Fulcomm 2303 modifications

[hpssb]

Plan is NB down = 10Kc shifter to get the A channels, PA down to give 21-40 on dial positions 1 to 20 (i.e. adds 20 channels), and both down to give 27.415 to 27.605, this will let me get on 555 upper when the overseas skip is running. They did similar to my Hy gain V and it works awesome, heaps quieter and clearer than the current Ares etc china SSB radios on Amazon are. Tech said completely do-able if I could get him a schematic, so again, thankyou!!!

 

[PY2ADN]

Thank you very much!!!! Files and radio will be on the way to the tech on Monday for its 40/60 channel conversion.

Unfortunately, the Fulcomm 2303 is synthesized using crystals, not PLL, therefore modification is not possible... ...or rather: it is possible, but you will have to assemble a (noisy) DDS oscillator, completely modifying the circuit.

 

[hpssb]

Unfortunately, the Fulcomm 2303 is synthesized using crystals, not PLL, therefore modification is not possible... ...or rather: it is possible, but you will have to assemble a (noisy) DDS oscillator, completely modifying the circuit.

I'm sure the techs knows that. They add a digital filter of sorts (way beyond my level of understanding!) to clean up the DDS thing. No noise or splatter etc audible to my ears on the Hygain, and they show it's clean with a spectrum analyzer screenshot. An Ares china SSB radio is way noisier.

Link to a page below showing how they did the hygain. Video of it on 35 at the end. It's in my user name (I set the account up for them, they didn't want to be named doing possibly illegal work which might impact their government work).

If you need any more technical details, PM be and I'll (with their OK!) pass on their contact details. Don't ask me technical details, I'm no tech or engineer!

Hygain conversion

 

[AudioShockwav]

Let me explain, I brought this out of the Sams thread because it looks like a cool mod and It should have it's own thread..
The link hpssb posted is very detailed.


73
Jeff

 

[nomadradio]

Folks accustomed to the design of 40-channel SSB radios since the 1980s will expect the radio's internal carrier frequency to shift up and down to select upper or lower sideband. This is done by making the crystal filter's passband, or "frequency window" more or less symmetrical. A lot of 23-channel SSB radios did this differently. The internal carrier frequency is the same for all modes. The crystal filter that slices off one sideband and reduces the carrier level is built to favor just the one sideband this gets you. Some folks say those sound better. Who knows?

Selecting upper or lower sideband gets accomplished downstream from the sideband modulator by changing the way the local-oscillator gets mixed with the receive and transmit signals. For one sideband, the channel crystal synthesizer frequency is below the channel frequency. The channel frequency is the sum of the two added together. Just as an example, we'll call this one the lower sideband.

To get the opposite sideband, you feed the internal carrier frequency into a frequency doubler. This gets mixed with the crystal synthesizer's output to produce a new local-oscillator frequency that is above the channel frequency. Above it by exactly the internal carrier frequency. Doesn't sound like a big deal. When we mix that internal carrier frequency with the local oscillator, it gets inverted. When the frequency of the internal carrier frequency rises, the difference frequency falls. What was a lower sideband is now reversed and becomes the upper sideband. Never mind what made this arrangement look more efficient to the designer than using two carrier frequencies. Bottom line is that to use a DDS to take the place of the original channel crystals it has to do this above-below dance when you change sidebands. A little more trouble than expanding a typical 40-channel radio.

Cool link, thanks for that.

73