Topband: INV-L with traps

[cris blak]

Hello all,

Last weekend I succeed to install the two traps on my 160m INV-L to be used on 40 and 80m. The traps are made by RG58 coaxial cable wind up on 40mm plastic pipe. The 40m has 11 turns and the 80m one, 21 turns. Each of theme were checked on the bench for resonance and it did resonate on those bands.
First, I install the 40m one. The first wire segment were end up at 7.5m having the best 1.6:1 VSWR on 7040KHz. I mention that the antenna is made by 2.5mm polyvinyl isolated copper conductor. The measured velocity factor were about 0.85. There wasn't a way to improve the VSWR.
After that, I install the 80m trap on a 8.5m wire segment between the traps. The best VSWR on 80m were 1.6-1.8:1. No way to improve it. I mention that before, on 160m the VSWR were 1.1:1 on 1840KHz. The antenna were feed with a 50ohm coax through a 2:1 toroidal transformer to adapt its 36ohm.

The point is the overall antenna efficiency!
I have an inverted V for 160/80/40m with 12m apex which is working fine on all those bands.
I compare the INV-V with the new INV-L on 80 and 40m. For almost all the signals, local or DX, the INV-V has at least 6-10dB + in front of INV-L which is huge. First, I thought that this difference is because the low angle of the INV-L but no. Even on a VK, UA0, JA, K or ZS station, the INV-V were the best.

I think something went wrong or this simply, this is the quality of such antenna!?!
If one of those who have or built such antenna and compare it with a half lambda dipole (INV-V or else) or a quarter wave monoband vertical could confirm or denied this fact.

I'll try to built another traps with a L/C components. In this way, I have another question. What is the best L/C ratio or putting in another way, what is the best L and C to be used for such application.
Is it a good goal to have a coil as short as possible using high capacity to compensate on the resonant frequency?
For example, for 7MHz trap, I think a good solution will be an 470pF dor knob capacitor along with an air wind coil of 1.1uH with high Q factor. Zseries of this circuit at 7MHz will be 0.005ohm and the parallel one, about 7.8Kohm considering a 0.3ohm as a loss resistance. The overal Q will be about 161. The same circuit on 3.5MHz will have Zseries = 73ohm, Zparallel = 32ohm and a Q = 81. On 160m, Zseries = 172ohm, Zparallel = 14ohm and Q=42.

Look forward for a guidance toward gaining the best results with such approach.

Thanks.

73 de YO3FFF
Cristi

--- On Fri, 9/25/09, cris blak <cyo3fff at yahoo.com> wrote:

> From: cris blak <cyo3fff at yahoo.com>
> Subject: INV-L with traps
> To: topband at contesting.com
> Date: Friday, September 25, 2009, 4:08 PM
> Hello,
> 
> I have an INV-L for 160m which is working fine along with
> its 30 radials. The vertical part is about 16m. I intend to
> add two traps in order to use it on 80m and 40m. Is there
> anybody who use such a design for DX (meaning "in
> practice"). 
> What is the difference in terms of quality between an 160m
> INV-L and an 160m INV-L with trap or traps (80/40m)? 
> I already build the traps for 80 and 40m with RG58 coaxial
> cable and tune it with my miniVNA. The Q factor is around
> 20.
> 
> Thanks for any advice/ report.
> 
> 73 de YO3FFF
> Cristi
> 
> 
>       
>