responses.

Then I describe how I made one that achieves about the same performance as the original.

I am very pleased as I have been working on DIY pass-reject couplers for some time. It allows the construction of a complete high performance, six cavity VHF duplexer for about $300, less the cost of connectors and cabling.

Theory of the tuned coupling 

The coupling is a pass-reject type using a parallel tuned circuit, DC from coax connector to earth. Looking at the centre pin, it is connected to the shield of the coax and the conductor is earthed, then the coax is bent into the coupling shape. At the other end, the shield is not terminated but the the conductor is connected to earth. This is a tuned circuit, with the shield both an inductor and part of a capacitor. The capacitor is from the capacitance of the coax at 98 pF per metre. The piston capacitor (1-10 pF) is in parallel with the coupling capacitance, allowing tuning.

The coupling is similar, but the reverse of a magnetic loop antenna. In a magnetic loop antenna, the antenna loop is the tuned circuit and the coupling an un-tuned loop to couple the RX/TX coax to the tuned loop; a transformer. In the cavity filter, both the resonator and coupling are tuned, explaining the pass and the reject. The resonator determines the pass frequency and the coupling the reject frequency, which is how they are tuned. Resonator first for the pass, then the capacitor reject.

The TX coupling is shorter and tunes to a higher frequency, not clear why.

The mirroring comes from the adjustment of the trimmer. more gives RX shape, pass then reject, whereas less gives the TX shape, reject then pass. Not sure why this occurs, some interaction with the resonator I suppose.

The Q of the resonator, cavity and coupling determines the depth of the notch. The Q is high, in the order of 2000 to 5000.

The base of the resonator, effectively a quarter-wave antenna is primarily a magnetic field, whereas the other end, electrical. Being near the base, the coupling is magnetic, as per an air-cored transformer.

Pass-reject couplings are particularly good as they give high out of band rejection as well very sharp pass and reject for RX and TX.

Effective circuit, ignoring resistances.


Process

As with other coupling construction, as I have describe a careful drawing is made of the commercial coupling on grid paper. In this case, I just drew the outline with the coupling sitting flat on the paper. The coax sizes are drawn too big, but my coupling just needs to fit inside the drawing.

The first photo shows my copy and the commercial coupling, the second, the paper tracing.



Materials

The biggest problem was getting a minimum 32 mm disk for the base of the coupling. I couldn't think of how to make them; the hole is not in the middle. Then I thought of getting them made on a lathe; expensive. But then I thought laterally. The first was to use large coins that could be soldered. The 1966 Australian 50 cents is 32 x 2 mm and 80% silver; so I ordered some at $10 each. Then I tried searching eBay; stamped brass blanks were available locally at about $1 each; a bit thin at 1.2 mm but 32 mm diameter is ok. They arrived first and I used them.

The coax is semi-rigid RG402 copper tube shied, PTFE and silver/copper/steel inner, available from Element 14 at $20 per m.

I had some piston capistors. They are available on eBay from "element 13" in Bulgaria, or from usual suppliers at high prices. 1-14 pF is ok.

Making

The holes are drilled with a step bit in a drill press. A Dremel or similar is useful for cutting/sanding/stripping.

I extended the centre pin by slipping on a piece of the coax shield to give more length. Bending the coax is easy with the right diameter dowel. Soldered the coax to the pin, cut the other end to length soldered it to the capacitor and pin again.

Tuning

Checked it would tune to the same frequency as the original and tried it in the cavity; top wasn't perfect fit but it is to go into another cavity anyway. Very close to the original in performance, even with the 1600 MHz split; excellent.

Original coupling

 

Copy; near identical. Low loss and high reject.

Mirroring from adjusting the trimmer capacitor



Free air resonance


Conclusion

After many attempts at an easy to build pass-reject coupling, finally success. The couplings are for a fairly big tuning range, so dimensions are not too critical.

I will build a copy of the shorter TX coupling and see if it performs in a similar manner. To a point, the one I have made can act as RX or TX by adjusting the trimmer.







Wednesday, 21 March 2018

2m Duplexer unusual design repair tune pager-reject

2m Duplexer design repair tune pager-reject

Introduction

My local radio club's main 2m duplexer had an intermittent fault. The duplexer was fixed and retuned to a new channel, 1600, not 600 kHz split, partly to move the RX further from a Pager TX.

