[TowerTalk] 10 throu 20 beam traps or no traps

David Gilbert xdavid at cis-broadband.com
Sat Jun 21 22:35:57 EDT 2014

Except that as far as I know Mosley never did adjust their inflated claims.

On the other hand, as an owner of two Optibeam antennas (OB2-40 and 
OB16-3), I have considerable confidence that the claimed specs are 
reasonably accurate.   I loaded EZNEC+ with the physical measurements 
shown in the manuals and came up with virtually the same pattern and 
gain as claimed by Optibeam.  I also, with the help of K9RX who lived 
about thirty miles line of sight from me at the time (we both lived on 
high ground with a lower elevation between us), measured the actual 
pattern of both antennas and again corroborated the claimed figures.  
Nobody on this earth will ever convince me that the Mosley three element 
trapped yagi has equal or better gain than my OB16-3 with it's four 
full-sized elements like the published data suggests.

Dave   AB7E

On 6/21/2014 6:07 PM, Jim Brown wrote:
> On 6/21/2014 3:23 PM, Dan Hearn wrote:
>> It is interesting to note that the Mosley claimed gain is about 2db
>> greater than other tri band beams. They use dbd reference instead of dbi
>> while I think their claims would be about right if they used dbi 
>> reference.
> Exactly the opposite. The peak gain of a dipole is 2.2 dBi. So a gain 
> specification of 4 dBd is equivalent to 6.2 dBi.
>> I suspect if you used a good line choke at the coax feed point and 
>> subtract
>> 2.1db from their claimed gain you would have a typical triband beam.
> I don't agree with that logic or that statement. A simple common mode 
> choke simply reduces common mode current, which mostly prevents RF 
> received on the feedline from filling in the nulls in the pattern.
> In his book, "Array of Light," N6BT shows optimized designs of 
> 2-element, 3-element, and 4-element MONOBAND Yagis. He put these IDEAL 
> gain figures in a table with the CLAIMED gains of a dozen or so 
> competing products. In nearly all cases, the advertised gains were 2-3 
> dB better than the best monoband beam. In other words, they claimed 
> impossible gains. After the first edition of "Array of Light" was 
> published, nearly all of those manufacturers revised their gain 
> claimed downward by several dB.
> 73, Jim K9YC
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