[Elecraft] Off-Topic: Your advice/suggestion about antenna

Bob McGraw K4TAX rmcgraw at blomand.net
Fri Mar 13 20:28:17 EDT 2020 

Just to set the record straight.

dBi = dB(isotropic) – the forward gain of an antenna 
<https://en.wikipedia.org/wiki/Antenna_gain> compared with the 
hypothetical isotropic antenna 
<https://en.wikipedia.org/wiki/Isotropic_antenna>, which uniformly 
distributes energy in all directions. Linear polarization 
<https://en.wikipedia.org/wiki/Linear_polarization> of the EM field is 
assumed unless noted otherwise.

dBd = dB(dipole) – the forward gain of an antenna 
<https://en.wikipedia.org/wiki/Antenna_(electronics)> compared with a 
half-wave dipole antenna <https://en.wikipedia.org/wiki/Dipole_antenna>. 
0 dBd = 2.15 dBi

dBiC = dB(isotropic circular) – the forward gain of an antenna compared 
to a circularly polarized 
<https://en.wikipedia.org/wiki/Circular_polarization> isotropic antenna. 
There is no fixed conversion rule between dBiC and dBi, as it depends on 
the receiving antenna and the field polarization.

dBq = dB(quarterwave) – the forward gain of an antenna compared to a 
quarter wavelength whip. Rarely used, except in some marketing material. 
0 dBq = −0.85 dBi

dBsm = dB(m²) – decibel relative to one square meter: measure of the 
antenna effective area 
<https://en.wikipedia.org/wiki/Antenna_effective_area>.] 
<https://en.wikipedia.org/wiki/Decibel#cite_note-60>


dBm−1 =dB(m−1) – decibel relative to reciprocal of meter: measure of the 
antenna factor <https://en.wikipedia.org/wiki/Antenna_factor>.


