Is it worth the money?

[NightProwler]

Well as some of you might know I moved house about a year ago, At my old house I had my good old Imax 2000 up at the end of the garden only about 8 feet off the ground but I worked some cracking DX on that, Then I bought a Sirio GM, Now this is about 6 years back. Anyway up goes the nice new GM and I carry on DX'ing as normal until one night I was chatting to some station in Bristol and for fun I thought I would swap the GM for the Imax and when I did my signal shot up to him. The shiny new GM went behind the greenhouse and I carried on with my old faithfull Imax...Until moving day. No matter what I tried the old girl would not come apart, So with fibreglass splinters in my hands and a tear in my eye I had to hacksaw it up and chuck it out because at 24 feet long I couldent get it in my van. Anyway in my new house Im back on the GM about 20 feet off the ground and it works. But would an Imax work better in it's place like before? I know different antennas and different locations etc etc. Dont get me wrong I would love some metal in the air like an 827 or 2016 or even a Vector 4000 would be nice but it's tricky for me to have an antenna up with groundplanes, I need something that goes up and only up. Well I was blown away by the price of the Imax now, Is it worth the risk? Hmmm

[InTheClouds]

It is really very difficult to say. How much did it shoot up by ? More than an S point suggests a fault with the GM or its feed line. I have used both and they both worked. I preferred the GM myself. The IMAX is a 5/8 wave that believe it or not works quite like the gain master as it has a capacitor in the middle somewhere. It is actually a complex bit of kit. Many use the IMAX as it duals as a 1/2 wave on 15m (hams) so I can understand that choice. Like a GM but does but with arguably a little more matching loss (coils inside coils for tuning etc.). RX noise also seemed a little higher for me on IMAX and I do not believe it was because of greater signals in general. Bear in mind the QTH was very low noise so neither antenna showed any noise signal on RX.

Higher RX noise can be down to RX'd noise off skywave.. i.e. reflected if it has higher angle lobes. And this can happen in some installation types.

Both antennas can be a bit fussy but for different reasons. GM needs to be up high to not unbalance it (then its lower leg of the dipole is up from the ground and should not disturb its balance). The IMAX might be best with some kind of radials/ground plane or at least a decent aluminium pole but there is evidence to suggest an IMAX is not a 5/8 wave GPA (but an end fed dipole). It is 5/8 wave in length for 11m and it might use the coax or pole in part as a counterpoise (or not). Trouble is it is not a normal 5/8 wave so precisely understanding this antenna is a bit tricky. These people seem to know their stuff on the IMAX :

https://www.worldwidedx.com/threads/ima ... or.263435/

20feet and above the GM should be doing it's job. That assumes there is nothing within about a wavelength of the antenna.

Both of these are seemingly a 5/8 wave dipole where all currents are in phase... as opposed to their being a small proportion
of the current being out of phase at the bottom.

Myself stick with the GM. If memory serves correct a 5/8 wave ground plane loses its ground born gain the further it moves
from the earth. (which provides a ground reflection) but it needs a good ground plane radial set... think 16 - 30 to ground mount.
An elevated 5/8 wave GPA ideally has radials as well... i.e. a normal one. But as the currents are in phase and the IMAX current centre is in the middle
the radials may be doing less as the current at the physical feed point is lower on the IMAX. In short where there is high current on an antenna
feed point radials are required to produce greater efficiency. (Think 1/4 wave where feed point current is at maximum, without 4 radials the antenna is a poor performer)

I say stick with GM ! Others may have different views.

[InTheClouds]

Also another thought that springs to mind this morning is interaction between the 2 antennas. A 3 element Yagi is made by adding a director and reflector element to a dipole. As such unless your 2 antennas are separated by many wavelengths they could interact differently with each other respective to TX/RX direction.. metal in the air close to your antenna in use may affect the phase of the waves arriving/being sent from the current antenna in use.

For example in one direction it may dB a few dB up and another a few dB down. That might explain what your friend saw on his S meter.

Did you get a corresponding increase or decrease in RX signal from your local station ?

There are many factors related to physics as to why one works better than the other, possibly even combinations of factors.

There are probably more GM users than any other antenna, especially on CB, that speaks volumes.Hams seem to like the IMAX (or MAX2000 as they are called)... as explained. When these antennas are both well set up they will both work well. I think the GM wins out in my own experiences.

And I take into account what CB users do as much as hams (I am a ham). Some hams still plonk an antenna on the ground and think that is a good antenna.Whereas an elevated version of the same antenna would beat it hands down. The reason why they ground plonk is that is they have no other choice. Even multi band options tend to be rather long for the lower frequencies hams often use... so ground plonking is the only option.

GM should do you fine... if you can get it up higher safely all the better. Enjoy your set up.

[The Collector]

2 pairs of "Stilsons" are sometimes needed to get those brass joints apart. I had to use some on my old Antron in the late 90's when it came down. It does put a few marks on the chrome plating though if the joint is well stuck.
Pre-soaking with WD40 or similar penetrating spray is advisable too, a few days in advance (and redone on a daily basis until the Stilsons are used).