I got a LNR Precision EFT-10/20/40 Trail-Friendly multibander, and spent a while trying to tune it today. The manual recommends tuning on the 40m band, so I trimmed until I got the minimum SWR (1.2 – quite good!) right around 7.2125 MHz – the center of the US 40m phone allocation.
The manual says that once you’ve tuned for ideal SWR on 40m, 20m and 10m resonance should also fall into place. But my tuner shows that the minimum SWR is still about 800 KHz too low on 20m, and several MHz too low on 10m. I had the antenna set up as a sloper, with the top a little under 20’ in the air, and the bottom attached via bungee cord to a normal tent stake.
From the post, I’m not sure if you have an antenna analyser or are just using an SWR bridge. If you dont have one and can borrow an antenna analyser (perhaps from your local club), I would advise that rather than just trying for the lowest SWR on 40m just with an SWR bridge and expecting the other bands to be correct. Perhaps there were two dips near 40 metres and you trimmed to the wrong one. With an antenna analyser, especially a graphical one, you can see better what you are doing and by scanning all the way from 40m to 10m, you can see what changing the length of the antenna might do on all bands.
I would also check with the manufacturer whether they expect the antenna to be in a specific configuration while tuning to resonance - perhaps they don’t expect the antenna to be in a sloper configuration, for example. It’s likely that the type of ground, the height above the ground, other things in the area to the antenna will affect the antenna. Setting up the antenna one one summit will give different results to on a different summit, that’s life. If you are not simply going to use the antenna at the home QTH, this is something you have to accept. Anything under 2:1 or ideally 1.5:1 in a portable set-up is a good result.
With an antenna analyser, especially a graphical one, you can see better what you are doing and by scanning all the way from 40m to 10m, you can see what changing the length of the antenna might do on all bands.
Its real advantage is, you can clearly spot the resonance. It’s when X is at its minimum. Mostly the resonance is a bit higher than the point of lowest SWR.
Thanks, all. I don’t have a graphical antenna analyzer, just an SWR meter – but it does compute X as well. Perhaps I should be relying on that more.
The tuning instructions specify only that you should put the antenna in its operating position. They don’t specify a particular one – and the manual does say that sloper is one of the intended configurations.
I can certainly handle some variation in SWR based on different deployment conditions, but when I’m doing the initial tuning, I’d like to get it at least under 2:1 for all bands. If that’s not possible, I suspect my best bet is to jettison 40m and use it as a 20m monobander (maybe with 10m if I can get it in there). From what I can tell, the plurality of HF SOTA activations are on 20m anyway.
I wonder if that’s a typo in the manual. The older design (EF-10/20/40 MK II) had you trim the lower section for resonance on 20m (and 10m), then tune the top section for 40m. The wire winder is also a choke, so tuning one section shouldn’t affect the other too much. Luckily, my EFT-10/20/40 TF was spot on from the factory, but my EF-10/20/40 MK II took quite a bit of trimming. You can always try sending an email LNR for clarification.
Good point Doug. The tuning section of the two manuals differ markedly in this regard. I had no problem tuning my EF-10/20/40 MK II. But I always shied away from the EFT-10/20/40 TF because those wings on the winder/coil looked likely to get snagged in tree branches.
I trimmed mine using their instructions and it worked. I trimmed 40m and everything fell into place. I was skeptical at first because 20m was fine right out of the box. I used an antenna analyzer.
The band lowest SWR points for my LNR trail friendly change based on how far off the ground I can get the far end of the antenna. My typical use is as an inverted L using a 16 ft crappie pole and the far end tied to a tree branch with a cord. For me, the higher the far end, the better SWRs on 40m and 20m. If the far end is within 6 ft or so of the ground, or over very rocky soil, SWRs can be high.
I do not own this antenna but wanted to offer some info. I have found that install locations and parameters affect the antennas a lot. Also sounds like your feed point was right at ground level which has never worked well in my extensive portable experience. You might consider setting up in a few places in diff configurations. I would def get that feed point up at least 3 or 4 feet if not higher. I use various methods to get the feed point up- attaching to my bike- bungee and walking stick- fishing line to out of reach anchor- etc. Today I actually ended up w feed point at 15’ in a tree and other end down a slope and in another tree at about 8’. But it worked great and had a 1:1 match. I use about 15’ of coax for feed line. This was a new one for me. (I was on a hike and on top of a small hill w a few trees.)
In any event- biggest issue IMO is the feed point height. Let us know how you get on! I have some pics of various installs on my site- cliffordnovey dot com
Clifford - KK6QMS
PS- reading eHam reviews- you might look there too- one guy tuned it this way “I used a FG-01a Antenna Analyzer to cut/tune for 1.2 or less across entire 20m and 10m band. Then cut the 40m portion to 1.0 at around 7.150…covering the entire band 40m with highest SWR around 1.6 at ends of band. Your mileage might differ.”
Thanks, all. I’m going to see if I can borrow an antenna analyzer from someone local (any Tucson hams reading this – want to lend me one?) and wait until I have that in hand to do any more adjustments. Now I’m wishing I’d asked on here before I started! I may end up having to solder new wire back on at the end, which would be a drag.
I do have 20’ telescoping pole, and I’ll make sure to get the feed end up in a tree or something next time I use it. Will post updates once the thing’s working!
I have spotted the same issue. Instinct tells me I should trim the bottom section to match 20m and then tune the 40 with the end shortening (I just wind this up and tape it up with a insulating tape so I do not have to cut).
I wrote to LNR for advice, let’s see what comes back as a reply…
— Update: reply from LNR —
“Looks like the 20 meter side is too long, start by trimming the radiator by about 3 inches at a time, but be careful”
— end of quote —
So, I will give it a chance, I am just surprised it is to start with 3-inch trimming at first… I am not that courageous, I will do less…