There must a a thousand articles on the ‘net on why UHF series connectors are good or bad, this is another.
The example
The example for discussion is a Diamond X-50A 2m/70cm vertical antenna on about 11m of LDF4-50A feed line, N type connectors are used throughout.
At commissioning, a sweep looking into the feed line was made using an Rigexpert AA600 analyser and the results saved. The file used for this study is a sweep from 143-151MHz.
Above is the UHF series bulkhead adapter studied in the simulation. It is 50mm end to end, the simulation uses 60mm to account for the impedance discontinuity in the mating plugs. The adapter is modelled as 60mm of lossless 35Ω line with VF=0.7 (typical of UHF series adapters).
This type of adapter is quite often used for an access panel penetration at a building entry at lengths up to 200mm.
Analysis
So, knowing the impedance looking into the feed line which normally connects to an N type bulkhead adapter, let’s model the VSWR curve seen looking into the example UHF series adapter (assuming the cable terminated in a UHF series plug.
The UHF series bulkead adapter will transform impedance, altering VSWR(50), and the effect will depend greatly on the feedline length, ranging from a best case to a worst case. This SimNEC model has two parts, one for best case and one for worst case, and each adjusts the feedline length a little to explore the limits of effect.
Above is a chart of measured and simulated results.
The blue and black lines are the VSWR curves for the measured feedline impedance adjusted a little for the best and worst cases.
The red curve is a best case, it is for the case where the feed line is 410mm shorter so that the phase of the reflected wave is such that that of the adapter reduces the reflection amplitude maximally. VSWR @ 147MHz is about 1.17, quite less than the baseline 1.4.
The green curve is a best case, it is for the case where the feed line is 35.5mm longer so that the phase of the reflected wave is such that that of the adapter reinforces the reflection amplitude maximally. VSWR @ 147MHz is about 1.69, quite more than the baseline 1.4.
Conclusions
The analysis is specific to the scenario, and results cannot be simply extrapolated to other scenarios. Each use case demands its own analysis.
The adapter, even though only 7° electrical length, significantly effects observed VSWR, in this case the VSWR looking into the adapter would range from 1.17 to 1.69 with very small changes in the LDF4-50A feed line.
I would not use such an adapter at 147MHz even though the transceiver’s use of UHF jack might imply wider fitness for purpose, and that these antennas are commonly sold with UHF connectors.