Any interest in a transverter for the LOW bands?

[VK3XDK]

Update,
Due to small changes (optimizations) I have had to re-order a few parts. This is the main delay.

Documentation is well underway, Im spending quite a bit of time on it due to the fact that many may not have used a transverter before. Many have also not soldered SMD style boards.

I am planning to offer some fully built and tested boards for those that lack confidence or time to build themselves.
I currently have a few built and tested boards that I'm offering for $200 each. (please send an email if interested grumss@yahoo.com.au ) (does not include heat-sink or simple relay system)

cheers, Graham

[VK3XDK]

Finally able to get the schematics to work on the logger!

A couple of minor changes.

I have also an alternative layout that will be implemented on the next run of pcb's that uses a 2n2222 instead of the MMIC, doesn't really make much difference but easier to source.

[VK2XAX]

Hi all,

Being the proud recipient of one of Grahams built boards I have now built it into a nice box with a Minikits sequencer to control it all.

it puts out 10 watts

Cheers

Tim

[VK4RF]

Sounds like the way to go for me as well.

[VK3XDK]

Hi again,
A couple of people have commented that the price for the fully built is a little high.


So
I have decided to lower the price to $170, could those that have already paid $200 please email me? (I try to sort out some refunds)

The kits are still a bit off, I suggest the fully built to those that are impatient. (construction documentation is the main delay)

cheers, Graham VK3XDK

[VK3XDK]

Here's a photo of mine,
you may notice that a solid diecast box is adequate for low duty TX. (the finned heatsink was used as a spacer and "just in case")

further note:

I have used the the transverter (as pictured) as a beacon. Running continuously it did get fairly hot after a couple of hours. A small external fan became necessary.

[VK3ACA]

Hi Grham

Very nice picture of unit in a diecast box, are there a stand off washesr underneath the board between the board and box?

John VK3ACA

[VK3XDK]

Yes there is john,
but they are not washers or pillars, they are just nuts of the correct height. (they dont need to suit the threads, they are just being use as spacers.)

[VK4WDM]

I got my built up board (Thanks Graham). Glad I did not attempt to build it myself with my eyesight!

Tim, very nice job! can you post a diagram of where the various leads go between the sequencer and the tranverter board please? Difficult to see from the photos.

73

Wayne VK4WDM

[VK2XAX]

I got my built up board (Thanks Graham). Glad I did not attempt to build it myself with my eyesight!

Tim, very nice job! can you post a diagram of where the various leads go between the sequencer and the tranverter board please? Difficult to see from the photos.

73

Wayne VK4WDM

Thanks Wayne,

Yes, I'll draw up a diagram of how its fits together and post that soon.

regards

Tim

[VK3XDK]

Further update,

I continue to find small enhancements in the tx section (Rx section is perfect?? ), so the kit release has been further delayed.

The board was originally designed for 1-5W, this it does very easily and will drive a high power amplifier as intended.

But in the typical "amateur" manner Ive been pushing it to its limits! I have actually seen 30W with a couple of changes but this level is not easily achieved and the harmonic levels are high (-32dbc)
The main restrictions on the power output (as is) are,
Output capacitors, ferrite output coils and drive.

A 2n2222 transistor instead of the MMIC offers a bit more drive, the drive loading can also be lightened for a bit extra. (Ive got some work to do in this section, also thinking about adding a filter/impedance match here))

A IRF510 MOSFET although rated lower than the current IRF520, has more gain and thus a higher output can be achieved (BUT I'm slightly above its rated limits at 30W RF output (3.4A? @ 13.8V))

The output ferrites need to be up-sized if greater than 10W is desired, I have found some that suit but will need a larger pcb to suit (possibly coming soon).
I have experimented with handwound coils (on type 68 and type 1 iron powder), other than a bit of heat, they offers little improvement on the "power" type coils that I have recently found and are hardly worth the extra effort.

But possibly the most surprising find is the output capacitors! At higher power they get very hot, they are obviously not the best choice. I have been consulting a few (more knowledgeable than myself in this area (thanks John VK3ACA and others))
Looks like a polypropylene or similar may be the way to go these will need to be leaded ( initial tests are looking very positive)
I am not used to the high values of capacitance needed for RF Power on these frequencies(1-30NF), In the past I would have used a "ATC" style cap but these appear to only go to about 1nf and are expensive.

So there we have it. Although up to 30W is possible I think realistically the output power (with changes) will end up being between 10 to 20W due to the need of filtering.

Is it worth the extra hassles? Most will be using an external amp anyway!

Thanks for the great feedback (those that are already having a play)

cheers again, Graham VK3XDK

[ZL1UJG]

Hi Graham,
Great news on the improvements. Yes the capacitors can be an issue.
I did an article about lossy capacitors a year or two back.
http://qsl.net/dl1gsj/The_Molded_Mud_Saga.pdf
Although the addition of RF current would definitely show issues.

Kevin

[VK2XAX]

Hi All,

Just thought I'd mention that I've performed SNR measurement on the transverter and it comes up as ~0.8uV for ~10dB SNR in 2.7Khz bandwidth

So it's sensitivity is quite good

I used an Hp8935/E6580 test set to make this measurement.

