Any interest in a transverter for the LOW bands?

[VK3XDK]

Just noticed, the IRL510 on the schematic should be a mosfet symbol .

[VK3XDK]

Ive spent a bit of time playing with the irl510 mosfet output stage
16dbm input gives over 10Watt output, the will need some cleaning up though. 21dbm gives over 20Watt (but the MMic driver cant put out this level (18dbm max)) Note: this is on a vero-board type arrangement.

There is LOTS of heat produced by the IRL510 and needs plenty of heatsinking. I'm thinking I may try a IRF520 Mosfet instead (It should handle the power better)

[VK3XDK]

As A 10Mhz IF is not an option for most (puts 475khz to 10.475Mhz),
Ive been looking at inexpensive/easy options.
It makes sense that a 28 or 50Mhz IF is used, this puts 475khz at 28.475 or 50.475 (talk about one extreme to another!)
50Mhz (full dil14) can oscillators are plentiful and cheap.
and I have found a seller on ebay that will produce the same package oscillators at any frequency from 1-133Mhz, Ive ordered a couple for 28.000Mhz to give them a go (2 for US$13.20 including postage)

BTW some transceivers have a transverter function that allows 10.475 to be used.

[VK5TX]

What is the seller graham?

[VK3XDK]

Here is a link to the oscillators

http://www.ebay.com/itm/OSCILLATOR-DIL1 ... 19d88797d8

[VK3XDK]

Some of the more observant may notice small changes in the schematic over time!

Likely to be many changes, especially in RX and PA section.

[VK3XDK]

An Update on proceedings!

The PCB's arrived yesterday, still waiting on mixers and a couple of odd bits and pieces.

Put together the board (up to the mixer) for initial testing.

Board worked very well straight up! (I amazed myself (It was all "in theory")) minor stability issues on RX and TX. TX fixed with a larger by-pass cap on supply. RX is good except with a bad input load BUT will be fixed in the coming days.
-10dbm Input (after mixer)(anticipated drive level (after mixer))(at the moment) gives around 8W output, I think that I'll be able to get more! (waiting on power inductors)
Second and third harmonic @ 8W is around 25-30dbc (without optional output filter) and around 30-40dbc with optional output "pi filter" There is room for improvement here.


RX stage (including "tight filters" fore and aft) is showing around 25db gain. Filters are rejecting 820khz (approx broadcast band) by over 22db (second output filter not yet tested). (hope to supply some rejection plots soon)
I'm working on some slight changes for total stability.
I am anticipating around 6-10db of mixer loss and another 4-6db if the optional RX filter is added. So actual conversion gain (so far) will be around 9 to 15db (should easily overcome losses without over-loading anything)

So there we have it so-far
The updates are shown on the included schematic (attachment)
So those of you who wish to build something yourselves, the schematic shown has a very good "tested to work" RX and TX section!

Schematic is now obsolete, and has been deleted (see more recent posts for the updated version)

Cheers, Graham VK3XDK

[VK3XDK]

*** Tested to this Pint so-far SORRY ABOUT MY SPELLING!!! (should be point) (maybe i was thinking beer?)

[VK2ZRH]

Thinking beer is good, Graham

Keep up the good work. It's good to see the thought processes happening through the development.

73, Roger Harrison VK2ZRH

[VK5ZD]

Thinking beer is good

You have beer that can think?
It's alive!!! (cue music from Psycho)

[VK2ZRH]

OK, OK. The grammar could be improved. Thinking OF beer is implied.

Now. Back to low band transverters . . .

73, Roger Harrison VK2ZRH

[VK4WDM]

I definitely won't be drinking ANY beer before trying to solder in those nasty little SMD's that we can expect in the transverter!

But I will definitely have a few beers when I get it on the air

73

Wayne VK4WDM

[VK3XDK]

The BFG196 (BFG135a) RX device is biased high, this improves IP3 (Dynamic range/strong signal handling /Intermod)
The device is running fairly hot! I'm thinking about lowering the bias a bit or perhaps having an alternative bias?

Yesterday I also hooked the transverter to an antenna and my TS2000 to have a listen.
I was amazed how much quieter the band is with the transverter in place (good-selective front end).

BTW, many will find (including myself) that typical antenna tuners will not tune low enough for this band (may be different if a had a reasonable antenna )
Typical antenna tuners are "lowpass" filters, and will let everything through under their tuning point. (actually sometimes favoring their tuning point)

An appropriate antenna and tuner is also going to help both with RX and TX (selectivity(out of band rejection)on RX and output filtering on TX )

[VK4WDM]

I have just received a copy of the book "LF Today - a guide to success on 136 and 500kc" by Mike Dennison G3XDV and Jim Moritz M0BMU.

There is a lot of practical down to earth (pun intended ) info in it and well worth the cost of 13 GBP.

73

Wayne VK4WDM

[VK3XDK]

been fine tuning some values,
Things are looking great! Getting 5-8watt out with all harmonics better than -44dbc, I have had the output even cleaner (better than -50dbc) but I doubt it can be reliable with variations in components.
There could be some more changes but I think we're close enough to call it.

From my "rough" tests, I doubt if anyone has a standard hf amateur transceiver that has the selectivity/Dynamic range or sensitivity on 472-479khz that is available with the circuit I'm supplying. (Just about to raise my shield )
But of course everything else (ie antenna/tuner) needs to be correct or result could be very disappointing?

I also need to point out (some have been confused) that this transverter is linear, so ALL modes will work! (not just the non linear modes, such as CW, FM, digital ect)

An updated schematic should appear on this forum tomorrow

[VK2CCJ]

Looks good Graham,

Might just the thing for my underutilised F817ND, any time frame for the kits ?

An interested party,
Cliff V2CCJ

[VK3XDK]

OK, final schematic (I hope )

RX conversion gain is around 10-15db (little bit higher than I was aiming for), might pay to use attenuation on the chosen IF rig.

The kits will likely be available (limited numbers) in one or two weeks, (Im waiting on some components)
Price will be AUS$80, there is a high component count. (lots of work for me )

I will try to get a photo up soon.

cheers, Graham VK3XDK

[VK3DXE]

Count me in for one please

For anybody interested in these units, I had a quick look at the kit the other night at Graham's and they look really nice.

[VK3XDK]

The RX filter changes in the last schematic give,

27db of rejection @950khz without the optional filter stage (and around 10db of RX conversion gain)
45db of rejection @950khz with the optional filter stage (and around 4db of RX conversion gain)

Low side rejection is far better (characteristic of these filters) but I havnt got any figures yet.

[VK5ACY]

Count me in for a transverter, building gear 'keeps me off the streets' !

Bill VK5ACY
BOWHILL Sth. Aust.
PF95sb