1. Yes, pulled it out all the way. It just wouldn't dip lower than around 29.200 with the tip all the way out. I have the 20m and 40m version of these antennas so I know how to use and tune them.
2. It said 28 MHZ on the package and on the base of the antenna.
Theo
Lengthen the tip or if this is not possible add some insulation sleeving or PVC tape over the tip and / or top part of the helical coil. This will lower the resonant frequency a bit and may be enough for what you need.
Theo
By the way if you ever find you have a helical whip and you can't get it to go high enough in frequency put some shorted turns over the helical winding. Biggest impact is when near the top of the whip. Slide up and down to fine tune. This is what the rings you often find on helical whips are.
VK7HH wrote:
If you have access to an MFJ analyser or something you can measure your coax. Remove the antenna and measure with an open end. X should not equal 0 near the frequency of operation.
Hayden
I just had a chance to take that measurement. See below.
Before doing anything though I put it on my mount as it is and thought I'd put it through the antenna analyser to see what it said expecting to see a dip somewhere on 27 MHz. What I found was a dip at the low end of 26 MHz but the SWR only dipped down as low as 2.2:1. The only other dip I got was at around 28.2 MHz but the SWR only dipped to around 3:1.
So, idea's anyone? Do I need still look into my coax length, or do I need to try improving my grounding?
Hi Theo,
Was the 27MHz Jaycar whip put on the existing base that you've been having issues with? What happens if it's put onto another base instead?
Your measurement into an open end on the meter says that X is 47.3, so going by that photo it suggests that the coax is not near an electrical quarter-wave length long, or multiple thereof. What happens if you do the same measurement, but with a shorted end? Just curious.
VK7HH wrote:Was the 27MHz Jaycar whip put on the existing base that you've been having issues with?
Yes
What happens if it's put onto another base instead?
My boot has two bases installed, both gave similar results.
Your measurement into an open end on the meter says that X is 47.3, so going by that photo it suggests that the coax is not near an electrical quarter-wave length long, or multiple thereof. What happens if you do the same measurement, but with a shorted end? Just curious.
Will try that when I get a chance. Any ideas how to easily and effectively short out a SO-239 base?
VK7HH wrote:Was the 27MHz Jaycar whip put on the existing base that you've been having issues with?
Yes
What happens if it's put onto another base instead?
My boot has two bases installed, both gave similar results.
Your measurement into an open end on the meter says that X is 47.3, so going by that photo it suggests that the coax is not near an electrical quarter-wave length long, or multiple thereof. What happens if you do the same measurement, but with a shorted end? Just curious.
Will try that when I get a chance. Any ideas how to easily and effectively short out a SO-239 base?
Jam a heap of wire in the center pin and wrap it around the outside?
Do you have a 5/16" to PL259 adapter you are using to put the 27MHz whip on the car? Has your analyser been tested on another known good load (i.e. a dummy load?).
Suggest you plug in a good dummy load where the antenna goes and measure the result. (I am presuming the base is a SO239). This will verify if your coax is OK.
Before you start cutting the whip I suggest you wind some hook up wire over the helical near the top. Short these turns. Fine tune by moving the shorted turns up and down the whip. Use this method to get the antenna on frequency. This will avoid you cutting the whip. Once you have verified you can get the whip to tune then you can attack the whip but I would cut the wire and not the fibreglass rod so that you can rebuilt the antenna if need be.
From what I can see you most likely have an earthing problem. Try some lengths of wire as radials connected to the antenna base to see if they change the situation. If it does it would indicate that earthing is a problem.
Coax length should not matter unless you are using this to form part of your matching system which is not a good idea.
