Topband: INV-L with traps

[DAVID CUTHBERT]

Cris,

your VSWR measurements point to a system loss resistance, referrred to the
antenna feedpoint, of 5 to 10 ohms. This assumes that the matching
transformer is working well. The radiation resistance of your antenna on 160
meters is a bit under 14 ohms.

Can you tell me the VSWR bandwidth? Such as between the 2:1 and 3:1 VSWR
points? To eliminate the matching transformer from this puzzle can you also
take measurements without the transformer?

    Dave WX7G




On Thu, Oct 8, 2009 at 11:50 AM, cris blak <cyo3fff at yahoo.com> wrote:

> 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
> >
> >
> >
> >
>
>
>
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