USING IC7610 (Ver 1.41) WITH DPD AND SPE 1.5K-FA AMPLIFIER
Several of us have experienced that trying to use the new Digital Pre-Distortion (DPD) on the Version 1.41 Firmware update for the IC7610 and simultaneously use the SPE input ALC to control the drive level, results in erratic ALC voltage fluctuations which produces erratic Pout with potentially dangerous spikes along with zero output dips.
Bob N6TV pointed out that the current choices seem to be:
1. Do not use DPD and connect the SPE ALC to control the drive power.
2. Use DPD but disconnect the SPE ALC and manually adjust the drive power.
I like the improved signal quality of DPD and I chose option 2. For a suggestion on how to disable the SPE ALC connection without modifying the existing control cable, please see HERE.
I chose to add a 3db-100w attenuator (pad) between the IC7610 and the SPE:
The advantages of this are:
1. The IC7610 operates at a higher power level and hopefully at less distortion.
2. The maximum output available to drive the SPE is 50w so it cannot be accidentally hit with 100w input.
3. If there are any spikes from the IC7610, they will be cut in half.
The disadvantages are:
1. The 3db attenuator is always in line, so it also reduces received signals by 3db. [Thanks to Dick W1KSZ for pointing this out.] In his design, AD5X added a relay, operated by the PTT line, to bypass the attenuator during receive.
2. The attenuator limits the maximum output power to drive the SPE to 50w when operating "barefoot". A relay or switch could be added to bypass the attenuator and allow full 100w barefoot operation. Or the "receive bypass" relay mentioned above could be use for this function too my manually switching it ON.
3. It waste a modest amount of power. The maximum power lost in heat in the attenuator would be 50w, but for SSB the average power would probably be 35w and for ICAS service, perhaps 20w-25w average power lost.
I have experimented with a 6db-100w attenuator, but found that the 25w maximum output does not allow getting full power out of the SPE on all bands/modes. I did not try a 5db pad which would give a maximum output of approximately 33w. Other pads are available such as ones listed HERE.
I chose to use an MFJ-264 Dummy Load and an Ameritron ASP-200 to form a 3db splitter with half of the IC-7610 power to the Dummy Load and half of the power to the SPE Expert 1.5K-FA.
It is possible to construct a 3db attenuator using 3 power resistors such as the ones shown HERE. All values are approximate. Adequate heatsinking and/or cooling and shielding must be provided, so it is not as simple to construct as the schematic might seem to show. To construct a similar (BUT NOT THE SAME SPECS) as the attenuator, Phil AD5X used thick-film resistors. A pdf of his article can be downloaded HERE.
I made a table similar to the one shown (Page 41 of Users Manual) for using a FLEX transceiver with an SPE amplifier, and refer to it to manually set the drive power:
KEEP IN MIND THAT THIS TABLE IS WITH A -3db PAD, and the actual drive to the SPE is half of these values.
WITHOUT THE -3db PAD ALL THE DRIVE POWER LEVELS SHOWN MUST ALL BE CUT IN HALF TO AVOID POTENTIAL DANGER OF DAMAGING THE AMPLIER
Hopefully in a firmware update, SPE will offer a menu option to set the drive power automatically by band and power level like they offer for the FLEX radios (see Page 41 in Users Manual), or (unlikely) Icom might offer new firmware which would restore the ALC response time to that of the Pre-DPD value so that the SPE dynamic drive control can be used again. It is a wonderful feature and I really miss it.
73
Wayne W4TZB
Ver 4: Revised 26 April 2024