Scribbled Antenna Blueprints: The Secret Calling Card Of The Ham Radio Operator
I was giving a talk at a hamfest this past weekend, and someone came up to me after and handed me a card. Not a business card, rather a ripped out sheet of paper from a small notepad with the drawing of an antenna. Unfortunately, I do not know the gentleman’s callsign. He swore it worked well on 40, 20, 15, and 10 meters.
One part of his drawing, labeled an “M358”, seemed to be the heart of the project, and I couldn’t figure out what it was. I had him walk with me over to the Quicksilver Radio Products booth in the vendor section of the event, and show me what he was talking about. It was simply a “t”-shaped UHF adapter; the part number M358 references the correct amphenol product. Ten dollars lighter, I had two for this new experiment.
The idea was not difficult once I thought it through. In essence, it was the rig connected to the input of the “T” connector, with a 50-ohm load splitting off on one side, and an open 45′ length of RG8X coax on the other side. This was, according to my new friend, an old school way (“It’s buried in all of the antenna books!”) of getting on the air. He had drawn a little coax extension using a uhf female barrel connector to add to the open end in order to resonate on 30M as well.
Enjoying my usual Monday evening ham radio net night the next evening, I asked the participants of one of the over-the-air roundtables if they thought this design would work. The answer was a resounding “no”, that I would be building nothing more than a 50-ohm dummy load.
Tonight after work, having a small amount of free time I have not seen in a while, I gathered up the equipment I needed to try this out.
The Icom IC-705 transceiver, an external battery (that I never used), four short coax jumpers, an LDG Z-100 Plus tuner, an MFJ-847 digital watt meter, an MFJ-264 dry dummy load (for the 50-ohm load part of the antenna), and the RigExpert A55-ZOOM antenna analyzer. And a blackberry kombucha for a warm late summer evening refreshment.
The coaxial cable that I chose to use had been previously consumed by Georgia, the One-Eyed Pirate Puppy (no, you are not looking at a terrible splicing attempt by me…nor did Georgie lose her eye after eating my cable…)
I snipped off the nibbled end to assure the cable wasn’t shorted as a result of its trauma…
And attached a couple of cable ties to make an end insulator and attachment point.
I strung the entire cable, probably around 50′ in length although I did not measure it, along the top edge of my yard’s privacy fence, leaving a generous length to be able to attach to my transceiver.
Now, before we get into this, let’s take a look at what this open length of coax looks like with the antenna analyzer. The RigExpert scans the SWR across all of the HF (and 6M) ham bands from 0.6 to 55MHz. Each vertical blue line represents a ham band, and the frequencies increase as you progress from left to right. The rightmost vertical band is 160M and the left most vertical band in 10M. The downward pointing triangle marks the 20M band. The y-axis shows the SWR.
So, an open length of coax looks like this, with a high SWR:
And now lets look at what a short (1′) RG8X coax jumper running from the antenna analyzer into the MFJ dummy load looks like. Predictably, it has a fairly low SWR.
Ok, back to this experiment. Below is the RigExpert attached to the “T” connector, with one end going to the MFJ 50-ohm dummy load, and the other to the approximately 50′ RG8X open coax on the privacy fence.
Take a closer look at what is now happening to the SWR measurements across the HF bands (sorry it is blurry).
What the heck is this? What is going on here?! And if we just pick some static frequencies and take a peak at their SWRs, we can see that this contraption should match pretty easily on 20 and 40 meters.
Time to add the tuner and transceiver. It is getting dark outside, so you will have to somewhat take my word for it. I tune up both 20 and 40 meters without any problems.
But what I do not see are any signals on the waterfall…
As far as I can tell, this antenna is indeed behaving like a dummy load and not receiving a hint of a signal.
Disappointed, I start to take it all apart. BUT! That is when I notice that as I begin to remove the open antenna-portion of coaxial cable from the “T”-connector, a flash of activity appears on the IC-705’s screen. It occurs to me that with the center conductor only connecting and not the coax shield that the antenna is now receiving like gangbusters! A demonstration of what I mean by not connecting the coax shield is shown below.
