Bandpass filters for POTA

This is N2JIM, Jim, and I’m here to discuss an exciting development in our ongoing quest to optimize our Parks on the Air (POTA) activations.

Recently, Rick and I have been experimenting with a technological solution to mitigate RF interference when multiple operators are activating within close proximity: Bandpass Filters.

The issue arises when several of us activate in the same park, even when operating on different bands. This proximity results in QRM or human-generated RF interference, leading to potential disruption in communication.
To address this, we have been testing non-powered Bandpass Filters, compact devices approximately the size of your fist and featuring two SO 239 ports. These filters are placed in-line between the radio and antenna, connected with a short coax jumper. It’s important to note that these filters are not bi-directional, so proper installation with the radio and antenna connected to the correct sides is essential.
The Bandpass Filter functions by filtering out RF signals outside a particular band. This effectively minimizes QRM from nearby activators. Our tests have shown promising results, indicating that these devices are highly effective in resolving interference issues.
Currently, the Bandpass Filters we have are single-band only, requiring a filter change when switching bands. However, we’ve found them to be a cost-effective solution for POTA enthusiasts.

You can purchase Bandpass Filters from various suppliers, including DX Engineering for around $165 each. However, we were able to find them on Aliexpress for approximately $50 each. It’s worth exploring Aliexpress for various options, as prices may vary. Try using search terms like “bandpass filter 28” to yield relevant results. Be aware that these filters are sourced from China, with an estimated delivery time of about ten days.

Rick would like to share a quick tip on international orders: always use a credit card when purchasing from overseas suppliers. Credit cards offer more robust global consumer protection compared to debit cards. This is particularly important in situations like his, where he was able to obtain charge-back refunds for undelivered filters, thanks to the protection provided by using a credit card.

We’re excited to continue refining our POTA activations with these Bandpass Filters and look forward to seeing you all at the park soon.
Best regards,
N2JIM (Jim) & KF0RIK (Rick)