The Telewave TPRD-1556 Pass-Reject duplexer has an unusual coupler that I had not seen before that works very well, 45 db reject each. They should be possible to DIY. The fault was a defective piston capacitor used to tune a cavity.

An unexpected benefit of the pass-reject RX cavities is a significant 72 db reject of the 148 MHz pager TX. More is possible, if needed from notch cavities at 25 db reject each.

Tuning high performance cavities, 45 db each, highlights the limitations in instrumentation, particularly the dynamic range, 85 db, with the reject response lost in the noise floor.

Design of the Telewave TPRD-1556 Pass-Reject duplexer 

The Telewave TPRD-1556 Pass-Reject duplexer looks like any other six cavity pass-reject duplexer, except that the cavities only have one coax connector not two.

The mystery is in the design of the coupler. The coupler use semi-rigid coax as capacitors as well as the main part of the coupling. There is a piston capacitor to adjust the spread. The design allows a spread from 400 kHz to over 1600kHz, whereas another conventional pass-reject cavity could only go out to 1100 kHz spread.

The couplings are different lengths in order to mirror the RX-TX responses, something that can be difficult to do. I don't know how the do it, presumably with phasing.

Telewave TPRD-1556 Pass-Reject duplexer


RX coupler and detail; ~150 mm long

RX coupler detail showing one end of the centre conductor connected to the coax connector pin but the other earthed. One end of the shield is connected to the capacitor and the other end is connected to the centre pin

TX coupler; ~ 130 mm long

Repair- intermittent piston capacitor

The piston capacitor, while quite reliable, had failed as the ceramic was loose in one end.

Fixing it was simple. It was not possible to just unsolder the capacitor as that would disturb the coupling. I removed the inner piece, then using bolt cutters, crushed the ceramic. Then the bottom portion could be unsoldered and the top part removed. I only had a shorter, smaller value capacitor, but as the screw of the original was most of the way out, I thought it would work, as it did.

New capacitor and original one, showing construction with concentric cylinders.

Tuning the duplexer

Tuning is straight forward with a spectrum analyser and tracking generator. Repeater RX 145.6 MHz, TX 147, 1600 kHz split. The cavities are done one at a time. The length of the resonator is set first and shouldn't need to be readjusted. The spread is then adjusted. The cavities work very well giving 45 db reject and less than 0.5 db loss; within specification per data sheet.

Having done all of one side, I then join two, check, then join the third. The photo shows two cavities, with the reject a bit lost in the noise. The reject should be 90 db, but the analysers dynamic range is only about 85 db. The second photo in each pair is the SWR for three cavities; not sure were the second dip comes in the RX chain, but of no consequence. Between the pairs, the mirroring can be seen.

Two RX cavities showing TX reject, better than 85 db.


SWR of three RX cavities, odd second dip.

Two TX cavities showing RX reject, better than 85 db.

SWR of three TX cavities

Pager TX rejection

The repeater site is near two 2 kW pagers at about 148 MHz. There was a major concern for desensing the repeater's RX. Fortuitously, the club had this faulty pass-reject duplexer that could be fixed and retuned for the site.

An unexpected outcome is that the pass-reject duplexer has about 72 db reject on RX and similar for TX. This can be supplemented by notch filters on the pager frequency to give a further 25 db reject for each cavity, if necessary.

Perhaps obvious, but I was not aware of the potential for pass-reject duplexers to attenuate unwanted signals other than the desired RX and TX for the repeater. This is a significant advantage over other designs, such as notch cavities that reject either RX or TX, but let everything else through.

The repeater's licensed split was changed from the standard 600 kHz to 1600 kHz to further separate the the RX and pager. Ironically, the pager rejection for be 600 kHz split would be 20 db or more, the reject being in the noise and outside the spectrum analyser's dynamic range of about 85 db.

I will report more on this when the repeater is installed. I will probably do another post on this subject as it is an important topic, but incidental to the main purpose of this post.

