[Elecraft] 6 meter beam - OT

[Lew Phelps K6LMP]

OK, point well taken. I was comparing dBi (isotropic antenna) to dBd (dipole), and that is not appropriate. However, the gain figures I quoted are free space calculations.  

To correct the comparison, the free space difference is 2.15 dB 

(reference: http://www.digi.com/support/kbase/kbaseresultdetl.jsp?id=2146)

thus, the 8-foot boom Yagis in the table would equate to about 7.65 to 8.65 dBi gain, which is still a 1 to 2 dB less than the free space gain of the described quad, on an apples to apples comparison. 

sorry for not getting the comparison right the first time. the differential between Yagis and quads is less than I originally stated, but still non-trivial.

Of course, if you're building arrays for EME work, the Yagi is much more practical. For a single antenna, I still think the quad is preferable.

Lew K6LMP 


On Mar 18, 2010, at 11:30 AM, Lance Collister, W7GJ wrote:

> Hello Gary,
> 
> Just be careful comparing information you receive from different sources!  That is 
> why we put together the VE7BQH comparison table, with all antennas listed in FREE 
> SPACE GAIN COMPARED TO A DIPOLE (DBD).  Gain figures look unbelievably good when an 
> antenna gain in dBi is compared to a conservative dBD value.  Many antenna 
> performance calculating programs also include up to 6 dB of extra gain for the peak 
> GROUND GAIN LOBE when the antenna is aimed on the horizon over flat perfectly 
> conducting ground.  Be sure you compare apples to apples or you will be very 
> disappointed in whatever antenna you build.  Good luck and VY 73, Lance
> 
> On 3/18/2010 5:03 PM, Lew Phelps K6LMP wrote:
>> 
>> For a Yagi to achieve gain similar to a three-element quad, you need to double the
>> boom length.  If you look at the marvelous spreadsheet that VE7BQH posted a bit
>> earlier, you'll see that single Yagis of about the same boom length as the
>> three-element quad offer free space gain of only about 5.5 to 6.5 dB, and Yagis
>> with about 9.5dB have boom lengths of roughly 1.1 wavelengths, more thn twice as
>> long as needed for a comparable gain quad.
> 
> -- 
> Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8, E51SIX)
> P.O. Box 73
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> TEL: (406) 626-5728
> URL: http://www.bigskyspaces.com/w7gj
> 2m DXCC #11/6m DXCC #815
> 
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