IM improvements using DPD with a SSPA

The question that a lot of users seem to have on their mind is "What benefits, if any do I get by using ICOMS DPD in conjunction with a Solid State Power Amplifier (SSPA)"

Well, I measured a 6dB improvement. 

Measurement setup:

• SPECAN: SDR-IQ
• TAP: VK5HW (50dB)
• ATT: 20dB
• PWR: 1000W
• ANT: Dummy Load (RL 28.3dB)
• Software: SpectraVue V.3.44 Beta 0

DPD off

Two tone test:

Result:

1st Value    -31.311dBc

2nd Value    -31.455dBc

3rd Value    -52.398dBc

4th Value    -53.545dBc

IM Max     -22.2dBc

IM Avg     -21.6dBc

NOTE: 1st and 2nd value are the two tones (fundamentals) and 3rd and 4th value are IM3.

Look at IM3 and IM5, they are nearly the same in strength.

And the below using my Voice Caller calling CQ:

Result:

1st Value    -23.996dBc

2nd Value    -31.168dBc

3rd Value    -49.526dBc

4th Value    -53.689dBc

IM Max    -29.7dBc

IM Avg    -24.0dBc

DPD ON

Two tone test:

Result:

1st Value    -31.168dBc

2nd Value    -31.311dBc

3rd Value    -58.996dBc

4th Value    -59.139dBc

IM Max    -28.0dBc

IM Avg    -27.8dBc

Well, we do see about a 6dB improvement on the two tone test which is better than a Mosquito fart. But I believe the below is quite a good example on how well it improves your VOICE signal!

And below, using my Voice Caller calling CQ:

Result:

1st Value    -20.840dBc

2nd Value    -27.582dBc

3rd Value    -57.750dBc

4th Value    -60.143dBc

IM Max    -39.3dBc

IM Avg    -34.7dBc

On average we see an improvement of 7dB again better then a Mossi fart.

So I'd say any reduction in IMD, and be it only 6dB, is an improvement. As such, I would recommend enabling DPD whilst using an RF-Amplifier however, YMMV ....

ICOM IC-7610 Firmware Ver. 1.42 DPD IM measurements

A quick update on my IM measurements for the ICOM IC-7610 with the new Version (V1.42). This Version is the third installment for the '7610 and this one has the I&Q output fixed. I've not tested this but I believe that quite a few forum members have done so and are over the moon.

Here are a few IM measurements I made after the Firmware upgrade.

TRX: ICOM IC-7610

SPECAN: SDR-IQ

SOFTWARE: SpectraVue 3.44 Beta 0

TRX Power: 35W

The above shows the output without DPD. About 23dB 

NOTE: This is 6db below PEP. 

Here we see the same two tone signal with DPD enabled, a nice 54dB down on IM3 and all other IM products are below -140dB. Again, this is 6dB below PEP. So pretty darn good if you'll ask me.

And so the question remains, is it worth to enabled DPD even if we would use an amplifier? I'd say definitely. Using an Amplifier with a much cleaner exciter would give you a cleaner signal (yes yes it depends on a few other things but hope prevails ....)!

Remember GIGO (Garbage in = Garbage out)! This is also true for RF amplifiers not only for Computer Systems.

Nice going ICOM.

See the below pictures how my signal looks over the air. Solid state Amp and DPD enabled. 

• 20m
• 40m