Here is the list of possible problems you might have experienced with EFHW antenna models:
1. Your SWR is elevated upon the first installation.
*Check the Cables, connectors, lightning/surge arrester.
*Make sure antenna is not touching objects or being very close to objects like the roof, siding, etc.
*Never have a wire going over the tree limb without proper separation with at least rope or insulator.
*Never run wire parallel to the tower or metal pole at close proximity, three feet (1 Meter) is minimum but still expect interaction.
2. Your SWR is creeping up with power applied in longer transmissions like digital (FT8, RTTY, etc), Long SSB transmission, or CW high speed chatting.
* The EFHW transformers covering 3-30 MHz are impossible to be made without Insertion loss which is averaging at 0.6 dB on our models. That loss in combination with elevated SWR like 3-4:1 on ie 3.9 MHz used with power and antenna tuner after the amplifier, when used with our 8010 model, will overheat the ferrite core and SWR will slowly “creep up”. NEVER use power and tuner with SWRs above 2:1. Reducing power to a 250-500W is OK depending on the Mode and duration of transmission used. Our models of 1kW and 2kW can easily be used at those power levels in short transmissions like calling the rare DX but not for a prolonged period of time.
3. Your SWRs suddenly are changed after months or years of installation.
* Common mistake is over the tension of wire with supports like moving trees which will stretch any copper wire and shift the first resonance of 3.55 MHz for 8010 model or 7.1 MHz for 4010 model, below bands like 3.3-3.4 MHz and 6.8-7 MHz. That will result in a shift of resonances and minimum SWR on all bands above.
* You have installed another antenna in close proximity (like Reactive Near Field distance of 0.159 wavelengths) to the antenna wire which will result in mutual coupling and de-tuning of both antennas.
*The proximity of the antenna to home and coupling of RF to miles of wires inside your home is also a major reason for RFI (Interference to appliances and your equipment like transceivers, modems, PCs, etc)
4. Your wire broke
*It is always a sign of over tension even with the use of pulley/counterweight or bungee cords, springs, or similar. The Moving trees will easily exert hundreds of lb of tension and wire with 85lb (16ga) or 200lb (14ga) of tensile strength will break or simply stretch by several feet. Abrasion of wire if it is routed thru some insulator with sharper edges is also things to avoid. As detailed in this QST article about wire size, wire strength ultimately depends largely on the installation and sag amount you are going to leave on the wire.
5. None of the above, let us know.