I purchased a 1.2m Hua Hong four-band glass fiber GP antenna, covering the frequencies of 29.6MHz/50.5MHz and the UV band. The resonant frequency was accurate during indoor testing, and the SWR values were all below 1.5. However, when installed with the aluminum pipe (approximately 20m high, 0.5m from the wall) and attached to the galvanized steel pipe support on the exterior wall using a clamp, the resonant frequencies for all four bands decreased significantly, making it unusable.
After testing, it was found that contact with the exterior galvanized pipe significantly affected the resonant frequency. When the antenna was removed and kept at the same distance from the wall, UV performance returned to normal. Therefore, a plastic film was applied for insulation and fixing, which restored the UV performance to near-normal levels.
Currently, the resonant frequencies of 29.6 MHz and 50.5 MHz are still approximately 2-3 MHz lower than expected. This seems to be due to the influence of the aluminum alloy extension tube (the internal test accuracy without the aluminum alloy sleeve is not accurate). Should the aluminum alloy sleeve and the antenna body also need to be insulated? Is this a common issue with all GP antennas, or is it a specific quality problem related to the production of this particular antenna?
I'm curious to know if anyone else has encountered this issue and how they resolved it.
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