148 MHz pager rejection for RX 145.6 MHz, 72 db with pass-reject duplexer

Home-made pass-reject cavity filters

I had been experimenting with notch filters for home-made duplexers, very easy to make, whereas I will now try to make pass-reject couplings based on those used in this duplexer. They are particularly good in that they use a single connector , simplifying construction. They seem to be out of patent and should not be a problem copying them, not that I want to sell any. More in another post.

Limitations of instrumentation tuning pass-reject duplexers

Tuning duplexers highlights the limitations in instrumentation, particularly dynamic range. Each cavity has about 45 db reject. Two give about 90 db reject, but the instrument shows noise at the reject frequency, indicating it is outside the instruments dynamic range. All three cavities give about 135 db reject, way down in the noise.

The response can be improved a little using a low resolution band width (RBW), 1 kHz in the last photo. But it takes some time to plot a 10 MHz span at 1 kHz and is only useful for static devices.

I use a Siglent SSA3021X spectrum analyser, a "cheap" Chinese instrument and it has about 85 db of dynamic range. Name-brand ones do maybe 10 db better; not a lot. The specification of the instruments give the noise floor, about 150 db, but don't give the dynamic range. The dynamic range is largely determined by the analogue to digital converter (ADC).

One way of checking the TX reject at the RX is to use the repeater's TX, with the antenna port connected to a dummy load, and measure TX reject signal at the RX port. It is prudent to use a cheap power meter and a variable attenuator to first check that the signal is low enough. The spectrum analyser can then be connected to the RX port and the TX leakage measured; notionally 145 db down on TX output. To a point, the check needs to be done as the repeater's RX is to be connected to the port. The TX reject signal is more indicative than accurate as there can be stray RF from leaky cables and enclosures. Test leads and the repeater cables should be double shielded coax to minimise this.

The other check is the TX output of the repeater and through the duplexer to make sure losses are within expected losses.

I will do another post on this subject as it is important and include some work with wide-band software-defined radios (SDRs) as real-time improvised spectrum analysers.

 





Friday, 26 January 2018

High power UHF DVB-T amplifier, filters and testing

High power UHF DVB-T amplifier, filters and testing- very draft


I have a used 150 W pallet amplifier from a scrapped DVB-T transmitter via eBay. It is bolted to a heat sink from a satellite transmitter.



I am basically following the 1 kW CW UHF amplifier from W6PQL. I have the low pass filter for the amplifier. I temporarily soldered some SMA connectors to test its frequency response. Down about 1 db at 500 MHz, but -40 db at the third harmonic; very good.




It has been suggested to use a pass band cavity filter duplexer. I had one on hand that I had just tuned for a repeater, trying to get a narrow pass-band.

Just using three cavities, I varied two of the three cavities to try to get a wider response. No joy, little wider, but more importantly 10 db loss.




To be continued...

Monday, 15 January 2018

Polyphase harmonic rejection mixer: AirSpy HF+

Polyphase harmonic rejection mixer: AirSpy HF+

Introduction

Can you get excited about a new mixer, usually boring devices that haven't changed in decades? Yes, the new polyphase harmonic rejection mixer in the AirSpy HF+ is almost as revolutionary as SDRs and will have a major influence on their design.

The big advantage of a polyphase harmonic rejection mixer is that it acts as a RF filter for the selected signal, as well as suppressing harmonics and other aliases of the mixing process and local oscillator. It means that the mixer can virtually be connected to the antenna. Typically, a polyphase harmonic rejection mixer converts down to an ADC at base-band. It seems they can be used for both RX and TX.

The post covers how the AirSpy HF+ works, and gives references to what I have been able to find out about polyphase harmonic rejection mixers. They are new and still covered by recent patents. A link to a PowerPoint gives general technical details of the mixer.

AirSpy HF+

The AirSpy HF+ is rather unique for modern SDRs as its main purpose is to cover the HF bands, although it does cover VHF as well, although it only covers 200 kHz. And costs just $199. Most new SDRs start at VHF and go to daylight, well 3 or 6 GHz! They are intended for wide band mobile phone type applications, with coverage up to 30 MHz. The new LimeSDR (and $99 mini) and transverter ($299) covers up to about 10 GHz, but has limited RF band-pass filtering.

