26 Nov 2012

Tenbox TX progress

Good progress today with the transmit side of my Tenbox 10m AM transceiver.

The series  modulator was breadboarded a few days ago, so today I built the 3rd overtone oscillator, the buffer and the modulated PA stage. Results were as expected with around 50-60mW of clean well modulated AM available at the output. With a single linear amplifier with around 10-13dB gain (easy at 29MHz) this will take me into the 500mW-1W carrier level, which is my design aim. As I did not have a suitable 29.05MHz crystal (anyone know where these can be obtained cheaply?) I used a 28.500MHz one on a dummy load. With this frequency, any range tests will have to be done at night to avoid QRM to SSB stations.

When the linear is added , maybe even before then, I'll do a local "drive around" test with the TX on "speech beaconing" mode (using an MP3 file on the PC) and with the RX attached to a mag-mount antenna on the car. This will establish the useable local coverage.  Assuming this power level is OK, I'll then complete the full design on a tidy breadboard and publish the initial schematics on my blog and website. After that, a PCB may be in order and a neat enclosure.

This project is great fun: a simple, straightforward and easily reproducible design and a project that will be useful at the end. Much more fun than working DX with 400W and a 5 el beam in a contest with a £5k commercial HF transceiver.  Honestly, I'm having a real ball with this.

6 comments:

Anonymous said...

Where on Earth are you getting the 28.500 3rd overtone xtal from - was it a one off?

Tony

Roger G3XBM said...

Tony I think they came from GQRP club sales some years back. They are marked "Japan" and think they were for the 28.5MHz walkie-talkies available in the 1960s. I'm looking for a CHEAP source of 29.05MHz crystals. Anyone help?

Anonymous said...

AF4K - The crystal man. He does custom cuts. But they'll be about £8 a throw. Cheaper than the usual suppliers over here though.

Tony

Roger G3XBM said...

Thanks for the tip Tony. I checked his lists but did not realise he did custom orders too.

Roger G3XBM said...

AF4K may have low cost crystals but shipping costs to th UK are a JOKE at $31 to ship just 2 crystals!!

Anonymous said...

It needs an American Ham - are there any in the G qrp club that regularly visit over here - the club could purchase a job lot - know what i mean?!