06 November 2019

AS-IS CDM324 is unsuitable for 24 GHz QSO

I tried receiving the 24 GHz signal at 4 metres distance pure line-of-sight inside a room. The receiving end IF port was sent to an RTL-SDR receiver, while the transmitting end was modulated with a WBFM injected into the IF port or CDM-324 (a.k.a IPM-165).

The signal was quite weak, about +10 dB above noise and quite spread. Considering that I received an HB-100 with an HB-100 at 300 metres without the aid of extra antennas, I can state that the CDM-324 AS-IS is not suitable for WBFM (ham radio) operation on 24 GHz. This is actually the information I was looking for and did not show up in my searches.

Maybe there is a loose LPF under the hood, as shown in a video on youtube. It could explain with the signal with 50 MHz difference is weaker than the one at 25 MHz delta.

I will open one of my CDM324 and try to make it as similar to an HB-100 as possible.