The unassuming appearance of the HF+ is shown in Picture 1 and the basic architecture of the HF+ is shown in Picture 2, clipped from https://airspy.com/airspy-hf-plus/.

Picture 1 AirSpy HF+

Its maker's description: "Airspy HF+ achieves excellent HF performance by means of a low-loss preselection filter, high linearity LNA, high linearity tunable RF filter, a polyphase harmonic rejection (HR) mixer that rejects up to the 21st harmonic and multi-stage analog and digital IF filtering.

The 6 dB-stepped AGC gain is fully controlled by the software running in the DSP which optimizes the gain distribution in real time for optimal sensitivity and linearity. Harmonic rejection is a key issue in wide band HF receivers because of the large input signal bandwidth of the input signal. The output of the IF-filter is then digitalized by a high dynamic range sigma delta IF ADC for further signal processing in the digital domain."

Picture 2 The basic architecture of the HF+


Polyphase harmonic rejection mixer

The way the new mixer works is not simple, it uses multiple phases (16?) of the local oscillator to use phasing to reject its harmonics, but at the same time, and because it is to a 200 kHz base-band, it rejects everything else too.

The big advantage is not needing a large number of band pass filters like a direct sampling SDR; the IC-7300 has 15!

The best explanation I have found is a slide show; http://icd.ewi.utwente.nl/temp_files/158b39412cff88a4181bfec0f4449c24.pdf. It is also subject to patent; https://www.google.ch/patents/US20110298521?hl=de. One of the authors wrote the slide show.

The mixer is an analogue CMOS device, STA709 from ST Microsystems, but the full datasheet is currently only available under NDA (non-disclosure agreement). So, no point taking RF cover off the HF+, too hard to remove anyway!

The new mixer is not entirely new, as stated in the patent, it relies on existing harmonic rejection mixers and other patents.

From AirSpy group: "You can see it as a "super Tayloe mixer". The problem with the original Tayloe Mixer is the harmonic responses at multiples of the LO frequency. The fix is to mathematically suppress these responses by adding more phases. The LO will no longer look like a square wave, but rather like a quantized sine wave. Basically, the more phases you add, the more harmonics you cancel.
This method is combined with narrow band filtering at the mixer itself. There is a switched-capacitor N-Path filter built into the mixer that is tuned using the same LO phases, which provides additional selectivity.
When you see it, all the ingredients required to implement this architecture can be implemented using CMOS silicon, and have a very good "horizontal" and "vertical" scalability: Horizontal with more phases (hence, less harmonics); Vertical with better fab processes (better linearity and NF).
The icing on the cake: This same technology can also work for TX."

Performance of AirSpy HF+

The HF+ is still very new, I only received mine in the last couple of weeks. The HF+ gives some performance results. There have been a number of comparative reviews against other SDRs, such as the new $99 RSP1a, by radio amateurs and shortwave listeners. However, there has not been a full technical review by the ARRL or RSGB.

However, with the limited testing the HF+ seems to have a high dynamic range and superior ability with weak signals near large signals, as would be expected from the design.

Conclusion

The polyphase harmonic rejection mixer of the Airspy HF+ is a significant development in radio design and is likely to rival other technologies over the coming years.

Appendix 1

Summary incorporating comments from AirSpy IO Group
Hi All

I asked the Airspy group about the workings of the HF+, and have summarized my own findings and comments from the group:

The HF+ uses a very modern and novel architecture, primarily a polyphase harmonic rejection mixer. See https://airspy.com/airspy-hf-plus/

As best I can work out, when converting to base-band, it is an effective filter for the desired signal and rejects even strong signals close by with virtually no filtering ahead of the mixer.
 
It uses multiple (16?) phases of the local oscillator to use phasing to reject its harmonics, but at the same time, and because it is to a 200 kHz base-band, it rejects everything else too. A bit like the old phasing SSB modulators, that used two phases.
 
The big advantage is not needing a large number of band pass filters like a direct sampling SDR; the IC-7300 has 15!
 
The best explanation I have found is a slide show;  icd.ewi.utwente.nl/publications/get_file.php?pub_id=563. It is also subject to patent; https://www.google.ch/patents/US20110298521?hl=de. One of the authors wrote the slide show.

