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Update on the Alpha mag loop antenna

randall krippner
 

 I have not, alas, had much time to play with it, but when I have, it has definitely been impressive. Mostly it's been hooked up indoors, connected to a Kenwood TS-990. Primarily it's been used for FT8. I've only been outside with it using the Yaesu 818 a couple of times.

Overall it works very well indeed. I run FT8 at about 10 - 20 watts output. Reception reports shown by PSK Reporter look impressive. Comparing it directly with my outdoor OCFD indicates it's giving me virtually the same coverage with 20 watts or less as my OCFD does with 80 watts. Of course a lot depends on the equipment being run on the other end, especially the antennas used on the receivers. But the antenna is definitely doing better than I'd ever hoped as far as transmitting goes.

On receive the results are a bit more mixed, but still not bad. I suspect some of the differences are due to it being indoors, in an area that is surrounded by computers, printers and other electronics. Outdoors on receive it's been pretty darn good.

It can definitely be annoying, though. Tuning the thing is both straightforward and tricky at the same time, if that makes any sense. Standard procedure is to tune the transceiver to the frequency I want to use, then using the antenna's tuner to bring the S meter to a maximum level. This usually tweaks it so that the SWR will be reasonably close to something close to usable. Then switch the rig's meter to SWR and dial the power down as far as it will go and hold down the key briefly in CW, or key the mike in AM or FM. Then very, very, very, very slowly turn the antenna tuner knob to get the best SWR. I can generally get the SWR down to 1.5 or better on just about any frequency on any of the HF bands. The tuner is very, very touchy. Turning it a tiny fraction of a degree can have a huge effect on the SWR. You need to have a very light touch on the tuner knob and have patience. It's very easy to shoot past the perfect spot and see the SWR suddenly jump up again.

And hand capacitance can be a serious issue with this thing. Tune it to an SWR of 1.5 or less, then take my hand away from the knob, and the SWR will jump up to over 2. Eventually with enough experience I've learned to compensate for that. That's a very common problem with antennas like this, though, so it isn't a problem with the antenna itself. Hand/body capacitance has always been an issue when working with antennas that you are close to or touching. There is a remote tuner available, which makes it a lot easier to use the antenna when it's farther away from your operating position and avoids the capacitance problem, but I didn't see any need for one because this antenna is going to be for QRP use outdoors where I'm going to be close to the antenna anyway. And if you're fairly handy it wouldn't be hard to build one using a stepper motor and a microcontroller or RaspberryPi.

But my goal for this project was to keep it as simple as possible, just an antenna, the Yaesu 818, battery pack, and a laptop to run digital. And maybe a CW key. 

So far I've been running the 818 on it's internal batteries, either the rechargeable battery pack or AA batteries. Works reasonably well with either, although you can only run 2.5 watts or less when on the internal batteries. I've had it out a couple of times, trying to make contacts on SSB. I did make one contact and, well, it was rather embarrassing, really. I threw everything into the back of the car one day when my wife was gone, drove to a local lake and set up on a picnic table. I called CQ a couple of times and to my utter amazement got the first and, so far at least, only SSB contact I've made with the 818.

It was embarrassing because it turned out he was set up at the boat landing on the same lake, about a thousand feet from me. Still, it was a contact, right?

 

LOL, good story on the contact.

I was considering one of these but it sounds like it's no faster or convenient than the CHA hybrid-micro and my ZM-2 atu.

I know OH8STN has both setups but I dont recall him doing a head to head on them.

Last saw he was sticking the milwhip on the super runner for some reason.

Thanks for the report. Would be good to see 5w js8call results on both it and an EFHW or OCFD using same placement and setup.

My QRP setup is currently the trail friendly and no tuner, but have not got linux on my android tablet yet to run fldigi in field with js8call.

I'm about done with SSB outside of the house 100W rig.  Hooked on JS8Call now!

On Mon, Aug 5, 2019, 05:07 randall krippner <randallkrippner@...> wrote:
 I have not, alas, had much time to play with it, but when I have, it has definitely been impressive. Mostly it's been hooked up indoors, connected to a Kenwood TS-990. Primarily it's been used for FT8. I've only been outside with it using the Yaesu 818 a couple of times.