Screen dump of analyzer with relevant information highlighted included below...

regards

Tim

[VK3XDK]

Thanks Tim and Kevin,
For other readers, sensitivity (although very good) isnt our greatest concern on this band. Most of us in-fact are likely to find benefits by using the IF transceiver's attenuator.

And re. capacitors- great report Kevin, unfortunately 10nf caps aren't easy to find as NPO from what I have seen. The polypropylene may be the go? I'll update after further testing (Im waiting on some to arrive)
Luckily I left a bit of room on the PCB where a couple of leaded components should fit

BTW.
I have 5-10?W built boards still available to those interested. They are just as good as future boards apart from some possible power increases? (if they work to satisfaction). We are talking a just noticeable increase at the other end (3db at best)

I am doing my best to not let early customers suffer and will ofter email (or postage) based modifications as applicable (beyond a so called Warranty!). Please understand the difficulties I face advancing the design! (most would keep them secret until V2??)

cheers, Graham VK3XDK

[ZL1UJG]

Hi,
Although I measured the Capacitor Q factor on a LCR meter, another way I measured or checked the Q factor, was by making a Series or parallel LC circuit, and putting that between a 50 ohm generator and 50 ohm detector. The tuned circuits were in shunt and series respectively, and then looking at the depth of notch.
If one has a Spectrum analyzer and a sweeper (or a noise generator and RX) one could check components

I think I saw a graph somewhere (an ARRL book) and even a formula and one could work out the combined Q factor, If one knows the Q factor of the L, then the Q of the Capacitor can be calculated.

The Polypropylene capacitors are very, very good according to audio experimenters, and the Q factor certainly measured excellent at lower frequencies.

I have quite a selection of polystyrene capacitors here (somewhere) and if some values are needed for experimenting, drop me an email.

Kevin
ZL1UJG

[VK3XDK]

Quick comment,
The polypropylene caps arrived today,
On the boards that i tested them on, they showed very good improvements with output power, cleanliness and best of all- they don't get hot at maximum power (Power levels 10-15W)
Types tried were,
WIMA MKP-10 (400V)
and
WIMA FKP2 (100V)
Looks like they are the go for RF (in the larger capacitance ranges)

there are some cheaper ones available but I dint want to take the chance, maybe a test for the future.

I will be sending future boards with these wima caps.

[VK3XDK]

And another important finding!

I have noted a couple of smd style Tantalum capacitors "going up with a PUFF!" in the past. (very rare! 1 in 100?)
I have up to now thought it was due to human error as the voltage ratings were suitable (ie 16V caps in a 13.8V circuit)

The latest PUFF! caused me to investigate further.
It turns out that tantalums need to be de-rated in most applications by up to 50%! Makes me wonder why they bother printing 16V on them in the first place!! (NOT HAPPY)
So I am going through the process of upgrading capacitors where applicable. They will be sent out with 24V caps instead.

Most of my previous projects run on 8V so there is already suitable de-rating.

Please bear this in mind with future projects, it may save some frustrations!
for those interested, there is more details in the following document http://www.avx.com/tantalum/data/tech/v ... eraing.pdf

[VK3XDK]

Gday all,
I have just updated my website, the 600M transverter page now includes the full (so far) documentation. (PDF file)
And includes latest changes and photos.

http://www.vk3xdk.net46.net/

[VK3XDK]

Hello everyone,
Its been a while since updates!

Version1 of the 472Khz transverter is SOLD OUT! They have been very popular with many (most) going over to Europe.

I am just finalizing the documentation of Version2, they will be available in the coming days.
Version2 has a "beefier" output section (output ferrites are twice the size) and delivers over 10Watts (typically 12Watts).

I have thought about offering it in kit form but It is likely to just cause me many headaches!
The parts are small and there is many of them, many may not have the smd soldering skills.

Even the packaging of so many parts is problematic.

So - for now, they are available fully built and tested only. I think the price is VERY low considering the hours of work involved.

AUS$160 (plus postage)

[VK3XDK]

Hi Everyone, it's been a while since update (again)

The V2 transverters continue to be very popular, with many going to Europe and the US.

I have been playing again and i have found a few "mods" that may be of interest.

I can now easily get 20W out of the boards, but changes are needed and may not really be worth it (going from about 12 to 20W will barely make a difference at the other end)

1.Change the IRF520 to a IRFZ44N (they are much better in most respects, some boards have been sent out with these in place) Bias should remain about 100-180mA unless no."2" mods are made.

2.The mosfet drain-gate feedback circuit can be changed to 1uf in series with 1K (better for low frequency stability)

3.A quality 10nf capacitor (polypropylene) from drain to ground often improves efficiency and spectrum (but varies from board to board)

4. The final coil (15uh) can have a 1nf (or so) capacitor put across it, this change changes the cheby-chev filter to an eliptic response filter (up to 10db better harmonic rejection and occasionally increases output)

5.Changing to output ferrites (5.6uH and 15uH) to hand wound on type 2 toroidal Cores improves efficiency , lowers heat (and input current) and improves the output spectrum. (Very important if the board is going to be run to 20W)


The changes will mainly suit those that wish to experiment.