From AirSpy group: "You can see it as a "super Tayloe mixer". The problem with the original Tayloe Mixer is the harmonic responses at multiples of the LO frequency. The fix is to mathematically suppress these responses by adding more phases. The LO will no longer look like a square wave, but rather like a quantized sine wave. Basically, the more phases you add, the more harmonics you cancel.
This method is combined with narrow band filtering at the mixer itself. There is a switched-capacitor N-Path filter built into the mixer that is tuned using the same LO phases, which provides additional selectivity.
When you see it, all the ingredients required to implement this architecture can be implemented using CMOS silicon, and have a very good "horizontal" and "vertical" scalability: Horizontal with more phases (hence, less harmonics); Vertical with better fab processes (better linearity and NF).
The icing on the cake: This same technology can also work for TX."
 
Apparently the mixer is a CMOS device, STA709, but the full datasheet is currently only available under NDA. So, no point taking RF cover off the HF+, too hard to remove anyway!
 
Regards Drew VK4ZXI




Friday, 5 January 2018

Modifying cavity filters for DATV TX or for repeaters

Modifying cavity filters for DATV TX or for repeaters

Introduction

I am currently doing further work on using notch cavity filters for DATV DVB-T transmitters. My earlier efforts were with what I had at hand and not knowing the solution; I (re)discovered that notch filters clean up DVB-T TX very well. However, it was at low power, 10 W, and high losses, >6 db because of the six cavities in a mobile duplexer. Here, I will report on modifying high power >100 W individual filters. In the next post I will report on using them and determining is just one pair are sufficient. The other goal of this post is to show how easy it is to modify older commercial filters for DATV or repeater use.

Modifying cavity filters

Old commercial filters are relatively easy to modify as the only thing that changes is the coupling loop, provided they are on frequency (not too hard to change that too!). Notch filters are the simplest as they use a single simple coupling, just a loop of metal. Old commercial filters are usually made very well, often silver plated. On UHF, they are relatively cheap; $100 for a four cavity duplexer.

Other than the coupling, the RF design of a cavity filter is simple, a quarter wave resonator (antenna) in a box, usually a cylinder. With a notch filter, the cavity is connected to the TX coax line with a single coax "T". The cavity absorbs the RF at the resonator's resonate frequency; an antenna in a box! The impedance is determined by the ratio of the cylinder to the resonator, like coax, about 3:1 for 50 Ohm.

The mechanical design is more complex, particularly with a variable length resonator to change frequency. The Q should be as high as possible, which is why many are silver plated brass, although can be copper plated or aluminium. The adjustment screw is an non-magnetic, low thermal expansion alloy of steel, Invar, with finger stock for a very good connection to the movable part of the resonator. There are "tricks" with the couplings to get good results without high cost. Some cavities use a capacitive "hat", to change frequency, as is done with antennas.

Couplings are mechanically simple but very complex for RF. There is virtually nothing in textbooks, most of it is proprietary, but most types are covered in: http://www.repeater-builder.com/antenna/pdf/ve2azx-duplexer-info.pdf. Black magic!

The key point of resonators here is that the closer to the resonator, 2-3 mm, the higher the coupling and the deeper the notch. However, as coupling increases, losses increase.

Making modifications

I have made a new coupling for a pair of large aluminium cavities, 150 mm diameter and about 400 mm long. The process of doing it is fairly easy, remove the original coupling, a loop soldered to an N connector. Unsolder the end of the loop attached to the connector pin and cut the earthed end to allow the new coupling to be soldered to it.

Make a sketch of how the coupling is mounted in the cavity and measure all the critical dimensions, particularly the connector center pin to the resonator and the same for the earth point. A small measure can be made by cutting a rectangle of grid paper. Then do a 1:1 drawing of the location. The new notch coupling is about 20 mm parallel to the resonator and 2 or 3 mm from it. The coupling can be made from a strip of copper about 5 mm wide and 1 mm thick, or a larger diameter piece of copper wire. The coupling is bent with a pair of long nosed pliers so that it matches the drawing. See Photo 1 of my drawing.

Once the coupling is accurately bent, solder it to the connector and adjust the shape as needed. The only part that is critical is that the piece of the coupling closest to the resonator must be parallel.

