Hi,

I recently built a small 4m/70MHz amplifier with an assumption that SunSDR2DX DAC OUT would produce 10dBm/10mW of power. However, measuring it using ExpertSDR3 and Tune button (slider 100%) I can only see a maximum of 1.5mW/1.7dBm respectively.

As the manual says "10mW MAX", is this normal or do I potentially have a blown out LNA somewhere on the DAC OUT path?

In all other ways the radio is operating within specifications, both HF and 2m.

Best regards,
Pasi OH2TWI

Investigating further, DAC OUT power seems to be band dependent. On 2m/144MHz I get 6.5dBm, while on 20m/14MHz it is -1.4dBm.

Hello Pasi.
1. Yes, DAC OUT output power is not linear, 10 mW is indeed max output power which can be produced on some bands.
2. What is the s/n of your SS2DX?
3. Please clarify:

Hi,

Thanks for quick reply.

1. Ok, I'll design a small LNA+BPF in between
2. My SunSDR2DX serial is EED06202100498
3. I tried DAC OUT on 20m band and got only -1.4dBm / 0.7mW output. Didn't record it though, so I might re-check. On 2m DAC OUT gives 8.1dBm/6.5mW.

Hi Roman,

I did rough DAC OUT measurements, LSB/USB Tune 100%. My attenuator & cable insertion losses likely contribute ~1dB.

Band dBm
160m +9.0
80m +7.5
60m +7.5
40m +6.4
30m +5.4
20m +2.1
17m -0.1
15m -1.1
12m -0.5
10m -1.3
6m +1.0
4m +0.6
2m +6.5

It is noteworthy that 10m band has the lowest output, while it is common for transverters.

Best regards,
Pasi OH2TWI

So to use my 4m PA with SunSDR2DX, I need to bump 0.6dBm (1.12mW) into at least 10dBm (10mW), or preferably closer to 20dBm (100mW). Typical LNAs usually have below 0dBm input and when attenuated, there is easily too much noise for the PA. Any suggestions for a simple preamp for DAC OUT?

Hello Pasi.
Your SS2DX doesn't have the DAC OUT and TX filters hardware upgrades, that is why the output power via DAC OUT is uneven through all bands. Its PA power amplification coefficients are high for some bands and lower for other bands.
After we've implemented the DAC OUT and TX filters hardware upgrades, we were able to lower amplification coefficients since TX path overall effectiveness significantly increased. Now, real output power via DAC OUT is 1...3 mW. I've already corrected the info in the UM, will publish it later with other corrections.