Horizontal or Vertical?

Equipment Antennas
21

In reply to G3CWI:

I personally try to test simple antenna designs in 4nec2 to get basic idea what their radiation pattern should be, how much gain I can expect and to compare antenna raddiation pattern to known antennas. I can suggest this software as it is very easy to use and you can learn it from a 15 minute video on youtube.

BUT antenna model only says what is the BEST antenna can do. This is special problem with verticals. Dipoles are good in this.

What should be considered with verticals (or any short antenna) is radiaton resistance vs. ground resistance. This two terms make the radiation loss.

radiation efficiency %] = radiation resistance [ohm] / (radiation resistance + ground resistance) [ohm]

Radiation resistance is roughly equivalent to impedance of the antenna at the feedpoint. Ground resistance is the RF resistance of ground (radial) system. Ground resistance is nearly not measurable, at least with equipment most of us have at home and should not be confused with DC ground resistance.

To show you an example, say ideal 1/4 vertical has impedance about 38 ohms. Now imagine a poorly designed radial system with one or two radials in poor soil and let’s just assume it has radiation resistance about 500 ohm.

38/(500 + 38) = 0.07 = 7% radiation efficiency

This is rather extreme example but in this case, if you used 100W, 7W will be radiated and 93W will heat the ground around antenna. Poor moles!

Now lets try the same with half wave vertical over the same ground. Common end fed half wave has impedance about 3000 ohms.

3000/(500 + 3000) = 0.85 = 85% radiation efficiency

Voila!

Conclusion from this is that low dipole can easily outperform a vertical if impropper radial system is used. This applies especially to very short verticals where radiation resistance can drop below 10 ohm easily.

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22

In reply to OK1BIL:

The interesting thing about a quarter wave vertical with few radials is that if you set it up on a rocky summit you might find a completely different situation to setting it up in your garden. In this country the rocky summits are profoundly shattered from periglacial freeze/thaw cycling with fissures that penetrate many metres into the rock. This means that the fissures drain water away from the surface and the water table might be many metres under the surface, lay the radials on the surface and the antenna might well behave as if the radials are elevated. A lot of “mights” there because there are huge variations in the conductivity of rock!

73

Brian G8ADD

23

In reply to G8ADD:

Sure, that is why I am curious about some output of this on air test. Basically we all learned that on HF we care only about AGL height and we dont care about ASL height.

But if you are on a steep rock, you basically imitate antenna on a tower. So a dipole might work better than at home :slight_smile:

24

In reply to OK1BIL:

Now lets try the same with half wave vertical over the same ground. Common >end fed half wave has impedance about 3000 ohms.

3000/(500 + 3000) = 0.85 = 85% radiation efficiency

I have not done many activations but when I have used a vertical I have always used a half-wave vertical. For 20M this does mean you have to lug a 10M pole up the summit and also take along a matching box. However, I have always had very good results and perhaps the half-wave vertical is less susceptible to varying ground effects.

Anyway, if there is an opportunity, I would be very interested in a comparison between a 1/4 wave vertical and 1/2 wave vertical on the same site, same time.

73 Andrew G4AFI

25

In reply to G4AFI:

You actually confirmed the theory described. Half wave can work efficiently even with poor ground. That is why it is very good antenna for /P operations. Providing propper ground to quarter wave can be very difficult even at home. That is why even contesters try to avoid it. But as stated before, 1/4 vertical with elevated 1/4 radials can be also good antenna as it behaves more like vertical dipole which is also said to be a good antenna (C5A used it in CQ WW and won many times).

My recent experience on this topic:

1/4 wave vertical for 40m with 16 burried radials
X
inv vee for 40m, apex 12m AGL, 90 degrees angle (suboptimal)

  • on RX inv vee is S2-S3 better on european signals
  • much less noise in inv vee

The second point shows one more issue about the verticals - anything vertical picks up a lot of noise on lower bands. That is why contesters use beverages for RX and verticals for TX.

