19 Jun 2009

The SixBox - A Simple 6m AM transceiver

NB There is an updated schematic uploaded June 28th 2009.

Well, I've completed a breadboarded version of the SixBox, an ultra-simple 6m QRP AM transceiver which I've had in my mind for some time. As it stands, without a linear, it produces around 50mW AM (200mW peak) from the 2N3904 series modulated PA. It is not in a box, just a rats nest on a piece of copper clad board, but it works. The receiver is a super-regen using MPF102s with an isolating RF amplifier loosely coupled to the super-regen detector. A varicap diode (to be added) is used to tune across the band. The TX consists of a 25MHz xtal, a x2 multiplier and PA both of which are series modulated. Ubiquitous 2N3904 transistors are used throughout apart from the super-regen stages.

Click on the schematic to see what it consists of. It would readily scale for 4m although the T37-6 toroids would be a bit marginal this high. I was surprised how well they worked at 50MHz.

I should be DELIGHTED if someone wanted to develop this circuit further and maybe produce a small PCB and case.

On reflection, I think the DSB version of this would be a better bet. Much of the TX line-up can be re-used for this but I would use a DC receiver. 200mW pep of DSB (equivalent to 100mW SSB) would be quite a useful power. My next project will be to complete the DSB version, either for 6m or 10m.

12 comments:

Anonymous said...

Thanks for your efforts Roger. I will make a version over the coming months (In the middle of a QTH move at present). Would it be possible for you to develop some notes on the windings required for 4M operation? I presume the TX is simply changed to 1/2 the working tx frequency for 70.26MHz. Not an expert in this area.

Thanks.

73, Dave GW8JGO

goody said...

Hello Roger,

This is an interesting circuit; I'm going to build a receiver. Is C6 the gimmick cap or C10?

Is there enough regeneration to receive CW signals?

72
Goody
K3NG

Roger G3XBM said...

Goody,

When renumbering the parts it screwed up.It is the cap between the 2 RX coils . Just get a few mm of 32swg or similar thin enamelled wire and twist together - makes a simple small cap. Too much coupling will kill the super-regen stage oscillation.

goody said...

Good deal. Have you tried using it to receive CW? A local friend here just discovered 6m and he's looking for a new ham project to get local guys on 6m with a minimal investment.

Also, I'm wondering if one could pull a 25.000 MHz crystal far enough to get to 50.135 MHz (or more) with the doubler?

Roger G3XBM said...

A super-regen RX is no good for SSB and CW. You'd need to turn back the regeneration so it behaves as a normal regen RX with the detector stage just into oscillation. For SSB and CW a direct conversion RX is a better approach. This is what I am doing next as part of my DSB project.

A 25MHz xtal should pull around 1kHz/MHz so at 50MHz a 50kHz VXO range should be achievable. With two parallel xtals the range would be greater.

JL1KRA Junichi said...

Dear Roger G3XBM,

May I introduce your SixBox transceiver note in 2009 Japanese Arateur Radio Festivals ? Now I am preparing attractive article for 6m AM enthusiasts. I will translate it into Japanese.

JL1KRA Junichi Nakajima

Roger G3XBM said...

Junichi San,

Thank you for your interest in the SixBox. I am very happy for you to translate this into Japanese and to share the idea with hams in Japan.

73s
Roger

JL1KRA Junichi said...

Dear Roger-san, G3XBM

Thank you your prompt reply and
permission of Japanese translation.
The Japanese Ham Festival will be held in the end of August. I am sure many Japaese
builders will be interested in the SixBox. Since all parts you used in the transceiver are easy to obtain.

I will let you know the result and
of course I will send you the translated version later.

Sincerely

Junichi Nakajima JL1KRA

Anonymous said...

Hello Roger,

Having just read (In Sprat 140) your excellent articles on WSPR and The SixBox I would encourage you to continue with the 10/6 metre DSB version (with a pcb layout). That would make a marvellous base for WSPR experimentation! (Published in a future Sprat?) - and allow 'simple' repeatable PCB construction for us less gifted types!

73, Richard G8ITB

Roger G3XBM said...

Hi Richard,

Yes I intend to get on with the DSB version very soon now. I've been distracted, in a nice way, by 500kHz WSPR recently , but I do want to get a neat little 10m DSB transceiver done within the coming months.

73s
Roger

raymond tongol said...

hey mr roger will this amtransceiver will work in the philippines, we have a school project of amtransceiver i hope this will work

raymond tongol said...

will it work in philippines?