[TowerTalk] Directivity and F/B Ratio was Re: FW: Force 12 Delta 240 2 Elem 40M Yagi

[Pete Smith N4ZR]

Just one small addendum. If you set the electrical length of the 
reflector at, say, 7200 KHz, you may well find that the antenna reverses 
direction down at the low end of the band, presumably because the 
reflector is so much too short that it becomes a director at that 
frequency.  I found this experimentally by using a remote signal source 
(an MFJ259B) a few hundred feet away to determine the point of maximum 
F/B, and then moving it to 7050 where it would not reverse until well 
below the band.  N6BT points out in Array of Light that the resonant 
frequency of the driven element is only important for matching and 
losses, not for gain or F/B.

73, Pete N4ZR
Check out the Reverse Beacon Network at
http://reversebeacon.net,
blog at reversebeacon.blogspot.com.
For spots, please go to your favorite
ARC V6 or VE7CC DX cluster node.

On 4/15/2014 2:23 AM, Matt wrote:
> I will echo that the comments by all are valid.
>
> I have the EF240X & an S402.  Both are 2/3rds wavelength (~45') elements on
> 24' booms.  The EF240X is linear loaded and the S402 is base loaded.   Both
> give an SWR bandwidth of about 250 khz and both perform about equally.   Be
> aware that the F/B bandwidth on both antennas is much less than the SWR
> bandwidth and deteriorates quickly down to only about 5db as you get out
> towards the band edges.  This does not present any issue as a transmitting
> antenna but receive performance suffers noticeably because poor F/B often
> means lower S/N ratio - especially when your wave angle is not optimum.   It
> does not really matter if you plan to use Beverages for receive.   As
> transmitting antennas go, gain peaks at a little over 4dbd and decreases
> down to about 3db or less at the band edge.   So on both transmit and
> receive both of these antennas are noticeably better than a dipole
> (theoretically and observed in use).   Mechanically, the S402 is built much
> more stout then the EF240x, but it is also twice as heavy with almost twice
> the wind load area.
>
> I am currently converting the EF240X into a 3 el beam for 30m with full size
> elements by replacing (and extending) the insulator at the linear load joint
> with tubing.   The loading wires will be replaced with non-conducting
> supports.   The driven element will be the new element and be
> self-supporting.
>
> I am planning to convert the S402 to a 40m Moxon in hopes of realizing full
> SWR bandwidth and broader performance bandwidth.  The models look promising.
> I still have some work to do on the mechanical details but the element
> stress analysis looks good so I think it is "do-able".
>
> Hope this information offers some insight into the nature of the trade-offs
> with the shortened 40m beams.
>
> 73
> Matt
> KM5VI
>
>
>
>
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of
> Edward Sawyer
> Sent: Sunday, April 13, 2014 6:07 AM
> To: towertalk at contesting.com
> Subject: Re: [TowerTalk] Force 12 Delta 240 2 Elem 40M Yagi
>
> I owned and used the EF240X from Force 12 for about 7 years.  The antenna
> actually worked very well once tuned but it had 2 issues.  It was very
> sensitive to its environment on tuning so you could not set it to the
> factory and put it up.  You had to raise it up to 40 ft or so and then bring
> it back down.  The second issue was that the rigid aluminum wire of the
> loading/boom support structure was not robust and I had to repair it twice
> in the 7 years.  The good news, and why I bought it, was that the bandwidth
> on the 240X was 250khz (and it was).  Overall, I liked the antenna despite
> its quirks.  Oh yes it was very light as well.
>
>   
>
> I now use a M2 3el on a 32 ft boom.  That is a killer antenna.  Its got a
> 200 - 220 khz BW and more gain.  More robust.  But its heavy at over 150lbs.
> The cost of it is not much more than the 2 els from F12 and CC but it will
> blow the doors off either antenna.  I have held a run frequency on CQ WW,
> ARRL DX, and WPX on 40 SSB using 100W and this antenna at 85 ft.
>
>   
>
> 73
>
>   
>
> Ed  N1UR
>
>   
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>