***DISCLAIMER: Once again, this is not THE WAY to do NVIS, it is simply a record of my experience with my methods so far, hopefully you can learn something from my errors.***
I set out this summer to start practicing more in the field with my HF communications gear. I have gotten to the point where I can set up my equipment pretty good from my home, which has saved me some frustration and wasting of time in the field, but now I am to the point where it is time to start going into the field more and refining my methods.
The first thing I did was to build a better antenna than anything I was using previously, and that is a linked dipole setup for 20M, 30M, and 40M. After purchasing an antenna analyzer a few months back I was able to build a nice resonant (at home at least) antenna to take into the field.
The reason I went with a linked dipole is the fact that I can set it up as an inverted Vee, and changing bands is very simple. It is just a matter of lowering the feed point until I can reach the links required, and then raise it back up. I don’t have to unwind any more wire, extend guys, or anything. I can do a band change in under a minute, and that’s if I mess up. I used #18 insulated wire so leaves and vegetation hopefully don’t mess with my signal too much. I am feeding it with 50′ of RG8X.
I’m not as worried about operating from my house as much as I am operating portable (on foot), so I had to cut some station weight to do this. This meant my antenna tuner was out, which is another great reason to have a resonant antenna. So far I have set up my antenna in a variety of locations, and different heights, and have yet to have any problems with SWR.
I have to admit, that I am very much an amateur at all things involving radio communications, and this is no different for NVIS communications. There is an excellent series of articles put up by Brushbeater to help out. I can assure you I will be reading these over and over for the next few weeks.
That’s not to say I haven’t had any luck conducting NVIS. My most recent trip out was my best however. I stopped at a location with lots of pine trees and sandstone rock outcroppings. I picked up my station which consisted of my SGC SG-2020, a 7.5AH SLAB, 50′ of RG8X, some earbuds, and my linked dipole. I hiked back a little ways and found a location on top of a long rocky outcrop and began looking for a tree to hang my dipole in.
My initial plan was to look for a height of 6 to 12 feet and set up my antenna as a dipole or inverted vee because I wanted to try to make an NVIS contact within 400 miles. I looked at a few trees but they all seemed to be more trouble than they were worth. I only had about an hour to set up, make contact, and tear down, so I had to be quick, but spending the time looking for an easier tree to get an antenna into was worth it.
I finally picked a young pine tree about 8 feet tall. It was kind of scraggly for a Christmas tree, but it would work for my antenna support. After a good jump I was able to get my feed point hung in the tree.
I then went out to the ends of my antenna and looked for any branches to hang them on and a place to guy the ends with. I have about 10 feet of 550 cord tied to the insulators of my antenna with a loop in the end so I can just grab a tent stake and stake the antenna ends down. For this trip though, I chose to run the legs of the antenna over any low branches or bushes I could find, and then stake the ends down.
So once I got my feedline ran back to an operating location somewhat perpendicular to my antenna, I set my radio for a frequency fairly low in the 40M SSB portion. I did this because I had read that the lower in frequency you go, the better your NVIS comms should work. In fact, after reading Brushbeater’s articles on the subject, the 40M band isn’t really ideal, but rather 80 or 160. But, hind sight is 20/20.
I set my radio for 7.225 LSB and began calling CQ with 15 watts of power. No luck. So then I tried searching around the bands to see who I could hear and see if I could get in touch with them. I did hear some folks rag chewing, but nobody calling for CQ and no nets to try to get into. I’ve found that if I can typically hear a station, I can usually talk to them. So, with no luck there and time running out, I went back to 7.225 and started calling CQ. I was nearly ready to shut down when I was responded to by a station only 240 miles away. He wasn’t real strong, only about a 4/5, and that was about as strong as I was to him. I’ve found that a set of head phones is very helpful to have for hearing the weaker stations. While my radio has a decent speaker, it’s alot easier to hear the faint ones when the audio is being piped right into your head.
So an overall success! Our conversation didn’t last very long, but I was able to make an NVIS contact. Now I will be digesting and implementing the advice in the article’s posted by Brushbeater to further improve this very useful skill set.
Here is a project in development to keep an eye on from Survivaltech Nord. It’s a scalable, portable power back. It’s main use is to power comms gear (up to 20w), but he’s also designing it to be a portable back up power bank as well. Be sure to check out his youtube channel as well, lots of great info.
