QRP mobile HF operations with the USDR+ and Comet HR7 40-meter antenna
While mobile HF operation is usually a challenge, I am happy with my setup so far.
I’ve found mobile operations to be more challenging than portable ops on the HF bands for the reason that mobile HF antennas would almost always be compromise antennas. So far I’ve found success with my Comet HR7, which is a monoband antenna tuned for the 40-meter band. I’ve been using it with my Yaesu FT-857D with moderate success, making contacts even whilst mobile.
Since my daughter (DW2RXX/K2AGA) and I swap vehicles during the weekdays, I made some gradual changes to our vehicle radio setups, with my main vehicle now running a Yaesu FTM-100D and using only V/U antennas (a long HF antenna was too cumbersome). Having sold the FT-857D, I now primarily use my USDR+ for portable operations. I’ve also decided to try it out for mobile ops.
I installed the HR7 on a bracket bolted onto the crossbar of our secondary vehicle (the bracket and L-connector are unweildy, I know, but I intend to replace it with something more stable later on). I usually stow it away folded and secured to the rear crossbar when not in use. I just extend it when operating, but I only operate it while stationary.
So far, my farthest contact is with Vando 4E9VVN around 800 Km away (from Quezon City to Iligan City), whom I received 5–6 and who gave me a 5–5 report. This will probably have better receive performance in suburban and rural areas. I was parked at Myke 4I1FCI’s gas station in the city when I did my last test.
I used the USDR+ while plugged into external power with an inline LDG-Z100 tuner. I was not able to measure the output power, but I usually get 8-10 watts on SSB on internal battery power when I operate on portable. believe external power lets the radio push out slightly more power.
This did not go without challenges, though. I initially mounted it on this vehicle using a magnet-mount, which I later found to have inadequate grounding. It was designed for a hamstick-type connection (bolt-on), and I only connected it with an adaptor. I disassembled the mag-mount with the intent of adding some grounding, but I found the shield part of the coax to have been just folded and terminated nowhere (I’m surprised I was ever able to make contacts on the 40-meter antenna I previously used with it!).
Thus, I decided to mount the antenna on a bracket bolted onto the front crossbar. This made for a sturdier mounting and grounding. I also grounded the system via the LDG-Z100 connected to the car body.
I’m happy so far. But I will be doing more tests and optimizations in the coming weeks.
Cost of equipment:
- USDR+ portable clone SDR radio was received as a Christmas gift, but it reportedly cost PhP 4,000 ($70+) bought pre-owned.
- Comet HR-7 was acquired for PhP 3,000 ($53) pre-owned around 3 years ago.
- LDG Z-100 was a swap with Dennis DW1YKX for an LDG Z-817 QRP tuner that cost me PhP 5,000 ($90) around 4 years ago. The HR7 itself is already tuned for the 40 meter band, but I believe I still get some benefits from better matching. I used to have an ATU-100 antenna tuner, which in hindsight I should not have sold so I would also have something for portable operations.
- Miscellaneous gear, like RG316 cable with connectors (around PhP 400 or $7), and a cigarette lighter adaptor plugged to the USDR+’s external power port.
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