Fitting a Sigma Boomerang loft aerial achieving low SWR

[Lefty]

Hi, I am a newbie having my last home rig 40yrs ago and the guy who I bought it off fitted for me.
Now I have bought myself a Thunderpole T800 with a Sigma Boomerang loft aerial.
I have a decent sized loft as I am the top flat with two below me. We had our 1st dry run of trying to position the aerial in the loft but the SWR was higher than the set position on the meter. My friend who is a precision engineer which although he knows nothing about CB radios he is a quick learner and skilful at thinking his way out of situations. However I do need some advice about how to position the Sigma Boomerang aerial to get the SWR down or I will have to try another aerial. My friend after gong back and reading about the aerial believes he has clamped it the wrong way round on a block of wood he was using to move the aerial around in the loft while I was doing the SWR readings. I can't see what he is doing in the loft due to my disability but visulise in my head that it should be clamped as high as possible in the loft with the thinner more whip type aerial pointing as vertical as possible making the thicker shorter aerial being more horizontal. Also we are working with alot of coaxial cable which I am beginning to think is not helping the SWR.
Any advice would be most welcome. Also suggestions for easier loft 'single' aerials if we fail with the Sigma Boomerang.

[NoName]

Page 5 and 6 here https://www.sirioantenne.it/images/pdf/ ... _serie.pdf

[rhythmstick]

That pdf ^^ shows which way up the antenna should be mounted, so I would get your friend to double-check that!

Also, if he has a multimeter, I would ask him to temporarily disconnect the coaxial cable at both ends to ensure there is infinity resistance between the inner and outer conductors. If there is just a single strand of copper connecting the two, that could be the reason for your bad SWR.

Also, the position of the antenna is really important. It's a shame if you have to settle for a loft installation (rather than something on the chimney or outside wall), but I would try and keep it as far away as possible from the roof and any other objects in the attic.

Also, if your coaxial cable is much longer than necessary (and you don't plan to move the antenna or radio to somewhere further away), I would consider reducing the length of the cable.

I'd also check it is 50 ohm cable (not 75 ohm). It should be printed on.

Finally, I'm not sure how you tune those antennas, but if you have a very different SWR reading on channel 1 than you do on channel 40, then that would suggest you need to tune the antenna itself.