I would like to share my experience thus far with the MFJ-9232 QRP Loop Tuner. I would call this a review, but I’m not going to try and convince you whether you should buy this or not, I’ll just share my experience and you decide for yourself. This is a product that MFJ recently came out with. I’ve been intrigued by loop antennas for quite a while because of their capabilities as a low profile antenna. I’ve been very interested in a 40M loop antenna for a low profile base station antenna at home. Sadly, most of the commercially available ones were out of my price range, and were not very efficient on the 40M band. There’s also the route of building one yourself, which I would like to do eventually. For those not familiar with loop antennas, there’s a good post over at AMRRON, and numerous sources online.
When I received my MFJ-9232 it came packaged in a waterproof vinyl bag with 55 feet of #18 wire and about 10 #10 ring lugs. The first thing I did when I received my tuner was read the instruction manual that came with it, which matches the one available from their website. In this manual they recommend using nothing smaller than a 10 gauge copper wire for your loop conductor and they include a chart of lengths to get good results on each band. I started out with pieces of #10 stranded cut to the lengths in the book, and I had a little luck on 30M through the reverse beacon network, but no real luck on 40M or 20M that day. To be fair, band conditions were really poor that day, but it was still fun.
After this I went and bought 15 feet of 3/8 copper tubing at the hardware store. I double checked the length when I got it home, and hammered the ends flat and drilled a hole through them to attach to the tuner. This was the length to get onto the 30 meter band according to the manual. I had good results with this on the reverse beacon network with decent band conditions, and running 5-15 watts of power from my back deck it produced a distinct T shaped radiation pattern (according to the results from RBN).
Although I had good results on 30 meters, it took a lot of work to get those results. I’ll explain what I mean. With a loop antenna you do not use an antenna tuner, instead you adjust the antenna’s capacitance through adjustable capacitors. At the time I did not have an antenna analyzer, so I was using the method described in the manual of peaking the signal. It is a very hard thing to do because a loop antenna has a very narrow bandwidth, so the sweet spot (low SWR) is very small. The way I would check to see if I was ok was using the reverse power meter on my SGC SG 2020 in CW with about 5W of power.
To complicate things further, your hand will introduce more capacitance to the antenna, so the adjustment changes as soon as you pull your hand away. So after much frustration on 30 meters I purchased a used MFJ-207 antenna analyzer. I picked it up for about $75 and it has made a world of difference in setting up all of my antennas. Once I got the MFJ-207, I trimmed my copper Loop to 12 feet so I could try and make some SSB contacts on 20M. (This was the length per the manual)
I could clearly see the effects my hand was having on the antenna when I was trying to tune it and it was a very painstaking process to get a low SWR. I found that if I actually tuned the antenna to a 3:1 SWR, once I removed my hand it would typically drop below 2:1. I decided at this point I would extend the shaft for the tuning knob and put a bigger knob on to help make finer adjustments. To be fair, once I had it set for a low SWR, it received very well on 20M. I could barely move 1 MHz without picking up another conversation. This was obviously when the band was good. I didn’t have time that evening to try and make any contacts.
It was at this point in my experimentation that I noticed the tuning knob suddenly got a lot stiffer to turn. I took the tuner apart for the first time and realized that something was bound up inside the little variable film capacitor inside. I called MFJ the next day and they had another one coming in the mail right away. Once I received this I simply swapped it out with the original. After that I extended the shaft for the tuning knob with a 1/4″ hose barbed coupling, drilled out on one end to accept the shaft on the capacitor. Once the shaft would fit I epoxied it into the coupling, and put an 8-24 bolt in the other end. I reused a lid from a jar of peanuts I finished awhile ago for the knob.
So far the antenna is a lot easier to tune then it was before. I can usually tune to get about a 1.2 SWR, but I have very high reflective power now. I’m a little perplexed by this, but I’m thinking 12′ is not a good length after all. I’m thinking of sending it back to MFJ and have them take a look at it in case I hooked something up wrong with the capacitor. I still think that the loop antenna concept holds a lot of promise, and I would like to build one for 40 meters. As far as whether or not I would recommend the MFJ-9232….I don’t think I would for portable QRP work. It’s very hard to get tuned and I think in order to build a big enough loop antenna to be efficient on 40 meters with QRP power, it would kind of defeat the purpose of being portable. I still think the loop is more of a low profile base antenna. Therefore, you could buy one of the bigger loop antenna tuners, such as the MFJ-936B, with all the nicer features built in that make it easier to use a loop antenna.