Mod to Elecraft K2 To Use On AM - Suggestions?

[W1UJR]

Wondering what might be able to be done to get this rig on AM?
The Retro 75 is on the way, but would be neat to also mod the K2,
either with new board or existing board.

SSB board schematic is attached...suggestions?

[Steve - K4HX]

Unbalance the balanced modulator (shunt the appropriate resistance across one leg of R1 and bypass the crystal filter (some diode steering and an RC network for compensate/equal) for the filter loss). You'll probably want to disable the ALC too.

[W1UJR]

Unbalance the balanced modulator (shunt the appropriate resistance across one leg of R1 and bypass the crystal filter (some diode steering and an RC network for compensate/equal) for the filter loss). You'll probably want to disable the ALC too.

Thanks Steve, but my technical experience is not up to selecting the right value of components.
When you get a moment, could you be more specific, or even modify the schematic, to reflect this?

[K1JJ]

Bruce,

Another alternative, if you desire not to modify the rig internally; (except for in/out or relay control leads) You could build up a single chip external NE-602 balanced modulator. This was done with many FT-102's a few years back. Both Steve and I have a few rigs modified for AM this way.

You would A/B switch this circuit in place of the existing bal mod using tiny remote relays.  The circuit is found on AMfone.

Though, modifying the rig as Steve suggested above may be the easier way to go.  At least you have another option if you get stuck.

T

[ke7trp]

The idea makes me ill

[Pete, WA2CWA]

If I remember correctly, the K2 doesn't even have an AM detector so you would probably have to diddle with the receiver section too.

If you're hot for an Elecraft to operate AM, sell the K2 (unmodified - value plus)  and get a K3.

[Steve - K4HX]

You can determine the correct values by experimenting. Turn the R1 pot until you get the amount of carrier you want. Then measure the resistance on the wiper are. Select that resistance.

You'll need to measure the loss in the crystal filter. A sig gen and scope is all you need. Then place a simple resistive divider between C5 and C11. Or you could just measure the typical signal level at C11 with the filter in place. Then use a pot as your bypass network and adjust the pot to obtain the same level at when the filter is in line.

Or as Tom said, just build your own NE602 board and place it on the correct pins of P2 and P3. You'll need to supply your own audio for this board, unless you do some routing to get the K2 audio to your NE602 board. I'd go with external audio to the 602 board and be done with it. This saves you from having to modify the low level audio stages in the K2.

Unbalance the balanced modulator (shunt the appropriate resistance across one leg of R1 and bypass the crystal filter (some diode steering and an RC network for compensate/equal) for the filter loss). You'll probably want to disable the ALC too.

Thanks Steve, but my technical experience is not up to selecting the right value of components.
When you get a moment, could you be more specific, or even modify the schematic, to reflect this?

[W1UJR]

If I remember correctly, the K2 doesn't even have an AM detector so you would probably have to diddle with the receiver section too.

If you're hot for an Elecraft to operate AM, sell the K2 (unmodified - value plus)  and get a K3.

I did not even consider that Pete, nothing on RX.

The K3 is on the way, perhaps I should just shelve the idea for the meantime and concentrate on the K3.

[N8UH]

This is still an interesting idea - if the mods were easily reversible. Perhaps if the mod could live mostly on the SSB daughtercard this could be done?

I know that I can count on one hand the number of times I have used the ssb capability on my K2. It's just such an amazingly good CW rig that it would seem like a shame to use it for anything else! I was thinking of selling the ssb board.

But if it could be used as a PW AM rig... 

[W1UJR]

Hi Tim,

I'm going to do some further research on the Elecraft reflector about this, did not find anything on a quick search conducted eariler.
When I get a moment, I will send out an email to some of the Elecraft tech folks as well, would be an interesting project for those of us who prefer double sidebands. But as you say, it is an awesome CW rig, like the K1 as well, on its own!

I've heard the K3 on AM, sounds good. I recently ordered the 10 watt version, figured I'd get that one going and add options as the need comes up.

[n1eu]

The K3 is on the way, perhaps I should just shelve the idea for the meantime and concentrate on the K3.

My understanding is that the K3 AM tx will only use the 6Khz filter.  I'm wondering what would happen if the 13Khz filter was installed and configured in the menu as a 6Khz filter to trick the rig into using it.  If anyone out there has a K3 with the 13Khz filter, perhaps they could try this and report back.  As it is, it's unfortunate that Elecraft supports 4Khz tx audio in SSB (ESSB mode) and only 3Khz tx audio in AM.

On receive, the K3 WILL reportedly use the 13Khz filter (configured as 13Khz) to provide up to a 5Khz AM rx audio passband (brick-walled at 5Khz in dsp firmware).

73, Barry N1EU