Is the (I) Max 2000 just a 5/8 like the A99 is just a 1/2 wave?

[wavrider]

Someone ( I think Marconi and other members of the forum) Tested the Gainmaster and said the best results where in the clear away from any structures.

Gain master being center fed type antenna may not work so well mounted low and to a metal gate.

The I2K being an end fed would probably outperform the GM but give it a try maybe it will work great. Stranger things have happened.

 

[RadioDaze]

Thanks, yes wavrider... plans are afoot for next time I go out. I will test the GM bolted direct to the gate... (I do wonder if the choke would help it "not see" the gate.) Or whether that is irrelevant and that the proximity of the large steel framed gate will skew the resonance/loading impedance and affect just about everything performance wise.

Just as a point of interest I have had a QSO to Indonesia (from UK) during the winter time with the Gain Master 3m off the ground (100W) using a tripod so it does seem to work given a good set of atmospheric conditions.

It remains to be seen if the gate will cause bad SWR in the first instance. I will try it and then start adding poles under it to see what happens. This of course will give no information about how it affects the GM elevation angle as a good DX antenna but will at least let me know what I can and cannot do practically whilst keeping the SWR low.

This is really about a balance of speed of set up in a mobile static scenario vs performance compromise vs saving money on not buying the IMAX if I do not have to. (happy to do so if the GM does not SWR well but I owe it to myself to find out before I start splashing the cash.. over here the IMAX is equivalent to $160.00

 

[The DB]

I'm sorry DB!! I thought that was CK giving the poster help lol!! It's early!! Gots to get me coffee!!

Not a problem.


The DB

 

[wavrider]

WOW on the expensive side across the pond.

SO with that said many amateurs in the UK use fishing poles to build verticals with wire taped or zip tied to them, and also use wire for ground radials, so maybe a home brew vertical is in the future?

Less expensive than the I2K which is really nothing but wire and a lossy matching network

 

[RadioDaze]

Well I tested it tonight and the SWR was 1.3:1 on the T5 and on 2 poles 1.2:1

So I need not buy an IMAX it seems I am surprised it SWR'd in so nicely. Happy with that, not sure about angle of radiation but with weak skip I spoke to Poland, Spain, Brazil and plenty of Sporadic E UK stations (Stornoway Scottish Island of Lewis about 500 miles from me) And 3-4 stations on line of sight within 200 miles (they were also at height approx 200-300M)

It works !

 

[wavrider]

Good deal glad you got to make some contacts.

thanks for posting the results of your testing

 

[Road Squawker]

Fair warning, this might get a little complex... You have been warned...
Long story short, yes, this "magic" common mode current resistant length(s) exists, but in the real world, it is nearly impossible to calculate to any degree of accuracy...


The DB

... and once you have calculated the "magic"length,then change frequency,......................and throw all the calculations away.

 

[RadioDaze]

Yes indeed, I was happy with the performance it put in. I managed a 88mile line of sight contact to a mobile static station 230M ASL (I was at about 165M) using just a Sirio 5000 on a mag mount which is not a huge distance but I gave an S-5 at the other end and got an S-0 Radio 5 back.

Saved me some money and shows that even if it is not 100pct optimal the Gain Master cracks out quite well with a large amount of steel directly attached to the base.

I would love to have been able to see the RF elevations and plots live on that gate compared with how I usually set it up.

*Imagine a live RF video camera which showed your elevation lobes and ground losses as 3D coloured graduated XYZ image. That would be the quintessential RF tool, an enthusiasts dream.

I hope to catch some of your guys from the US and beyond on this winter when the F2 once again opens over the Atlantic : )

I will be sitting in my car freezing so I can hear you, and you know what I look forwards to it greatly. Lots of tea in flasks and loads of clothes on : )

Listen out for "Two Six Sierra Oscar Two Three Nine" - 26-SO-239 (as per the socket on the back of your radio, an easy one to remember ! )

Thanks for the valuable input guys.

 

[RadioDaze]

Does anyone know the mechanism by which the GM seems not to respond negatively (at least by SWR reading) to a large metal body below it given it is seen electrically as a centre fed 5/8 dipole. I was wondering if the choke is important in this effect ?

(It beckons the question of what SWR actually is I must check it's relationship to resonance and impedance)

I think the GM is a truly exceptional antenna design. I am hugely impressed by it whenever I throw it a curve ball it hits back with impressive performance.

 

[Needle Bender]

My GM didn't care where it was mounted or onto what when SWR was the consideration. I could seem to force it to present a bad SWR, it was the performance which suffered greatly from having another antenna in it's near field.

Just bring along a 6m mast to put below it.

 

[RadioDaze]

Appreciate your observation needle bender but the goal of bolting it to the gate is to speed up set up time in winter months where handling the least amount of metal pole is desirable.

I can of course wrap up well clothing wise and on occasion I will go the whole hog with the 6m of pole (on low wind days) but sometimes I want to have a nice swift set up for a 2-3 hour DX session.

Being mobile static sometimes I plan for a nice long 6-7 hours with all my batteries fully charged and have a long one but in the mid winter I think that might be a bit uncomfortable whatever I wear. I am not a man to run his engine and pollute the environment unnecessarily to keep warm so need quick set up when it is typically between 3 and 7C on a typical UK winters day.

This was the reasoning for Gain Master gate testing last night. Performance could well be down in absolute terms if we consider radiation angle but it may well still be better than just a 1/2 wave bolted to the gate. In any event still very pleased how it SWR's up with is hurdle 1.

The big question is would the IMAX which by design is a ground plane antenna (not that Solarcon would inform you of that as they sell it with no radials as standard) be better in terms of low angle radiation bolted on the gate directly. The only way to really know would be a direct test to 2 or 3 local stations put one on and taking it down and putting the other on. Unlikely to happen so I will stick with the GM.

 

[222DBFL]

If it works, run with it and use it!! Make contacts! It's not always about having the most efficient setup one can have especially being static mobile. If it is working and you are making contacts and vswr isn't bad, then just have fun as that is what it's all about in the end to me anyway. Yeah it could be better I'm sure, but is it ideal for your situation like you stated. Just use it!! That's JMO.

 

[RadioDaze]

For me a big part of fun is knowing that I have the best performing set up given the practical situation of use. Then I am not left wondering: "I wonder if I would have got through if I had a.... blah blah blah set up"

It is a valid point I think I will just crack on as it does indeed work quite nicely, surprisingly nicely.

 

[vkrules]

Actually i think you will find the gainmaster to be a "very happy bunny' bolted to the gate . By design it is isolated from the mount ,has no problem with cmcs and produces a nice clean pattern in most situations. What it doesn't like is metal along side the bottom coil (choke).
P.S I spent weeks running side by side comparisons with the Imax and GM . I tried heights from ground level to 60 feet and several different locations.Sold the Imax and wont be buying another.

 

[RadioDaze]

Good to know thanks for the input. Just cam in from a 2 hour gate post GM session. Funnily enough calling 41/43 div exclusively. Fair sure I heard 1 Australian/Kiwi accent at S-0 coming back from a QSY.

I QRZ'd but could only hear hiss, must have been exceedingly weak and random short opening or I simply misheard. It had that "other side of the planet" quality.. that almost ghostly distant weak station... with that almost "doubled up/slightly echo-ey" sound.

Actually that spurs an idea for another thread.