Antenna swap observations 1/2 wave to mobile whip

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InTheClouds
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Antenna swap observations 1/2 wave to mobile whip

Post by InTheClouds »

I had great trouble getting back to the Euro DX with a 1/2 Silver Rod static mobile a few days ago, I heard them great S7/S9's. I could not get back around 15 calls/responses, nothing........ like my set up was broke (but all working) I swapped to a metal to metal mobile antenna 1.7M, bang, first call guy from Ancona Italy (albeit at a S3 to S1 with some QSB) I have 1.2:1 SWR on both antennas so no issues there.

Same swap, the other day to someone 15 miles away, local contact my RX went from a S7 to a S1 - 6 S point drop in my RX. And I dropped 4 S points to him.

Of course different contacts entirely but still very interesting.

So for the DX either conditions changed in those 4 mins it took for me to swap antenna, or the mobile antenna put energy out at the right angle to get the DX that was prevalent. The local contact signal loss was more anticipated. ( A total of 10M of metal in the air vs 1.7M)

I did some very crude diagrams and came to the conclusion that you need some energy going out at 19 - 25 degrees to catch the Sporadic E based on the facts the E layer is about 62 miles up above us and the max expected hop could be 1,400 miles with an average for my own contacts seemingly at 800 miles.

I cannot for the life of me understand why the Silver rod was so incredibly poor at getting back to many stations from Europe at that moment, I was hearing Italy, Spain, Sweden, Denmark,Poland etc and they could not hear me for love nor money.

It seemed that other UK stations suffered a similar fate except for those with beams that I could hear, though still speaking of QSB. In conversation with a couple of locals they mentioned that the Euro stations were possibly hearing each other better than us and so we just could not crack through with verticals. I was also running just radio power and I appreciate 100W seems like the normal DX power for most stations to cut through a bit better. (Though it did not explain why I could make an instant contact to Ancona when I swapped to the mobile whip)

The only other thing I could think of is at this QTH my main energy was going out lower say example 9-15 degrees and maybe there is some "lobal" break up creating a null at some take of angles. (i.e. not uniform energy at all angles akin to a donut and instead rather spikey.) Though the antenna is earthed well on 4.5M feet of pole, fed with 213 and is ugly balun choked so it should be ok in theory)

One thing is for sure it is very interesting and it seems bigger is not always better for E layer DX (summer Euro skip).

I know DX especially is more random than scientific but I do like to try and understand what I can potentially have influence over.
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Re: Antenna swap observations 1/2 wave to mobile whip

Post by Mudslinger »

Which silver rod were you using and how did you mount it?

I have found that unless they are mounted on a decent sized pole and they are more than 10 feet from the ground they can perform very badly.
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Re: Antenna swap observations 1/2 wave to mobile whip

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5 meters, Sirio GPS27 so getting close to 1/2 wave, on "ground wave" or line of sight it works superb static mobile and I have noticed it works a little less well very low down i.e. 1m for line of sight. It is difficult to put it down to anything other than odd conditions. Usually if I hear them I can talk to them, but this was a strange evening. One other theory is my radio may have a generous RX needle (LCD) and peaks people more S points than they really are as I was on radio power alone I just could not cut through.

I have some other theories about the local contact drop off (my RX) when I switched to mobile whip. I would of course expect a drop but 6 S points seems like a huge drop to me. I had structures around me that may have contributed and my whip mount position meant the whip would have been slightly more directional in the opposite direction to the local contact, this may have added a 2S point extra drop off.

All just joining dots together really, no certainty in these thoughts. I try and work stuff out logically if I can but can never be sure with the invisible force we all deal with ! :lol:
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Re: Antenna swap observations 1/2 wave to mobile whip

Post by The Collector »

Lack of stations hearing you could've been down to them running 500watts whereas you were only running 100? I don't do DX'ing so I'm just guessing from what I've seen happen on UKFM. Sometimes you can get the bounce right and go thousands of miles on just a few watts.
As you mention, your aerial's radiation angle may have been different to theirs, so maybe a 5/8th wave may have made a difference...it's a hard thing to pin-point exactly. The right "lower" angle of their aerials perhaps hit you right, but yours literally skipped past them or stopped short.