26

In reply to G3CWI:

You might be interested in the RBN methodology of a recent test K1JD did comparing a couple of different feed configurations. Follow the thread beginning here:

My conclusion after several activations using both a purely vertical EFHW and a purely horizontal doublet is that I now try to have both antennas available for extended activations. Although the doublet was consistently better toward NE USA and Europe, it was often worse toward Western USA. So far I have no rational explanation for that but I’ve seen the results repeat too often not to believe them.

Looking forward to your results…

73, Bill W4ZV

P.S. Be sure to use multiple RBNs located in different azimuth directions and at different distances. G4ISJ’s post of only one RBN result really doesn’t mean much by itself.

27

In reply to G8ADD:

The interesting thing about a quarter wave vertical with few radials is that if you set it up on a rocky summit you might find a completely different situation to setting it up in your garden.

And how! Last year I made a dual band vertical for 10 and 14MHz based on the design for 14 and 18MHz described by Andy MM0FMF. It worked well on 10MHz in my back garden and somewhat less so on 14MHz, but I couldn’t fathom why and I didn’t have time to dabble with it as it was a last minute project to get me on the air in Portugal.

Setting it up on a rocky summit in Portugal, I noticed three things. Firstly it didn’t match at all on 10MHz. Secondly the match and performance on 14MHz was significantly better than it had been at home. Thirdly - I was getting RF burns off the key!

This year I opted for a simple 14MHz only quarter wave with two counterpoises laid on the ground. I also took an LDG Z-11 auto-ATU to cover any mismatch problems and thankfully it worked fine and no RF burns!

And the reason why I chose a vertical? - to avoid any trip hazards had I been visited on the summits.

73, Gerald G4OIG

28

Variables! They make analysis and comparison very tricky. One of the aerials yesterday was above a partly rocky area with generally firmer ground, while the other was above a grassy area with moist earth beneath. It all has an impact.

Tom M1EYP

29

In reply to M1EYP:

Well you and Richard can repeat the experiment on a regular basis with the antennas in known positions and can compare the results. Yes there will be variations in conditions, but more test data should allow a statistical analysis of the data.

As for the antenna Gerald mentions. I’ve found that I can now look at the ground over which I’m setting up and have a high degree of certainty as to whether it will tune up on the set marks or if it will need some faffing with. The ground in CT3 was significantly different to GM such that I spent some time figuring out how to make it match. That does suggest the antenna is significantly affected by the ground. As to whether it works well as an antenna, I don’t know. I do check RBN to see where I was heard especially if conditions were good and I worked many chasers or bad and fewer chasers. Even when I’ve not been chased at all on a band I’ve still seen RBN spots.

I’ve found that my 12m 1/4GP just works. By that I mean I set it up with the 3 radials sloping from the feed point to the guys on the fishing rod. Every time the SWR indication is the same no matter what the ground is like underneath. Most of the time I have contacts.

I’m looking forward to seeing the first results and further testing from Richard and Tom.

Andy
MM0FMF

30

Just completed a little experiment today to test just how useful the RBN s/n figures are. It was very revealing indeed. Another test required.

73 Richard G3CWI

31

Some RBN measurements:

Test 1: cq every 5 minutes alternating between 11 Watts and 110mW (20dB difference).

Results: never spotted at 110mW despite the reported snr at several stations being well above 20dB when on 11 Watts.

Test 2: cq every 5 minutes alternating between 10 Watts and 5 Watts.

Results: averaging only stations that heard me on 5W and 10W they reported a difference of 1.9dB. However this was only the result of 19 spots on 5W and 12 spots on 10W and I would wish to do this several times before concluding anything about likely errors associated with the RBN.

All the data sets show a certain randomness associated with which RBN stations actually report signals. It’s hard to account for this even on a time varying HF channel.

Before writing up the antenna tests I need to understand a whole lot more about how the RBN responds under controlled conditions.

