Portsdown Enhancement - Transverter Switching

[G8GKQ]

In response to a number of requests, I am considering developing a Portsdown enhancement that will allow for the system to be used to drive transverters for the higher bands with automatic switching. The issue at the moment is that if you have a 10 GHz transverter with 144 MHz input and you also want to operate on 146.5 MHz, you need to manually unplug/replug the 146 MHz output from Portsdown between the 2 systems. This scenario can be extended to a number of IF frequencies/bands, and up to 8 separate outputs could be required (71, 146, 437, 1255, transvert to 3.4 GHz, transvert to 5.6 GHz, transvert to 10 GHz, transvert to 24 GHz, not to mention 2.4 GHz and 48 GHz).

The Portsdown currently uses 2 logic lines to control both the LO filter and the output switch in parallel. A third line could easily switch to a second bank of outputs. This would be based on my current built design where I use a manually-switched miniature coax relay to route the output of my filter modulator board to either of 2 separate 4-way RF switches. The issue is that the VCO filter needs to be set correctly, and if you have 2 transverters with the same IF (as I do) you still need to manually unplug and replug.

So, I am proposing that, for transverter operation, the VCO filter is controlled separately from the output switches. This uncoupling would be initiated by the third "transverter" line (which will be Pin 7 on the GPIO) going active. A PIC will then be used to control the VCO filter, changeover relay and both RF switches. This solution allows for 4 direct transmission bands and 4 transverted bands. I do not propose to extend beyond this. A programmable output attenuator, to be inserted directly on the output of the filter-modulator board, will also be able to be set for each of the 8 bands. Suitable "transverter" labelling will be made available on the touchscreen.

EDIT The level and control lines on the DATV Express should also be able to be set and stored for each of the 8 bands.
EDIT 2 PTT switching will be by an individual line for each band/transverter - see revised diagram.

I envisage a new 8 band decode board, which will be interchangeable with the current 4-band decode board. It will have a 16F883 PIC, 8 opto-isolators to drive up to 8 transmitters/transverters, and a line of DIP switches or links to set the correct VCO filter for each transverter

The solution will also work for a single 4-way RF output switch (say for 146, 437, 1255 and transvert to 10 GHz).

Comments/alternative suggestions please!

Dave

[M5TXJ]

Hi Dave,

Silly question time. Would this mean 2 versions of Portsdown software for those who do/don't want the transverter option, a console option to turn off transverter touchscreen options or just everyone having the options in menu whether you'll be using them or not? Just playing devils advocate here as I can see with the attenuator option the menu structure getting rather crowded. I must point out I'm not criticizing as I'm in awe of what you guys have accomplished and what is still happening, I'm only thinking of newcomers to DATV like myself who might start thinking "this is getting too complex for me..."

73 Dave

[G8GKQ]

Dave

That's a great question (as Tim Peake would say)

There will be a single software build, and the rewrite that I have just started will hopefully make it simpler.

You will have noticed that the picture source buttons are all over the place and are tied up with the transmission mode at the moment. This will be simplified, and there will be a button to select subsidiary menus for all the selections, such as H264/MPEG-2, picture source, frequency, SR and FEC. One of these new buttons will select the transverter mode in/out, another will do the same for the attenuator.

The default build will ship without these new (attenuator/transverter) options enabled. So, there will be change, but hopefully you'll find it easier when you get used to the new menus.

Dave

PS We are where we are because the project started with a single Menu of 17 buttons, and it has grown to 5 menus, each with potentially 30+ buttons.

[M5TXJ]

Thanks for the explanation Dave, making menus intuitive is very hard to do so I wish you luck. I'm really looking forward to getting on the air with my Portsdown, for 2m I've only got the PA to build to be active from home, not that I think I'll be able to contact anyone from here until G4EXD and G7ITT finish their builds. Planning on going out /P when the weather improves a little.

73 Dave

[G4uvz]

My concern Dave would be the additional attenuation of the second switch plus the 2dB attenuation of the switched attenuator. Personally, as discussed, I would like to be able to use the 70MHz output for transverting..... otherwise its a relay outside of the box requiring control wires which is not so tidy.

P1090091.JPG (139 KiB) Viewed 4481 times

[G8GKQ]

Hi All

I have developed my proposal and amended the block diagram above to include 8 switching lines. The new 8-Band decode board will have very similar functionality to the current 4-Band decode board and be an easy replacement.

The proposed changes to the Portsdown software will also allow the use of some of the RF outputs on an existing single 4-band switch (Adrian) as transverter inputs. This will require the new 8-band decode board to be fitted, but the RF wiring can remain unchanged.

The drop in level through the RF switching and attenuator is unavoidable, but a very cheap MMIC amplifier could be used after the attenuator and before the RF switches to compensate.

Now that I have an outline hardware design, I will amend the Portsdown software to support it. This will be a 2-stage process: first I am going to revise the Menu system but retain existing functionality; secondly, I will add the transverter functionality.

Dave

[G4uvz]

Dave given that I have no aspirations / antennas etc to work on 70MHz ...If I removed the 70MHz LPF components and bridged RF1 and RF3, or duplicated the 2M LPF ..Would it be just a matter of redefining the 70MHz screen tab and of course the frequency output, to achieve a 2Mtransverter O/P out of the 4M port?

73 Adrian

[MN-tech]

Hi Adrian.

Here is a work-around solution for putting a transverter on the 4M output while waiting for a software solution to work its way up Dave's list.
Add a SPDT switch to move the to the output switch's LSB bit from the Pi output to ground.
This will change the 2M bit combination from the Pi to 4M.
Be warned it will also change 23cm to 70cm. Adding some additional logic could prevent this if you feel accident prone.
Setup the Portsdown to transmit the desired 2 M frequency, use the new switch to select 2M or transverter operation.

John

[G8GKQ]

Hi Adrian

The Portsdown's current definition of "Band" is based on the selected output frequency (not on which button is selected). So any selection of an output frequency in the 100 - 250 MHz frequency range will result in the 146 MHz LO filter being put in circuit, and the 146 MHz output being selected on the RF switch board; so your suggestion would only half work. John's idea of putting a hardware switch in circuit before the RF switch is a good one and is probably your best bet in the short term.

Dave

[G4uvz]

Thanks John..that sounds like a good idea! Can't beat a hardware fix when the software solution requires weeks of work!

Adrian