I have been using a Par EndFedz Mk2 Trail Friendly 40/20/10 though using the matchbox from an EndFedz EF-QUAD (with Vibroplex’s blessing) so I could transmit at more than 25W. On all three bands I have very nice SWR - for 20m and 10m around 1.1. For 40m 1.1-1.5.
Today I switched over to using the radiator that actually came with the EF-QUAD matchbox - heavier gauge wire and full-size at 40m rather than being electrically-lengthened like the Mk2. And I seem to be getting better receive performance with it.
However, I can’t get SWR much below 1.5 on any of the bands, despite the charts that come with the antenna saying it should bottom out at 1.1. By trimming (well for now, folding back on itself) I can move the minimum SWR frequency but I have not been able to make SWR go lower.
Everything in the shack is the same. And the house end of the antenna is in the same place. Now, since this radiator is 25’ longer than the other one the far end is in a different place, making this radiator actually further off the ground than the other one. However it also goes closer to trees. It is not touching any branches or limbs but does come within a couple of inches of some decent-sized limbs in a few places.
Because of my living situation I'm pretty constrained as to where I can have the feedpoint of the antenna -- I was allowed to screw a hook into the exterior windowframe. The matchbox is is attached (with a short bit of rope) to that hook. A 1-foot length of coax connects to the matchbox and to a common-mode choke just inside the window. Then a 12-foot length of coax goes from the common-mode choke to the radio. This is all the same with both radiators. There is no ground or counterpoise because I'm not allowed to run a wire down from the window. And with both radiators I measured the SWR with an antenna analyzer by connecting it to the cable that connects to the radio -- because I wanted to measure the SWR the radio sees.
After getting nowhere with reducing SWR I decided to measure the SWR before the choke. When I did that, the minimum SWR dropped to 1.1-1.2 on most bands, and dropped noticeably on all four bands. With the previous radiator I had measured SWR both at the radio and before the choke and with that radiator they were virtually the same. So I assumed (danger will robinson) that would be true with this radiator. Obviously, apparently not.
Do I just live with it (my IC-7300 internal tuner can deal with it, though it does mean some power loss -- though with only 13 total feet of coax probably not too much)? Do I drop the choke? I've done some reading in a bunch of places and things seem to be all over the place. From what I've read it appears a common-mode choke is wise when you have a random wire end-fed. But for an end-fed dipole (like this) there seems to be much more conflict about whether a CMC is needed or not.
Update with measurements:
Here are some measurements I've made to try to figure out what's going on:
- Remove antenna from choke, attach dummy load to choke, connect antenna analyzer at radio end of the cable between choke and radio: dead flat at 1.0 on all bands.
- Attach antenna analyzer at choke end of the cable to that goes from antenna to choke (i.e. measuring close to feedpoint with no choke): SWR bottoms out at 1.2 in 40m band, is under 1.5 for the entire 40m band.
- Connect the antenna/choke cable directly to the choke/radio cable (i.e. no choke) and attach analyzer at radio end of choke/radio cable: SWR still bottoms out at 1.2 and is still under 1.5 in the 40m band, but the frequency of minimum SWR drops a little.
- Connect the antenna/choke and choke/radio cables to the choke, attach analyzer at radio end of choke/radio cable: SWR now bottoms out at 1.6 and gets over 2.0 at the ends of the 40m band. Minimum SWR occurs at the same place as in (3).
So the cable from radio to choke doesn't affect minimum SWR on its own (though it does change the frequency where the minimum SWR happens). And the choke doesn't affect minimum SWR on its own, but choke AND cable affect minimum SWR. But they didn't affect it for the other radiator.
So even if it isn't that big a deal to operate with the higher SWR I'm curious as to why this is all happening.