And this is what the IC-705 waterfall looked like with only the coax center conductor attached…
Interestingly, the noise floor was extremely low. Usually I can count on an S7 or more noise floor in the city, but with this set up, 40M was backcountry quiet. I could also tune up the antenna with the autotuner. I never got a chance to try to make a contact.
My last test of the evening was to see what the waterfall would look like if the center conductor of the coax radiator was plugged directly into the antenna port of the tuner without the “T” connector or dummy load. The waterfall looked exactly the same as what is shown above.
So, in conclusion, I do not know what to make of this “antenna”. It seems that the only way it works is if only the center conductor of the coaxial cable radiator is in contact with the “T”-connector. But it seems to work the same way when only plugged into just the tuner as well. As I am always fighting the clock, I ran out of time for anymore testing or analysis.
The SWR vs. frequency plot of the proposed antenna with its strange 7 or so MHz periodicity is also mysterious to me, and probably requires more knowledge about transmission lines and antennas than I currently possess (is each SWR dip occuring at λ/2?)
In short, I do not think I have encountered my dream antenna with this one. I am somewhat curious if coax makes for a quiet receive antenna. At the end of the day, I have only managed to have more questions…
KM1NDY
I checked the Bill Orr W6SAI antenna book and found nothing like the drawings given to you. LOL.
But, a few months ago, Mike NA1XX and myself hooked up my IC-7000 to the AH-4 tuner and using my truck as ground and by laying a twenty foot long insulated wire on the hood and roof of Mike’s Jeep Cherokee, worked some POTA stations on 40m and 20m ssb with very low noise floor from Great Hill. I would suggest trying it with your van and check the results. Really. It worked. “Five by Seven here south of Boston, antenna is a Jeep Cherokee” just sounded so good! WB1EVP
Haha! I wish I was there for that one Dave!
I do not know if the gentleman was putting me on or not. Jeff AC1JR did a thorough informed write-up on it here https://blahg.josefsipek.net/?p=609 .
Very interesting in any case!
Mindy
One dark Winter night, I was listening on 28.400 with the band supposed dead, when I heard a station saying “Hello test, hellooooo test” when he stopped I tossed in my “I hear you fine in Eastern Mass, WB1EVP”. Dead silence. Then “WB1EVP, this is K0&&& in South Dakota, using 25 watts into a dummy load with a ten foot piece of coax, tuning up my HR2510”. We went on for another twenty minutes QSO and then signed off. The ham said he almost jumped out of his chair as he was tuning and I came blasting in. I suggested he test his coax and dummy load as a ten foot piece of coax makes a pretty good radiator on 10m band. He said his SWR was 1.1 I heard no other stations that night on 10m. Kinda like 6m, a magic band.
That is quite cool! In making this, I got thinking about what I could use as a 50ohm load. It got me thinking about trying to see if I could get a lightbulb to radiate. I guess lightbulbs on the air is actually a thing!
Light bulbs work. They also radiate. When I was a Novice in 1976, I bought a Hallicrafters HT-40 CW transmitter with one novice band crystal. My receiver was a Hallicrafters S-40A. Both were older than I was. I had bought the transmitter at the Weymouth Ham auction that K1RV was running. I paid next to nothing and it was mint. My antenna was a 40m dipole in my parents back yard and shack in the cellar. I first hooked up a 100 watt bulb with an old surface mount socket, a short amount of coax and tuned the tube transmitter for it’s maximum light output, about 40 watts. I “spotted” the receiver to freq when the bulb was connected and receiver was on the dipole. Of course all equipment was warmed up for 30 minutes to eliminate drift. Then plugged the coax into a manual switch so I could select TR or RCV. So I listened, then put rcvr into Standby and transmitted my rather ragged CW at 5 wpm. Then switched to antenna and took rcvr off Standby. Sounds slow but it happened very fast in actual time. I worked stations up and down the East Coast and some in Canada. Then upgraded to Tech and gave up CW. It was not “me”.
But the light bulb did radiate as I tried leaving it on the transmitter and working a couple of stations on the bulb. Horrible signal reports but I just had to try it. Many have done it, so give it a try! WB1EVP
We need to try this up on the hill!