73 Richard G3CWI

32

In reply to G3CWI:

"…All the data sets show a certain randomness associated with which RBN stations actually report signals. It’s hard to account for this even on a time varying HF channel.

Before writing up the antenna tests I need to understand a whole lot more about how the RBN responds under controlled conditions."

This thread and the forthcoming ‘analysis’ is worth its word count in amusement value.

Mike G6TUH
M.Sc. BA(Hons), GCE, GCSE, CQSW, RSA 8))))!

33

In reply to G3CWI:

Before writing up the antenna tests I need to understand
a whole lot more about how the RBN responds under controlled conditions.

I am one of the quite frequent but intermittent “skimmers” for the Reverse Beacon Network. Skimmers like me do not leave the receiver and PC on line all the time, and, more important here, do not send any spot whenever their equipment if being used for something else.

In practice, this means that comparisons from a station like mine can only be made when you actually have two measures available from the same station. With only one measure, you never know if your signal was not received during the other experiment, or if the OM was just using his station on another band at that moment, or if a local QRM prevented your signal from being decoded properly.

I therefore suggest to eliminate all cases where you do not have at least one measure from the same station in the various configurations tested.

Of course there are many factors that can make any conclusions you draw from such experiments very arguable, but at least the are based on some factual data and not only on subjective impressions.

For what it is worth, I am more than willing to leave my “skimmer” on all day long on 40 meters when you make other experiments like this. Just let me know when it is.

Christophe
ON6ZQ

34

In reply to ON6ZQ:

Hello Christophe,
I agree completely, such factors prompted my post here on the 12th September. A simple test is to co-locate two antennas on the same terrain with a co-ax switch very near the transceiver. The cables would need to be of the same length, size etc. Then switch between the two. Using two radios is not a good idea - leads to different PA variables, receive sensitivity etc.
Mike G6TUH

35

In reply to G3CWI:
The nonlinearity indicated by the two power levels seems unlikely to be the RBN as such, since it merely reports the data from receiving stations. It is more an indication that the S:N ratios reported are not reliable or that skimmmer software requires more than 0 db S:N for reliable logging.

Using software and modes designed for detecting signals below the noise is more reliable. WSJT and WSPR produce more predictable results when you drop the tx power 20 db.

On a related subject, QRSS and long term measurements used to compare two antennas, you may find Owen VK1OD’s reports of interest. There are several related articles and a lot of meat.

http://vk1od.net/grabber/cs07/index.htm

73 de Andrew VK1DA

36

In reply to G3CWI:

Before writing up the antenna tests I need to understand a whole lot
more about how the RBN responds under controlled conditions.

First you need a LOT of data (both in time and from many reporting RBNs) to draw valid conclusions. I’ve been analyzing contest RBN data for several years to compare my signal versus competitors. In contests I’m CQing virtually all the time the band is open to Europe. It’s not uncommon at all to see cycles of 20 dB or more in relatively short time spans.

Below is an interesting post from the Topband reflector supporting the above point. I personally have found instantly switching my K2 between a vertical and horizontal antenna to be more useful.

73, Bill W4ZV

http://lists.contesting.com/archives//html/Topband/2013-09/msg00040.html

I find SNR reports from RBN very useful and RBN a great tool, but you have to
understand the numbers and what they really mean. Let me explain that with a
real life example.

Almost all skywave HF signals are affected by amplitude fading which follows a
Rayleigh distribution when plotted against time.

I recently made a simple test by transmitting an SSB two-tone signal (with the
aid of the two tone audio generator built into the K3) from my EA5 QTH and
monitored the received signal at a SDR (WebSDR) receiver in YO-land on 14 MHz
(2,500 km path). The transmitted spectrum of this signal is two continuos,
equal and constant amplitude carries spaced 1 KHz.

