Dear SOTA Activators
Two months ago I started using the new EF-MTR (30M/20M tri-band QRP) from LNR Precision. I am happy with the antenna, but I do not know how it works. The manual (http://www.lnrprecision.com/wp-content/uploads/2012/06/EF-403020.pdf) for the antenna does not contain any information describing its operating principles. Could anyone provide me with a short technical description of how this antenna works? It has only one trap, but when used with the stub it tunes up on three bands.
• Polarity: Depends on mounting configuration
• Design Z: 50 Ohms
V.S.W.R. Bandwidth 40M: 300KHz 1.5:1
V.S.W.R. Bandwidth 30M: 350KHz 1.5:1
V.S.W.R. Bandwidth 20M: 300KHz 1.5:1
• Power Handling: 25W CW/SSB
• Weight: 4 Oz.
• Length: 65’
• Hardware: Stainless Steel
• Connector: Silver/Tefon BNC
• Radiator #22 black poly coated copper clad
• Price: $84.95
May be I will speak at the Ham Radio 2016 in FH about the new EF-MTR (30M/20M tri-band QRP) from LNR Precision.
Thank you very much for your response.
Tnx es 73 de HB9BIN, Dr. JĂĽrg Regli
Nothing mystic!
The bulky/weighty/costly tube is nothing more than a link (with SMA shorting plug), it is NOT a trap.
LNR Manual chapt. 4 says:
"This EndFedz is a little different than OUR previous designs in that it requires the user to remove an SMA connector at the end of the 30M resonator to enable just 30M, or keep the SMA installed for 40 and 20M."
This chapter does also point out that the alignment of the 30m radiator (SMA plug out) should be done before the alignment of the 20/40m radiator (SMA plug inserted).
Re: "It has only one trap but when used with the stub it tunes up on three bands."
The red colored “stub” looks nice but it acts only as a keychain for the very small SMA connector…
Again, nothing mystic, simply an EFHW antenna with 1 link (usable either on 30m or 20/40m).
BTW 1, linked dipoles and linked EFHW antennas are in use around the world - specifically also for SOTA - for a long time (lots of discussions and examples available in the web).
BTW 2, I don’t own such an EF-MTR antenna from LNR.
I have been using this antenna for several months now and it is working very well for my SOTA activations. One thing LNR failed to mention is this antenna will also work on 15 meters with the SMA connector installed. I’ve used it a number of times and have a good SWR without any tuner on 15 meters and made a number of contacts.
Gary A. - W0MNA
That may be because LNR advertises this antenna as “the perfect companion to the LNR 3-band Mountain Topper”.
Enjoy!
BTW, the rating at 25 watts may be a bit overkill for the MTR…probably useful to prevent core saturation when people misuse the antenna as some kind of “floating multiband random wire” behind an antenna tuner, hi.
I was about to purchase this antenna, but at last moment I quit the idea. The reason is the necessity to pull down the antenna to change the band to 30MHz. If so, I can easily cut a piece of wire resonant for 30MHz and use it to the matchbox I am using for 40-20.
Am I missing any advantage of the MTR 20-30-40?
I’m confused reading this thread. The MTR is a qrp xcvr that LNR sells in addition to its line of EFHW antennas. LNR does not sell a qrp antenna for 20-30-40 meters.
Barry N1EU
Barry - I think this thread is talking about this product:
Sorry for my confusion. For some reason LNR fails to list this product on their EndFed antenna product listing page: EndFedz Specs – LNR Precision Inc
Yes, I see where you must unscrew a connector to enable 30M operation. FWIW, I’m not a fan of running EFHW on the second harmonic which this antenna does on 20M - the pattern of a 1L end fed wire is NOT broadside, with two main lobes - it has four lobes with a broadside null.
I have used this antenna for over a year now for nearly 100 activations. As a linked-dipole purest I was skeptical but after using it a short time, I found that, providing the matching device end is reasonably high off the ground (>5-6 ft) it rivaled the performance of the linked dipole I had been using. I use a home-made throw-weight and thin line to get it anywhere I need to in very short order and don’t have to drop it to change bands. I never remove the 30 mtr stub as the KX3 tunes 30 mtrs fine without removing it. I did loose the stub and called LNR to purchase another and they graciously sent me two. Great antenna with contacts from ZL to OK and everything in between. Dean ~ K2JB
Barry,
While I have not used this commercial LNR antenna, I can see the appeal of it. It looks like a viable system for many portable operators.
