Supplied antenna mystery

[bratters]

I have four antennas that I use from time to time; three are Radarbox supplied type and the other is an md 1105 magmount for car use.

I have suspected for some time that one was producing much better results than the others so today I've been running some tests using the same box and with the aerials in the same position.

The results amazed me. Three of the aerials performed virtually identically picking up similar numbers at similar ranges; these were the md1105 and two of the RB supplied type. The other RB supplied outperformed these three by 50% on numbers, though there was only a marginal improvement on distance. Yes, that does say 50%.

Repeated tests only served to confirm the results. The outstandingly responsive RB supplied aerial has a different base design from the others and this is shown in pic. no 2.
This base has three protusions making it easy to identify.

Coincidence? Others no good? Bad testing? Could well be but I'd be very interested to hear from anyone who has a triple knob aerial and can give us some more stats.

[bratters]

seem to have lost a piccy or two

[bratters]

and finally.....

[CoastGuardJon]

Hi John, this is what I've just referred to elsewhere, the one Glynh sent me is the 3 "nib" type, I found the co-ax in your Type 2 is vastly better quality with screening foil and sheath.    I only found this out after dismantling 2 of the others and Glyn's which as reported before, I re-assembled, soldered upproperly (dry joint centre and only interference fit on sheathing, once properly soldered and filled with silicone grease (NOT silicone sealer, who's acetic acid will attack copper) to thoroughly waterproof it, has peformeed flawlessly since.   Just need a good quality stainless steel whip now AN!   I get up to 250 - 260nm with the well screened lead one.

[bratters]

Right Jon. The question is where do you get these triple knib/knob jobbies from?
I have no idea whether these are old or new models and W&S don't have a picture of their "spare" aerial.

As far as I can tell, this knib jobbie will outperform things double the price. But where do we get them?

[CoastGuardJon]

Hi John, I've a feeling they were supplied with the earlier RBs, mine purchased Nov. 2008, Ser. No. 101XX had the plain no nib one, and the one supplied by W&S Oct. 2009 is the same, poorer quality co-ax and lower performanc, of the 50% order you referred to.

[bratters]

Yes Jon, that would make sense in terms of Airnav susequently specifying - or maybe just accepting - a cheaper job, which the plain one clearly is.
My original box was also Nov.08 and that was knibless aerial. I later acquired two more in response to aerials for sale, one of these being the knobby special.

Thinking about it, this is a pretty serious business. I have been happily settling for 30/60 MyFlights numbers over the year when I could have had 60/120. This of course applies to everyone with an RB - if you're lucky enough to have the right antenna then you're in business. If you've got the other one, you're losing out big time.

Could be wrong but that's the way it looks.

No wonder there's a good sale in after-market aerials.

[Jeremy]

Looking at them 2 of the aerials are the same, half wave over a quarter wave,  with the 3rd, 3 section one 2 halfwaves over a quarter wave so the polor diagram will be different. May have more low angle.
Just a thought.
J.

[Wayne]

Morning

I had the three pronged one supplied with my RB when I bought it back in Jan 2008 and I thought it worked well giving me a range of around 110nm. It disintegrated earlier this year and bought another from W&S which is the type 1 in your pictures and I have found that one slightly better than the original. Seems more sensitive.

Wayne

[orkney]

Hi

We had the one without the 3 nibs supplied with our radarbox when bought in June 2009 and were getting a good bit over 200nm with it and that was through our window as well.

It must just be pot luck and circumstances I think.

Claire

[bratters]

Hi John, this is what I've just referred to elsewhere, the one Glynh sent me is the 3 "nib" type, I found the co-ax in your Type 2 is vastly better quality with screening foil and sheath.    I only found this out after dismantling 2 of the others and Glyn's which as reported before, I re-assembled, soldered upproperly (dry joint centre and only interference fit on sheathing, once properly soldered and filled with silicone grease (NOT silicone sealer, who's acetic acid will attack copper) to thoroughly waterproof it, has peformeed flawlessly since.   Just need a good quality stainless steel whip now AN!   I get up to 250 - 260nm with the well screened lead one.

Hi Jon - I decided to test your findings this morning.

I added my own Blue Peter DIY sheathing to a type 1 aerial. 20 minutes of screening with household aluminium foil taped up with insulating tape and WOW -up went the volume of signals received by 30-40% at a conservative estimate. No measurable increase in distance.

I fancy there's even more I can do but for those with the standard dome type RB supplied antenna looking for a cheap quick fix on the MyFlight numbers, get wrapping up that antenna cable. Caveat - it will cost you all of 50p!!

[Fenris]

I suspect that the problem is to do with poor grounding of the cable shield to the ground side of the antenna base. You get capacitive coupling to the metal disc from that, but if the shield is not properly attached then the antenna's impedance will not match the 50 ohm cable and a lot of the energy will then not be transferred to the receiver.

This could be checked with an antenna analyser or a network analyser.

[VK2GEL]

If the better antenna is the one with the disc at the bottom, then this groundplane could be making the difference.

A bikky/sweets tin lid will help, something about 12-18 cm diameter. Some of them can be soldered.

[Roadrunner]

My RB had an areal with the nobs on it - mine is serial 000099 !

Mike

[CoastGuardJon]

VK2GEL both types  use the disc for groundplane, I found the antenna with the three "nibs" moulded to have much better quality (especially the screen) co-ax, which is what I think makes the difference.   It would appear that these better quality antennas were supplied with the Portugese PrimeTech earlier boxes.