You would expect the amplitude of both signals at the remote end equal at all
times as they are two carriers separated only by 1 KHz transmitted with equal
powers from the same transmitter, same QTH and with the same antenna … Well,
you were wrong

Fading is frequency selective and I found a difference between the amplitude of
both signals ranging from -5 to +25 dB (with a mean of roughly 0 dB) over a 140
second time period. The fact the maximum difference is not symetric around 0 dB
is just random and due to the limited duration of the experiment.

So if I had used single time samples of the amplitude levels from these signals
(the data provided in terms of SNR from RBN), I could have estimated a -5 to a
+25 dB difference between both signals when the average difference is 0 dB.
Remember this is two signals with equal power transmitted from the same TX and
antenna, let alone if signals are originated in different transmitters at
different locations (and so with a different ionospheres between them) with
different antennas and not sampled at exactly the same time instant.

So be careful how you interpret the RBN supplied SNR numbers.

73 de Juan EA5RS

PS: If someone is interested I can supply the recorded audio of this experiment
as well as analysis data

37

So my activation report for Thursday 12th September 2013 on The Cloud G/SP-015 goes something like this:

Picked up Richard G3CWI. Drove to Cloudside and ascended the usual staircase route to the summit. Set up antenna close to trig point, while Richard set up his further along by the rocks.

Called CQ CQ de M1EYP/P M1EYP/P k at agreed intervals on 20m CW - intially every ten minutes, then increased to every five minutes. This was to generate the RBN data to analyse later. In between these operating periods, I wanted to make some SOTA QSOs, so did a bit of S+P’ing on spotted SOTA activations. The results were Caroline M3ZCB/P and Martin M1MAJ/P on Great Mell Fell G/LD-035 and Stephan F/DD6DO/P on Pic de la Journalade F/PE-120. These were all on 20m SSB.

Vlado OM1AX heard me making one of these QSOs and requested a QSO up three for another contact. One of my test 20m CQ calls was answered as well, for a quick QSO in CW. Towards the end of the testing, I used my handheld to call CQ SOTA, albeit still sat on the ground by the topograph! Nonetheless, I added three more QSOs on 2m FM to the log, even though stations were reporting that my signal was lower than usual! All became clear when it was revealed that the VX7R was only a foot above ground level!

I went home and churned out a few comparisons from the RBN data, but this threw up more questions than answers about the charactersitics of the skimmers and software. Experiments continue to shed some light on these questions. For more about that, see above. Or below. Or both.

Tom M1EYP

38

In reply to VK1DA:

Using software and modes designed for detecting signals below the noise is
more reliable. WSJT and WSPR produce more predictable results when you
drop the tx power 20 db.

I’m sure you’re right Andrew. But we have what we have and RBN exists and we can recover the data from it. The skimmers are quite diversely spread for us up in EU, I’m not sure if there are enough at the right distances in VK/Oceania.

This is a piece of amateur radio anyone can take part in. They don’t need to be able to program or build equipment. They just need to go out and operate with the same equipment, same place etc. and collate the RBN data. The analysis can be done by others if necessary. This is one of the reason I don’t want people “cleaning” up their SOTA logs because they didn’t see a * by the QSO. The more data we have, the more we can use that for things we may or may not have yet thought about.

The final results may be that you can’t use RBN for this purpose. But there’s lots of fun to be had finding out!

Andy
MM0FMF

39

In reply to MM0FMF:
Andy,

I’m a fan of RBN and I hope the network expands in Oceania as we have very few skimmers. As you say it is a great adaptation of traditional modes. I know my 20m SOTA stn is working normally when ZL2HAM reports my signal on SOTAWATCH via RBN. Sometimes that is the only report I get on 20m cw.

73 de vk1da

40

In reply to G3CWI:

"It’s perhaps strange that there is little empirical data to allow activators to make an informed decision about which polarisation might perform best over different paths in different situations from a hilltop. "

Any idea for the ETA for your results?

Mike G6TUH

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