73

Bob, K4TAX


On 3/13/2020 6:08 PM, David Gilbert wrote:
>
> Lyn,
>
> A dipole over ground has considerably more than 2.14 dbi maximum gain, 
> and since you said you had a tree in the middle I assumed (probably 
> incorrectly) that it was enough in the middle to allow a 40m dipole to 
> fit crossways your lot to other trees.  If that isn't the case, OK.
>
> You didn't say whether your model that gave you 4.7 dbi for the EDZ 
> was a free space figure (and I'm too lazy to model it myself now to 
> check), but if so yes ... there would be at least a 2.5 db benefit to 
> the EDZ.  I've done my own tests to demonstrate the clear advantage 
> that even 2 db can provide (see 
> http://www.ab7e.com/weak_signal/mdd.html), but I still wouldn't call 
> that "far outperforming".
>
> And who said anything about putting up a rotating yagi??  Your EDZ is 
> not rotatable so why eliminate a wire yagi from consideration because 
> it isn't.  As I said, you do have to settle for unidirectionality but 
> your original comment was that other wire options would beat the yagi 
> for gain ... they don't.
>
> I've read your reply three times now and still don't understand what 
> 20KW into a ten curtain array has anything to do with this discussion.
>
> Dave,
> AB7E
>
>
>
> On 3/13/2020 12:49 PM, Lyn Norstad wrote:
>>
>> Dave -
>>
>> I actually /do/ consider 4.7 dbi as "far outperforming" 2.14 dbi 
>> (ordinary dipole).
>>
>> And since cost is an issue for some of us (along with HOA 
>> restrictions), I rejected the idea of getting a couple extra dbi at 
>> the cost of many thousands of dollars.  And adding a N-S 40m dipole 
>> fed at the same point would have required either traversing my 
>> neighbor’s yard, or erecting a 2 towers … neither of which is feasible.
>>
>> And forget the logistics of erecting a 2 element beam for 80 meters 
>> (see OptiBeam OB2-80+ with 74 foot elements on a 36 foot boom), tower 
>> and rotor for that monster.
>>
>> We have a commercial (HST) shortwave station a few miles away that 
>> runs a 20kw transmitter on various 7 - 10 MHz frequencies into an 18 
>> dbi gain "curtain" antenna aimed over the pole to Europe.  Their beam 
>> width is 38º.  Ten curtains could be hung using relatively 
>> inexpensive towers or masts spaced at 36º in a circle.  The 20kw 
>> input results in an ERP of 808 KW, according to their FCC license, at 
>> an extremely low angle of radiation, and very low maintenance.
>>
>> That would actually be my first choice.
>>
>> 73
>>
>> Lyn, W0LEN
>>
>> -----Original Message-----
>> From: elecraft-bounces at mailman.qth.net 
>> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of David Gilbert
>> Sent: Friday, March 13, 2020 1:39 PM
>> To: elecraft at mailman.qth.net
>> Subject: Re: [Elecraft] Off-Topic: Your advice/suggestion about antenna
>>
>> That is certainly a perfectly viable antenna and probably a fine choice
>>
>> for your needs ... but it does not "far outperform" either a dipole or
>>
>> especially a 2 element yagi at the same height. (although the yagi would
>>
>> of course be unidirectional).  4.7 dbi is dipole territory.  You could
>>
>> have gotten pretty much the same result with an E-W 80m dipole and a N-S
>>
>> 40m dipole fed at the same point (orthogonal fan dipole).  And assuming
>>
>> you used capacitors for the EDZ, dipoles are easier to build.
>>
>> 73,
>>
>> Dave   AB7E
>>
>> On 3/13/2020 11:19 AM, Lyn Norstad wrote:
>>
>> > Duane -
>>
>> >
>>
>> >
>>
>> >
>>
>> > I am of the mind that the antenna is the most crucial part of any 
>> station,
>>
>> > and probably the most often maligned.  I have made a number of 
>> presentations
>>
>> > to ham groups on the design and construction  process involved in 
>> getting
>>
>> > the most bang for the buck, depending on your wants and needs 
>> (everybody's
>>
>> > are different).
>>
>> >
>>
>> >
>>
>> >
>>
>> > In my own situation (2 acre semi-rural lot approx.150 feet x 600 feet
>>
>> > running E-W feet, and active HOA) the goal was to have a single 
>> antenna that
>>
>> > would provide the best primary signal on 80 meters in a North-South
>>
>> > direction, while providing the best possible signal on 40 meters in an
>>
>> > East-West direction, consistent with the 80 meter performance and 
>> without
>>
>> > unduly provoking the HOA (or my XYL).
>>
>> >
>>
>> >
>>
>> >
>>
>> > I decided on an Extended Double Zepp, cut for 3.5 MHz. That 
>> resulted in a
>>
>> > length of 360 feet, which worked nicely since I have 400 feet clear 
>> from the
>>
>> > house (West end) to a perfect tree for the far East end. And 
>> another tree
>>
>> > in the center for support of both the antenna and the feedline.
>>
>> >
>>
>> >
>>
>> >
>>
>> > I am feeding it with a 160 foot length of 600 ohm "true ladder 
>> line."  I can
>>
>> > go into more detail if this sounds like something that would work.  
>> Modeling
>>
>> > this antenna with EZ NEC shows a maximum theoretical gain of 4.7 
>> dbi in both
>>
>> > North and South directions.  With the ladder line, a dual hybrid 
>> balun and
>>
>> > short length of coax into the shack, my KAT500 tunes it very nicely 
>> on all
>>
>> > bands 160 m thru 6m.
>>
>> >
>>
>> >
>>
>> >
>>
>> > I don't have your call so can't see where you are, but would be 
>> happy to
>>
>> > make other suggestions based on the coverage you seek.
>>
>> >
>>
>> >
>>
>> >
>>
>> > 73
>>
>> >
>>
>> > Lyn, W0LEN
>>
>> >
>>
>> >
>>
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>>
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>>
>
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