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40-Meter Antenna Shoot Out!

from Paul Veal N0AH on September 24, 2017
View comments about this article!

40 Meter Antenna Shoot Out
By Paul Veal M.Ed N0AH

Earlier in the morning darkness on July 1, 2017, at around 10:30 UTC, (4:30 a.m. MDST), I decided to compare my Cushcraft 40 meter rotatable dipole up about 45 feet on my rooftop tower, against my Cushcraft MA80/40V (80/40 meter) vertical in the backyard. I used the online resource, Reverse Beacon Network, www.reversebeacon.net (RBN) to have beacons around the world report my SNR dB signal strength on line from their location from both antennas while calling CQ over a 6-minute period. I used CW as my mode and transmitted on 40 meters with 100 watts using a Kenwood TS590S. For this test, I called ďCQ CQ de N0AH N0AHĒ twice, and repeated it often, while switching between both antennas. I slowly rotated the Cushcraft 40M RTD for omni directional coverage.

At the time, the SSN:11, SFI: 72, A:4 and the K:3. No notable QRN. At 10:30 UTC, It was after sunrise on most of the east coast, complete darkness here, and the sunset gray line was cutting across SE Asia. My RBN reports came from places past sunrise on the east coast, in darkness stateside, and from KH6, VK and ZL in complete darkness.

First, some quick background on the antennas used in the shoot out:

Antenna number one: Cushcraft Monoband 40 meter rotatable dipole, a standard issued antenna for small towers wanting to 40 meters but limited on wind load. It is fed using a 1:1 W2DU balun and is positioned in between a Tennadyne T8 log periodic dipole array a few feet below it, and a six meter 3 element 6 meter YAGI above. It feeds into my roof top Ameritron RCS-8V remoter antenna coax switch with a single feedline going down to the shack. It is 90 degrees offset from the LPDA and YAGI. That is a 30 meter dipole wire you see coming off the tower.

The capacitance hats on each end of the 40M rotatable dipole (RTD) make it easy to see on the tower using some photo editing with a ďGothicĒ setting. The tower is a 19 foot Glen Martin tower. It has been in place for the past 8 years.

Antenna number two: The Cushcraft MA80/40 meter vertical has been a great performer for me. The MA80/40V has a crummy corner location in my backyard with a large buried radial field it shares with my Cushcraft MA160V 160 meter vertical, opposite from it about 60 feet on the other side of the yard. It has around 50 radials tied to its radial plate, and is feed with a W2DU 1:1 JMP balun made by the Wireman keeping ambient RF off the buried feedline. The antenna also has a copper wire matching pin with around 8 turns, 1 inch spacing, I use to give be a lower resonate point on 80 meters. It might hurt 40 meters a bit, but as you can see, my feed-point on this antenna is well grounded, fed, insulated, and built to maximize the antenna for both bands.

MA80/40V Feed-point with MA160V 160M vertical opposite

The Cushcraft MA80/40V corner lot location

Here is a summary of my results:

From 10:29-34 UTC, the time split evenly between the antennas; The MA80/40V had 23 spots with an average range of 1,515 miles, SNR reports from 4-31 dB, with the average SNR of 7.71 dB.

The Cushcraft 40m rotatable dipole had 37 spots, with an average range of 1,622 miles, SNR reports of 1-33 dB, and an average SNR 16.57 db. Basically, an over whelming victory in numbers and averages for the 40M RTD over the vertical. But there was some interesting results in the RNB data.

The 40M RTD hit 14 beacons that the vertical did not, while the vertical only hit one beacon that the 40M RTD did not. The 40M RTD hit KH6 and ZL, whereas the vertical did not, yet both antennas shared the same distance record for the night. Go figure, right?

It was VK4CT in grid square QG62jv, in complete darkness, 8,008 miles from my grid square on DM79nn. In line with the data averages, the SNR difference was 6 dB. The 40M RTD got an SNR report of 18 dB while the vertical got a report of 12dB. Why the vertical hit this most distant of locations that night and not KH6 or ZL as the 40m RTD did, is a bit of a surprise to me. But thatís antennas for you.

