Monday, May 20, 2013

Titan Dx part 3 - the final part

he Titan is in the air.  My intent was to mount the antenna to a currently installed chimney mount.  Unfortunately, the chimney mount was in a state of disrepair from several years of weather exposure.  The antenna was placed on a 15 foot pole which placed the base of the antenna about 4 feet above the roof line.  A guy kit was secured from gap and a set of 3 guys were installed.  The wind survival of the antenna appears to be pretty good but time will tell.  The antenna is extremely top heavy so I would certainly recommend a guy kit for all but the most shielded of installations.

For my antenna, I did not utilize the 40/10 meter "hoop".  Instead, I fashioned 2 wires of length equal to what would have made up the 10 and 40 meter portions of the hoop.  The SWR on all bands but 30M is respectable.  I still have some experimentation to do to improve the 30M SWR.  I have not tried this antenna beyond SWR testing on 80 meters.  On 80 I have this antenna tuned for the extreme low end of the band  and I get good VSWR on the lower 50KHz of the band.  It was a bit lower than I wanted but I can live with it.

I spoke with the Gap folks this past weekend in Dayton.  They suggested that I increase the amount of overlap between the longest lower tuning rod and the rod that it is connected to.  This is supposedly the portion that resonates both the 20 and 30 meter sections.  I will see what I can do.  It is not a priority as this antenna is intended to be a multiplier antenna in an SO2R contest setup and 30 m is not going to be used.

First impressions of the antenna are positive.  I have made various contacts on 10 through 40 using the antenna both state side and DX.   How does it compare to a Steppir.....  not even in the same league!!!  Compared to my dipole, the antenna hears about as well for the most part.  I will continue to experiment and may report back in future blogs.

OK back to the modeling.  As I pointed out earlier, I spoke with the folks from Gap with respect to modeling as well.  They attempted to simulate the antenna with Eznec as well and were equally in successful.  It was explained that the close spaced rods just make this antenna impossible to simulate even with NEC4.  As it stands, I will end my attempts as it seems futile.  I will enjoy the antenna as it is.

Until next time,

Thursday, February 21, 2013

Titan DX part 2

I have been toiling over the models for the Titan for some time now.  I promised some results here but I am not willing to release what I have learned until I am sure of the accuracy.  Currently the models show some real promise but are not yet verified.  I am still unable to simulate the 80 meter operation of this antenna which disappoints me a great deal. 

The primary problem in modeling this antenna is the feed method.  The coaxial cable supplied by Gap runs the length of the antenna but the shield is split at the "gap" to provide the feed.  The 80 meter tuning capacitor is connected between the center conductor and shield at the very top of the antenna. The center conductor then ties to the very top of the antenna.  I have been using the capacitance of the coaxial cable in series with the feed point to complete the feed connection.  At this point, I see a number of VSWR nulls at approximately the correct frequencies (within 1 to 2 MHz) but no null for the 80 meter band.   I am still working on the models to improve the results. 

The 3D antenna patterns at the VSWR nulls are not bad at the higher frequencies.  The gains are roughly 2.6dBi for 10, 12,and 15 meters in the models current state.  The remaining bands display either 0 or negative gains at this point and that is the reason for the questioning the accuracy of the model. 

I will continue to explore and hopefully report results very soon.

Until next time

Thursday, January 17, 2013

Titan DX

So I purchased a used Gap Titan DX off of EBAY.  The previous owner was located about 2 hours south of me so I was able to pick the antenna up from his home and bring it back to my QTH.  The 80 Meter portion was tuned for 3.8MHz but a quick call to GAP Antennas put a new capacitor in the mail that should put me down closer to the 3.55MHz that I would like to center on for CW and RTTY.  Of course I have a 3 element STEPPIR on a 50 foot tower so this will be my second antenna setup.  My XYL is THRILLED!!!! ;-)  After I put up the elevated guy system, she said no more towers in the yard.  THIS IS NOT A TOWER!!! ;-)

The documentation with the antenna is fairly detailed with out a lot of drawings.  It seems fairly easy to put together but then again I am fortunate in the fact that this antenna has been put up before and has some of the more complex sections already put together. I suppose I may be singing a different tune once I actually put the pieces together.  I expect to get my exercise when it comes to tuning the antenna for 40 meters.  If you are not familiar with the Titan DX, the counterpoise loop tunes 40 meters.

I placed an order for  a guy kit from Gap Antenna, a coax ground assembly with bulkhead from DX Engineering and some LMR600UF (my go to station coax) and Polyphaser from Antenna Farm.  I plan on mounting the antenna on a chimney mount that is already in place.  The guy kit was purchased because GAP recommends not putting the antenna on a chimney mount with out one!!

The Titan DX is actually a vertical dipole and as such needs no radials to function.  I modeled the antenna in EZNEC and if the results were accurate,  the antenna is not exactly omni-directional on all bands.  Gain wise, the antenna is probably a pretty good performer on 20 and 40 meters but 10 and 15 meters may not be all that great.  On the air time will tell.  Again these results are based on an attempted tape measure derived duplication of the antenna in EZNEC.  I was unable to get the 80 meter cap incorporated into the model so that may also be skewing the results.  I will be enhancing the model as I learn more about EZNEC so I will probably write up some more quantitative results as I improve the model.

I am currently waiting on the delivery of the coax and a warm day to put this thing up so once again I am at the mercy of Illinois weather.

Thanks for reading my first post for 2013.  Comments are always welcome.

Until next time