Pactor-III (P-III) - What is it and why do I need it:
Pactor-III is a real-world 4x* increase in throughput over Pactor-II. Weather maps that take 7-8 minutes to download with a modem only licensed to operate in the Pactor-II mode, take two minutes or less to download with P-III - saving time and battery power. The speed increase of P-III is permanently unlocked with a license key entered into the modem at the time of purchase. Note this unlock fee is approx $150-$200 and is already included in our pactor modem package price. When comparing prices with other dealers make sure that this cost is already embedded in their advertised price.
Bluetooth - Why do I need it?
We are all familiar with blue tooth these days which provides wireless connectivity between devices. The value of bluetooth in a HF radio marine environment is that less cabling equates to a lesser likelihood that your transmitted radio signal will be picked up via the cabling and interfere with the pactor modem performance (ie reduces the chance of drop outs caused by stray radio frequency energy RF)
In technical terms, the data stream of a USB signal is located in the middle of the shortwave bands. Therefore, the USB data signal cannot be separated from the shortwave signal being transmitted or received by simply filtering. Mutual interference is possible, expecially where the antenna is located close to the modem/PC set-up (ie virtually all ship borne installations). Mutual interference in this case means that the transmitted HF signal can disturb the USB data stream between PC and modem, as well, the USB data stream can also disturb your radio's reception of shortwaves. Bluetooth can help solve this problem as bluetooth and short wave radio signals do not interfere with each other. Additionally, when eliminating the USB cable connection, the danger of ground loops and parasitic currents distorting the radios signal modulation are removed, which will lead to better transmit audio quality.
Conclusion - The choice depends on your situation:
radios.net.au recommends the PTC-IIusb modem with the Pactor-III license and included bluetooth connectivity. The PTC-IIusb plugs directly into any USB connector on your computer, (NO TROUUBLESOME USB TO SERIAL ADAPTOR REQUIRED), and provides automated radio frequency switching from within the Airmail software itself.
If however you are on a tight budget and you have 2 serial ports available on your laptop (and are computer savvy) you can of course buy the cheaper PTC-IIex modem kit,
* Actual throughput may fluctuate as a result of propagation and atmospheric noise conditions.