There were some other interesting SNR dB differences. KM3T, 1,734 miles away, reported the 40M RTD at 28 dB while the vertical did not ping off of it at all. But at the same time, the vertical beat out the 40M RTD 6 times including VE6AO +6dB, N7TR plus 3 dB, W1NT +1 dB, W7HR +3 dB, K2PO + 1 dB, and VE6WZ at + 5 dB. It slammed the 40M RTD at KS4XQ with a SNR dB report of 8.0 whereas the 40M RTD was not heard at this location 1,268 miles away!

But reality being what it is, the 40M RTD won in a landslide. We are talking an average dB of twice as much as the verticalís, and spots in KH6 and ZL the vertical did not reach. But if I had to choose one in a contest, Iíd take them both. Being diversified with antennas, to match a variety of intangible reasons as to why one antenna works better than the other, canít always be engineered or readily explained. Having a diverse set of antennas to meet a variety of fast changing conditions is always key to having success in DX. And you donít need a lot of real estate to play. I just have a typical suburban backyard. Here is the data charted out:

I want to thank the ops who put together Reverse Beacon Network. Myself and many hams around the world use it often for propagation studies and to compare antennas. It is a shining example of IP and wireless communications being used and it is certainly is a tool for the younger generation and old timers to learn by.

This was just one night shoot out, during 5 minutes, of comparing typical small lot antennas from a low power station set up. I hope those of you using RBN will share your stories about it and if you have never used it, check it out. It is a great way to monitor not only your antenna, but signals being reported around the world.

Best 73 es Gud DX! de Paul N0AH

Member Comments:
Add A Comment
 
40-Meter Antenna Shoot Out! Reply
by AB3CX on September 24, 2017 Mail this to a friend!
Nice post. This does not surprise me, a dipole on 40M should be a more efficient radiator, and will have directional gain especially if it's at a reasonable height. It should also be an easier antenna to listen to, most of the time. Rotary dipoles on 40M are a nice relatively inexpensive way to get alot out of that band. A high dipole on 80M should also beat out a single element vertical on 80M if it's high enough.
 
RE: 40-Meter Antenna Shoot Out! Reply
by KH6AQ on September 24, 2017 Mail this to a friend!
It is incorrect to average decibels. They must be converted to linear units, averaged, and converted back to decibels.
 
RE: 40-Meter Antenna Shoot Out! Reply
by KH6AQ on September 24, 2017 Mail this to a friend!
For example, taking the first eight entries and averaging, the signal difference in dB we get 9 dB. Converting to linear units, averaging and converting back to dB we get 20 dB.
 
RE: 40-Meter Antenna Shoot Out! Reply
by NN2X on September 24, 2017 Mail this to a friend!
How high was the 40 meter dipole?
 
40-Meter Antenna Shoot Out! Reply
by K6YE on September 24, 2017 Mail this to a friend!
Paul,

Very nice article. I miss you and your daughter at the club meetings.

We just moved for the final time to Santa Clarita, California (north of Los Angeles). We will be putting up an HDX-555 tower with a HyGain Discoverer 7-3 (3-element 40-meter yagi) and either a 4-element SteppIR or a HyGain TH-11DX yagi.

Keep up the good work.

Semper Fi,

Tommy - K6YE
DX IS and CW RULES
 
RE: 40-Meter Antenna Shoot Out! Reply
by K5OX on September 25, 2017 Mail this to a friend!
I see nothing incorrect in averaging decibels. In fact decibels were created so that we could deal easily with calculating power in a linear relative manner. For example if you have 10 measurements of 10 DB and 10 measurements of 5 DB. The average would be 7.5 DB. If you had 1 measurement of 10 DB and and one measurement of 5 DB the average again would be 7.5 DB. A third example if you had 3 measurements of 6 DB and 3 of measurements of 3 DB, the average would would be 4,5 DB. A fourth example is if you have 4 measurements 2 DB and 3 measurements of 1.5 DB the average would be 1.79 DB (rounded).

All these cases produce what to me seems the correct average. I think the authors measurements are correct and his article an excellent example of how easy it is to use the reverse beacon network, and why their results are expressed in decibels. They are easy to add, subtract and divide as they are a linear relative representation of signal strenght.
 
RE: 40-Meter Antenna Shoot Out! Reply
by AF6AU on September 25, 2017 Mail this to a friend!
I would have liked to have seen a full size dipole added to the test, even if an inverted Vee. Then we see how much difference the loaded version makes compared to a full size. Maybe a few Db?

How about receive noise difference from QRM sources like power lines or broadcast AM transmitters?