Photo 1 Sketch of new coupling, as described. I was originally going to solder the earth  leg to the coax connector, OK if PTFE, but soldered it to a tag I cut from the old coupling instead. Both arrangements are drawn. The top plate was 10 mm thick, making things a little awkward.

Photo 1.5 The modified loop. The earth is soldered to part of the old coupling rather than to the connector as originally planned. The earth screw is a bit corroded, I should clean it.


With the resonator screwed back in place, its RF response can be shown with spectrum analyser. Spectrum analysers for DATV can be improvised using an SDR and a noise source for about $200 vs >$1500 for a Chinese one (which are very good). See http://vk4zxi.blogspot.com.au/search/label/noise%20source

Photo 2 The response of the new coupling, a sharp asymmetric notch and about 22 db deep with less than 1 db loss. It initially was about 20 db, but bending the coupling closer to the resonator, a small increase was obtained.

Notch filters are limited to about 25 db. For repeater cavities, I would chase that, but it is not that critical for a DATV skirt/splatter filter.

For a DVB-T filter, a sharp rectangular response is desired. Notch filters have it on the high frequency side, but a shallower response on the low frequency side. As a DVB-T signal is a 7 MHz wide rectangle, made up of nearly 8000 carriers, another notch filter is needed on the high frequency side, but the response reversed. This can be done with a quarter wave length cable between the coax T and the cavity.

 For initial DATV testing. I will only do one side, so I can compare it directly with the unfiltered response on the other side of the signal.

Other UHF cavity filters

I bought a four cavity repeater duplexer a couple of days ago that I might use if I need two cavities per side for DVB-T.

I connected up one of the cavities and had a look at how it worked. Wow! An excellent pass reject cavity for a 70 cm amateur repeater. I opened one cavity and was surprised by two things. First that it was copper plated brass (not silver) that was still working well after about 30 years. The second, was how far the coupling loops were from the resonator, >20 mm. This was significant for me as I had struggled with pass reject cavities for 2 m. I tried to put the coupling near the resonator, as per notch cavities, but may have introduced too much induction with long wires. The other problem is when the connectors are opposite each other from the resonator, common with pass-band cavities.

Photo 3 The test one I have been discussing earlier on the right and the old cavity just noted on the left. Size matters for cavity filters as the surface area is proportional to Q, as well as power handling; the bigger the better.

Photo 4 The response of the old pass reject cavity, a huge 50 db! Great for a repeater but no use for a DATV skirt/splatter filter.


Photo 5 The assembled duplexer, a Motorola T1500 series, and unassembled cavity .

Photo 6 A close-up of the resonator and coupling loops, note the large spacing from loop to resonator. It is configured as a pass reject with a variable piston capacitor between coupling loops. May be original but looks like a modification; not mentioned in the 1983 Motorola brochure. Mounting the capacitor can be mechanically difficult as it must be insulated and accessible for adjustment outside.

Photo 7 The pass reject response can be changed to notch, by unsoldering a wire from one coupling loop, then using a coax T on that connector. A very disappointing 10 db because the loop is not closely coupled, being so far from the resonator. The response can be improved by making a new loop that is 2 - 3 db from the resonator, as described in the main article. The cavity can be converted to pass-band by removing both wires and increasing coupling.


Conclusion

It is relatively simple to modify used cavity filters suitable for use as a DATV DVB-T filter. The next step is to set it all up to see how well one high power cavity will work.




Sunday, 24 September 2017

LimeSDR running DATV Express DVB-S TX software

LimeSDR running DATV Express DVB-S TX software (1st draft)

With the MiniTioune DVB-S RX, I have begun trying different TX using DATV Express software under Windows 10. The logical first hardware would be the DATV Express hardware TX, but having shifted rooms in the house, I have not been able to find; I know exactly where it was in the other room!

The LimeSDR is a popular recent SDR dual duplex transceiver by Lime Microsystems using a new version of their own chip. Cost is about US$250, but they have just announced a mini version for about US$150. It replaces the popular BladeRF; I sold mine to by the new model.