I use a very similar homebrew end-fed design, and it works just great. Key points:
- 66 feet of #24 teflon wire
- End-fed with homebrew, high-Z tuner with complete adjustment of complex impedance
- Link at 52 feet for 30M or 17M
- EFHW on 40M
- EFFW on 20M
- 66 feet matches on 30M using tuner and link shorted! Non-resonant but very effective!
What you say about the four-lobe pattern for the End-Fed Full Wave (EFFW) is true, except that when the 66-foot wire is set up as an inverted-L - using a large fishing pole and/or trees - the pattern is a beautiful heart-shaped cardiod shape, with a single null off the far end of the wire.
Usually I set up my wire running north, sometimes south, and I have an almost omni-directional pattern on 20M except in the direction of the far end of the wire - away from the support pole. Here in Colorado, this is almost ideal.
My RBN spots and results using this setup are just fine. I use a KX2 at 10W - it’s almost overkill.
Look at my recent RBN spots up now and see.
With the 52-foot link open, the wire is close to EFHW on 30M, and EFFW on 17M - similar patterns with the inverted-L.
I prefer using a tuner so I can get perfect matches, no matter what the set-up is on the mountain - operating on solid rock, deep snow, high or low wire, far end of wire very low above tree-line, wire running through a tree, etc. Using resonant tuners has taught me how much antenna impedance may change, depending on the many variables at the site. Often I cheat and use forced matches, non-resonant combinations, usually with no counterpoise - I save time to make S2S contacts, etc. After a while you learn your tuner and its settings, and then you have real flexibility.
My tuner sits on the ground - no need to suspend it or fool with it.
Otherwise, just use an autotuner!
Opening the link is very easy using a ~6M fishing pole tied to a tree. Just lift the pole, tilt it, and the wire drops to where the link can be reached. Tilt the pole back, and get back on the air. I like to get up once in a while anyhow, so this works well. Even when I guy the pole above tree-line, it’s easy to tilt it over to change a link.
Often the link can be reached with a long stick, if the wire’s not too high - the pole bends, so you can just pull the link down without even tilting the pole.
I use dacron string and mini-banana connectors for my links. They are almost weightless and survive abuse and violent winds well. If something breaks you can make it work in the field.
Once of the big advantages of a resonant tuner like mine: it provides additional selectivity for the radio. When you have a couple of guys running 10W, set up only 100-200 feet apart, having tuners can make for a much happier activation when we’re both on different bands at the same time. Receiver selectivity is sharper, and transmitter spurs are limited.
N0TA and I often run simultaneously on different bands using these 66-foot antennas and tuners, 200 feet apart, with almost zero interference. It helps if the wires are not broadside to each other.
Anyhow, the basic concepts of the LNR antenna are sound. Their best feature is the matching network without knobs. For many operators, average sites, and some radios, this is good enough. Just note that however you cut the wires to resonate the three different bands, there will be impedance changes depending on your site and set-up. Isn’t this obvious ? Try some Eznec models to see how much Z of an EFHW can change just with height!
73
KX0R
Barry,
Very interesting, and a couple of questions for you.
Do you use a counterpoise of any sort, and have you ever tried it on 60M or 80M?
Regards,
David
G4ZAO.
David,
From context I think you directed your question to me.
I usually don’t use a counterpoise with the 66-foot end-fed wire. If the antenna is resonant and high-Z, a counterpoise usually has little effect. The test is whether the match impedance changes significantly when the counterpoise is connected. If the counterpoise carries current, the match will change when it’s connected or disconnected.
I have tried the 66-foot antenna on 60M using a long counterpoise (52 feet). This happens to be my second antenna. It tunes up OK, with a low impedance; my tuner matches it OK. I rarely operate on 60M.
I have never operated SOTA on 80M so far.
I have no idea whether the EF-MTR antenna from LNR will operate on lower frequencies than 7 MHz with a tuner - perhaps others have tried this.
73
KX0R
This got me thinking… I have the LNR 10-20-40 QRP and the MTR… but for the last couple of years I’ve pretty much used a Link Dipole exclusively… (with links and extensions to cover bands 20, 30, 40 and 60m)
When I originally tinkered with the 10-20-40 QRP version, I tuned it in sort of an Inverted v configuration… figuring that would be the easiest configuration to replicate in the woods. SWR was around 1.5:1
After your comments I took it out today and installed it with the “far-end” IOW not the matching box end… at Approx. 20 to 25ft… SWR was ~1.2:1…
I then pushed the “middle” up to the same height as an inverted “v” and the SWR was ~1.5:1
Measurement with a Rig Expert AA-54.
OK… well… just some more data points
Richard // N2GBR