Even though the comparison is a loaded short dipole verses a vertical, the results are still good to see.

What I see that's cool is that the old guys of decades past, would toss up a basic dipole on 40 or 80, and it just worked. Simple, basic, cut right, not even use a SWR meter.

Some guys like a vertical, you just need to stand up 1 element, and run radials, but if you live in a poor soil conductivity area and in a valley, not so good unless you go crazy with like 60 radials and have a source of cheap wire.

I thirst for more...
 
RE: 40-Meter Antenna Shoot Out! Reply
by K6AER on September 25, 2017 Mail this to a friend!
Paul, it has been a few years. Miss seeing you and your daughter at the BARC fest.

Cheap wire for radials can obtained at a farm supply store. Electric stainless fence wire in 17 gage will cost $18 for 2500 feet. Very strong, does not stretch much and it is solderable with a good 250 watt gun.
Besides gain some antennas will exhibit much higher signal to noise ratios due to design, height, directivity and location. I would like to see in the comparison chart the signal to noise levels difference between the antennas. Many times I have had to listen on the dipole but the vertical had more gain and used the vertical on transmit with signal level difference as much as 15 dB on long distance stations. I live on the water of Lake St. Clair. As a general rule the dipole will win out over the vertical every time if the distance is East and West (dipoles best direction) and the stations are in the US.
It would have been interesting if the vertical was as high as the dipole. Then you could see not only polarization and gain results but the noise level as well.

Nice article, keep up the good work.
 
RE: 40-Meter Antenna Shoot Out! Reply
by KK5JY on September 26, 2017 Mail this to a friend!
>> I see nothing incorrect in averaging decibels. In fact decibels were created so that we could deal easily with calculating power in a linear relative manner. <<

And that is actually the problem with averaging dB. Averaging on a linear scale (addition and division) is not the same mathematical operation as averaging on the logarithmic scale.

You can compute averages in dB, but it's not as simple as adding the numbers and dividing, because doing so would result in linear equivalents that are something other than averaging.

Remember that "adding" in logarithmic space is the same as "multiplying" in linear space. In "power dB," which is a log10 scale, adding 10 in dB is like multiplying by 10 in linear space.
 
RE: 40-Meter Antenna Shoot Out! Reply
by N4RSS on September 26, 2017 Mail this to a friend!

10db represents a signal level 10x some reference

5db represents a signal level 3.2x some reference

The average level relative to the reference is 6.6x, which is 8.2 db

The average of 10db and 5db naively is 7.5db, which implies an average level relative to reference of 5.6x

Clearly, the two approaches aren't the same
 
RE: 40-Meter Antenna Shoot Out! Reply
by N2MG on September 26, 2017 Mail this to a friend!
Yes, the averaging of decibels is not as straightforward as some would like it.

Also, the "reference" being used is not the same - it's "N" or local noise. Clearly that's not the same from location to location.
 
RE: 40-Meter Antenna Shoot Out! Reply
by K5UJ on September 26, 2017 Mail this to a friend!
stainless steel wire will suck for radial wire because its conductivity for RF is 1/40th that of copper. However, you won't have to worry about it being ripped off by copper thieves.
 
40-Meter Antenna Shoot Out! Reply
by N0AH on September 26, 2017 Mail this to a friend!
Hey Tommy! Grreat to hear from you and other Om on E-Ham- glad you all are doing well-
 
40-Meter Antenna Shoot Out! Reply
by N5RMS on September 27, 2017 Mail this to a friend!
Looks as if I need to put my 40m dipole back up on the tower.
 
40-Meter Antenna Shoot Out! Reply
by N8CMQ on September 28, 2017 Mail this to a friend!
So, a directional antenna beat a non directional antenna, who woud have thought?

Now add a director and reflector to the vertical and see what happens?

Or is it better to say, for net and contest operations the vertical is easier to use, and for DX, the rotable dipole might work better?

I don' see what the point of the 'shoot out' is...

N8CMQ
 
RE: 40-Meter Antenna Shoot Out! Reply
by K5OX on September 28, 2017 Mail this to a friend!
I agree that 10 DB is a 10X power increase. However unless the laws of physics changed since I retired, 3 DB is a 2X increase in power. If we take 100 Watts and increase it 10X we get 1000 Watts and a 10 DB gain in signal strength.