DATV Express TX software is available for the LimeSDR; https://discourse.myriadrf.org/t/windows-based-dvb-s-s2-t-transmitter-for-limesdr/1348 (https://wiki.myriadrf.org/LimeSDR-USB) . It worked well without any hitches on 23 cm, with both TX and RX running on the same computer. I am currently using my main PC, but will move it to my fast Dell laptop for project work. With all the test gear, its a real kitchen table job. I might try the table in my new room, just need to tidy it!

One of the purposes of running  DVB-S is to compare power measurement techniques with it and with DVB-T. I have discussed power measurement of wide TV signals in earlier posts.

Another purpose is to investigate cavity notch filters with DVB-S as it seems to have problems with "spread" when the power amplifier is driven too hard. I have done some work with cavity filters and DVB-T, see earlier posts.

More photos when I get it running on my laptop.


Decontis dtvtools DVB-T/S measurement, analysis and monitoring software


Decontis dtvtools DVB-T/S measurement, analysis and monitoring software (draft) 

Introduction

There has been a lack of good DVB-T monitoring software for both TX monitoring and RX measurement, unlike DVB-S that has Tutioune. I came across a commercial grade package from decontis that is relative inexpensive and uses a cheap USB-T dongle. While comprehensive, it is not particularly easy to use, but is network-based. I have managed to get it going and plan to use it for TX power amplifier modification and monitoring. My favorite element is a proper constellation chart.

Other software and hardware

The available DVB-T measurement, analysis and monitoring software is limited. CrazyScan2 for terrestrial/cable DVB-tuners https://sourceforge.net/p/crazyscan/wiki/Info/ uses PCTV USB tuner. The other alternative is to use a TV tuner, which gives MER and BER, but not constellation diagrams. A standalone TV installer instrument can be used, but good ones are expensive. Professional equipment is very expensive.

For DVB-S there is the excellent Tutioune; http://www.vivadatv.org/page.php?p=tutioune-en

Decontis

Decontis dtvtools is an excellent DVB analysis and monitoring software package. It is available for DVB-T, DVB-S and others. It is complex, commercial grade software but relatively inexpensive. http://www.decontis.com/

The DVB-T bundle, comprising SAMalyzer, SAMcorder, SAMitor, SAMbuddy-RF, SAManalog, SAMager-Agent, and SAMrack, is shareware and 50 € to buy. It is amazing value.

There is virtually nothing on the web on how to use it. A non-English YouTube is helpful. https://www.youtube.com/watch?v=T08c2yv8MeI

There are manuals for each module but none are particularly useful for setting the package up for first time use.

The sequence to use it is to install everything and connect a supported TV tuner. Start SAMcorder, use default settings and read the manual, scan your local TV stations and select one frequency. Use IP stream as output. Starting services will bring up another SAM window, select one frequency/stream, open to show channels. Clicking a channel will bring up SAMitor and the TV picture. Start SAMbuddy-RF and open both links to start analysis. Click constellation and start it to give constellation diagram. Then sit back in awe if it all works!


Use other components as desired, it helps to read the manual as it is complex software.

Issues

The software is limited by the tuner in terms of bandwidth. My interest is high quality DATV on 70cm and can use 7 MHz. I use a PCTV TripleStick 292e USB that can do 6, 7, and 8 MHz. Generally, dtvtools only supports tuners which support Microsoft DirectX BDA technology.

It is possible that the HiDes RX dongles might work as they are BDA. I quickly tried an old UT-100D with no success, but I am fairly sure it was the wrong driver. It unsuccessfully scans the device. I will investigate further later.

The software is available as a DVB-S bundle. I haven't tried it. It is hard to beat Tutioune hardware and software.

SAMcorder has an ASI input and a IP stream output which may be of interest to some.

TV Tuner

For compatible tuners see p6 of SAMbuddy-RF. Others may work. Generally, dtvtools only supports tuners which support Microsoft DirectX BDA technology.

I use a PCTV TripleStick 292e USB. It is a pretty amazing device, like most tuners, a SDR frontend.

http://www.pctvsystems.com/Products/ProductsEuropeAsia/Hybridproducts/PCTVtripleStick/tabid/308/language/en-GB/Default.aspx

http://blog.palosaari.fi/2014/04/naked-hardware-15-pctv-triplestick-292e.html

Silicon Labs Si2157 tuner