Overall it works very well indeed. I run FT8 at about 10 - 20 watts output. Reception reports shown by PSK Reporter look impressive. Comparing it directly with my outdoor OCFD indicates it's giving me virtually the same coverage with 20 watts or less as my OCFD does with 80 watts. Of course a lot depends on the equipment being run on the other end, especially the antennas used on the receivers. But the antenna is definitely doing better than I'd ever hoped as far as transmitting goes.

On receive the results are a bit more mixed, but still not bad. I suspect some of the differences are due to it being indoors, in an area that is surrounded by computers, printers and other electronics. Outdoors on receive it's been pretty darn good.

It can definitely be annoying, though. Tuning the thing is both straightforward and tricky at the same time, if that makes any sense. Standard procedure is to tune the transceiver to the frequency I want to use, then using the antenna's tuner to bring the S meter to a maximum level. This usually tweaks it so that the SWR will be reasonably close to something close to usable. Then switch the rig's meter to SWR and dial the power down as far as it will go and hold down the key briefly in CW, or key the mike in AM or FM. Then very, very, very, very slowly turn the antenna tuner knob to get the best SWR. I can generally get the SWR down to 1.5 or better on just about any frequency on any of the HF bands. The tuner is very, very touchy. Turning it a tiny fraction of a degree can have a huge effect on the SWR. You need to have a very light touch on the tuner knob and have patience. It's very easy to shoot past the perfect spot and see the SWR suddenly jump up again.

And hand capacitance can be a serious issue with this thing. Tune it to an SWR of 1.5 or less, then take my hand away from the knob, and the SWR will jump up to over 2. Eventually with enough experience I've learned to compensate for that. That's a very common problem with antennas like this, though, so it isn't a problem with the antenna itself. Hand/body capacitance has always been an issue when working with antennas that you are close to or touching. There is a remote tuner available, which makes it a lot easier to use the antenna when it's farther away from your operating position and avoids the capacitance problem, but I didn't see any need for one because this antenna is going to be for QRP use outdoors where I'm going to be close to the antenna anyway. And if you're fairly handy it wouldn't be hard to build one using a stepper motor and a microcontroller or RaspberryPi.

But my goal for this project was to keep it as simple as possible, just an antenna, the Yaesu 818, battery pack, and a laptop to run digital. And maybe a CW key. 

So far I've been running the 818 on it's internal batteries, either the rechargeable battery pack or AA batteries. Works reasonably well with either, although you can only run 2.5 watts or less when on the internal batteries. I've had it out a couple of times, trying to make contacts on SSB. I did make one contact and, well, it was rather embarrassing, really. I threw everything into the back of the car one day when my wife was gone, drove to a local lake and set up on a picnic table. I called CQ a couple of times and to my utter amazement got the first and, so far at least, only SSB contact I've made with the 818.

It was embarrassing because it turned out he was set up at the boat landing on the same lake, about a thousand feet from me. Still, it was a contact, right?

randall krippner
 

The comparison of the Alpha to the OCFD sounds like a very interesting idea and certainly easy enough to do. Just hook the Alpha to one of the unused antenna connectors on the transceiver and do a direct comparison looking at results on PSK Reporter. Hopefully I'll get some time to try exactly that and if I do I'll put the results up here. 

The Alpha certainly isn't for everybody interested in playing with QRP. I love the antenna but I'm the first to admit that it isn't for everyone. It's bloody expensive, for one thing, as are most of the commercially made mag loops. And while it's portable in that it's fairly compact when torn down, it still takes up a decent sized duffel bag when torn down, what with the LMR-400 loops and the tripod and mast, etc. Certainly it's too big to take backpacking. I suspect the average QRP'er would get just as satisfactory results using the good old fashioned wire hanging in a tree. Heck for just a few bucks you can make a wire antenna cut to a specific frequency, and for not that much more add one of those micro antenna tuners. 

Anyway, the rig I've put together is exactly what I wanted, though. I didn't want a backpackable setup, but a very portable QRP rig that was able to cover all of the HF ham bands, could do SSB and digital, was reasonably efficient, etc. That's what I ended up with, the Yaesu 818, a refurbished Lenovo laptop, a SignaLink interface and the mag loop.

I'm still dithering about power. Right now I'm running the 818 on its internal rechargeable battery or standard AA batteries but I want a bit more oomph than that so I can run the 818 at it's full 6 watt output. On internal batteries it defaults to 2.5 watts output. The ultimate solution to that is to put together a solar charged battery system with enough capacity to run the whole thing.