Likewise if the double 100 watts 2X we get 200 Watts for 3 DB gain. If we double the 200 Watts we get 400 Watts for 6 DB gain. If we double 400 Watts we get 800 Watts for 9 DB gain. Simple subtraction tells us that increasing 800 Watts to 1000 Watts would be another 1 DB for a total of 10 DB.

Noise that you mention would likely vary from location to location. We can assume this is random and would average out as the samples increased. Therefore for Paulís excellent empirical tests, I believe the results once again to be valid.

My point being as the power increases exponentially it results in a linear unit of measurement called decibels. They can be average and so can the noise samples.
 
40-Meter Antenna Shoot Out! Reply
by W4AMP on September 28, 2017 Mail this to a friend!
Good article Paul. Thanks.
 
40-Meter Antenna Shoot Out! Reply
by K0EX on September 29, 2017 Mail this to a friend!
antenna still looks good, Paul ~!
enjoyed the article.

-Mark K0EX
 
40-Meter Antenna Shoot Out! Reply
by N0AH on September 29, 2017 Mail this to a friend!
Actually, using RBN, you would be surprised at the number of times the vertical beats out the RTD, especially in Gray Line conditions with various layers of the atmosphere can do some really crazy stuff- - Also, besides the obvious, there are exceptions in the data that really can't be explained- that was the fun of putting this together- I have experimented for years with RBN and always have a few surprises in the results- When I have messed around with a full size G5RV, the vertical and RTD slam it on 40M except during a few minutes of various sunrise cycles- So don't be fooled by the fact a directional RTD beats out the vertical, the devil is in the details-
 
40-Meter Antenna Shoot Out! Reply
by K4JRB on October 6, 2017 Mail this to a friend!
I have an old 402CD that is a real killer. I usually break right through a pile up and am often told I am the loudest station. I used a Mosley 2 el S-402 and have several wire antennas and two of which are vertical dipoles.

The 2 el Cushcraft is usually at least 6 DB stronger than any wire or vertical dipoles. I would guess the rotatable dipole (the driven element) would be very good versus other antennas too.

73 Dave K4JRB

 
RE: 40-Meter Antenna Shoot Out! Reply
by K5OX on October 6, 2017 Mail this to a friend!
Nothing wrong with dipoles, especially if you have them high and have a good location. My friend PY1AX in RIO is just a few blocks from the beach and has a trap dipole for 10,15 and 20 up around 55 ft. And a 40 meter loaded dipole below that. I not sure the make and models but they are all rotatable. For 80 he uses and inverted V at the top of the tower.

He gets out like crazy with 100 watts, especially over the Atlantic Ocean. He's a great CW and SSB op and does well in contests with that combination of antennas and of course his near salt water location helps.

I'm a bit surprised your 40 meter dipole at 45 feet does better than the vertical for the long DX. But you have to take into consideration the dipole has gain at useful angles, but at 1/2 wave high I think the main lobe is about 30 degrees. So I would expect that signals arriving at 20 degrees and below would do better on your vertical.

Actual antenna height can be difficult to measure as it depends largely on your far field gain. And if you are on a hill, the effective height of the antenna can be much higher. Also in soil with rock underneath, the effective far field height can be higher as ground reflections may be below the surface. So a vertical is only best where an effective height is unobtainable; and that varies depending on ground conductivity and topology.
 
40-Meter Antenna Shoot Out! Reply
by N0AH on October 6, 2017 Mail this to a friend!
Going out 1/2 a wave length, the 40M RTD is more like at 70 feet going North/NE, since we are on a hill, while going due east and south its much worse. Going west is somewhere in between. o yes, I totally agree with your assessment- Thx for the input- sometimes I over-analyze and over-look the obvious- This is why I don't fly airplanes or work at nuclear power plants, hihi-
 
RE: 40-Meter Antenna Shoot Out! Reply
by N5UD on October 18, 2017 Mail this to a friend!
Nice report. Lots of variables to antenna sites. However I would expect the dipole to beat the ground mounted vertical most of the time.

Once upon a time I had a FULL SIZE 40M rotatable dipole at 90 feet. It beat the pants off of my VEES and lower 50 feet loaded rotatable dipole. It easily competed with 2 el loaded yagis in the 50 feet heights. 3 el yagis could beat me out on the DX. I did not miss much on 40M that was making it near Texas. Especially if it was morning and sigs were from the west(grayline).
 
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