Topband: Topband loading coil

[K4SAV]

If you got an SWR of 1.2 on 160 meters from an 80 meter inverted L, you 
had a lot of loss either in the radial system or in the loading coil.  
The resistive part of the feedpoint impedance of that antenna on 160 
should be very low, maybe about 4 ohms plus radial system loss.  Exact 
number depends on antenna details.  Sounds like you made a more 
efficient coil and the SWR went up, which it should.

Jerry, K4SAV


On 6/6/2015 7:49 AM, Max Cotton wrote:
> I have an inverted L antenna resonant on 80m, I decided to add a loading coil to the base to bring it on frequency for TopBand. I wound a 2.5mm wire coil 16 turns on a bit of square Paxoline board by drilling holes into the board each side and feeding the coil through the holes, a bit of a struggle but it worked, not very pretty, it is 146mm diameter and 120mm long 30.5uH. When I first tried it the SWR after small trimming was 1.2:1 band centre and 2.0:1 band edges. Now it looked a but ugly, so I decided to neat it up a bit by adding two fibreglass webs so the coil was now  circular and held by a cross section instead of just the one plane,  now when I retried the SWR it is still resonant on 1.800 but the SWR is now 2.0:1 in the middle of the band and 4.0:1 at the edges  the turns are the same, the inductance is the same but I have lost my fine SWR curve. I only added the fibreglass and neated up the coil, Ideas what to do next apart from removing the fibreglass webs and goin
>   g back to ugly coil?73 Max M0GHQ 		 	   		
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