Perhaps a test between a 1/2 wave and a 5/8th wave with an antenna switcher on them for speed would perhaps tell you. You could flip between them for the best results on TX / RX. Bit expensive though ;)
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Re: Antenna swap observations 1/2 wave to mobile whip

Post by ch25 »

You can't have too many antennas...
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Re: Antenna swap observations 1/2 wave to mobile whip

Post by InTheClouds »

Thanks all and Ch25 whilst any given QTH may respond a bit different this is a good starting point, thanks for that article. For line of sight I will go upwards and for DX I can experiment between between 0 and 3 poles (1.5m each) and see if this has an impact. If all of a sudden I am not getting back I will adjust my poles to see if there are some gains to be made. :thumbup:

I also now consider that these 2 antennas may have interacted with each other. (I only screwed my whip in when things were not going well with the Silver Rod.) But the whip RX/TX pattern might have been also affected by the Silver rod sitting up there. Now I think of it, it would be a surprise if a almost perfectly resonant conductor was not having an impact on surrounding RF fields. :lol:
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Re: Antenna swap observations 1/2 wave to mobile whip

Post by The Collector »

If your silver rod was close to your car, that may also have dragged your signal slightly towards it. It may need to be further away (30ft???).
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Re: Antenna swap observations 1/2 wave to mobile whip

Post by InTheClouds »

Good point The Collector, although that would be largely in the direction of intended travel at this QTH, but as you mention all surrounding objects including vehicle will have some kind of effect on the local RF fields coming in and going out.

Reviewing that article Ch25 there are many practical issues with it. The first is the model uses 5.5M ground plane radials, rare(though at the end it does mention any number or type of radials to be fair). At ground level you can have SWR issues (objects close), noise issues, greater ground losses, 1/2 wave CB verticals never ship with any useful radials, you could count a pole as a counterpoise but at ground level there would be no pole, this explains Mudslinger's experiences. And last of all most people cannot erect an antenna at 16.5M high (1.5 wavelength for us Cb'ers). It also mentions..

"between 0.25 and 1.25 wavelength. At those levels above ground most of the energy will be radiated at angles of 27° to 45° into the ionosphere."

Which is arguably not far from where you want it for some Sporadic E, at least 27 degrees may have purpose for short hop, although of course you don't want to waste a lot of RF at the wrong high angles. I do wonder this article had F2 layer long haul DX in mind.

However the principles can be held in mind and it does suggest to change the amount of pole-age if you are not getting the Euro DX which may alter your radiation angles, that is surely worth a try. There is always a sweet spot between the theory and practicality at the QTH and it is easy to see why, "get it as high as you can" generally works for home base.

If something is not working out, changing it is worth testing. I am going to do more tests with the mobile whip with no Silver Rod in the picture.

One final thought relating to this statement: "At 0.25 wavelength the main lobe at 15° is somewhat more flat." that seems to be quite good if the "main lobe" is 15 degrees as stated...but seems a bit contradictory to this statement:

""between 0.25 and 1.25 wavelength. At those levels above ground most of the energy will be radiated at angles of 27° to 45° into the ionosphere.""

So where is the main lobe ? 15 degrees or somewhere between 27 and 45 ? It cannot be both.

0.25 (2.72M for us) seems like it could be just about right for E layer DX. I will give this a try for the summer DX for sure.
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Re: Antenna swap observations 1/2 wave to mobile whip

Post by InTheClouds »

Did a quick bit of DX this afternoon, going back out this evening after din dins. 1.7 M whip the only antenna I had with me, nice high spot. Plenty of Scotland, Ireland, N.Ireland contacts 5 by 9 all the way stable contacts, also a nice one into Gibraltar - Mainly a S0 R4/5 mod to me peaking at a S4/5 at times. So this whip works, I look forwards to doing more tests with it this evening and beyond. I am very much getting the feeling a well installed mobile antenna will do as well for these max 1,400 mile E Layer contacts in the summer, Gibraltar being a around 1,100 miles.

I have a metal to metal mount, sanded all the contacts and earth bonded relevant panels, feed it with Mini8 Coax with a 5 turn ugly balun before feed point, trimmed it to SWR 1.1:1 - so far so good.

The downside is that it won't line of sight as far for long distance point to point as a home base antenna.
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Re: Antenna swap observations 1/2 wave to mobile whip

Post by InTheClouds »

Out again today 1.7M whip doing nicely, Germany, Norway, Scotland, Spain, Italy and Serbia, seemed to be a very strong opening between Denmark and The Netherlands, Copenhagen coming in a stable S7 for some hours at the QTH, but no way I could get back (neither could any other UK station so E layer prop can definitely be a one way phenomena) It does feel like you are more exposed to strong RF fields though with a antenna fixed to the body of the vehicle compared to a vertical on a pole 7-8 meters away, simple proximity suggests that, so I feel using a pole based antenna for summer skip does have that going for it.
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