Tennadyne T11

[W4DEE]

How is the best way to check SWR on a t11 before you put it on the tower ?

[W5WSS]

Since the Earth surface effects the feedpoint impedance of antennas any measurements taken when the horizontal beam is close to and parallel are not regarded as very accurate.

Some want to double check anyway and place the reflector pointing towards surface and director toward sky.

Their logic is that this helps DE couple the entire antenna system for a more accurate measurement.

One must install the antenna and one is going to measure perhaps in the end one is going to proceed with final tuning after the antenna is up in the final position anyway.....I make no presumptions.

 

[WB2WIK]

Since the Earth surface effects the feedpoint impedance of antennas any measurements taken when the horizontal beam is close to and parallel are not regarded as very accurate.

Some want to double check anyway and place the reflector pointing towards surface and director toward sky.

Their logic is that this helps DE couple the entire antenna system for a more accurate measurement.

One must install the antenna and one is going to measure perhaps in the end one is going to proceed with final tuning after the antenna is up in the final position anyway.....I make no presumptions.

 

Except the T11 doesn't have a reflector.  It's a log periodic and all elements are driven.

I've found with these (I have two Tennadyne LPDAs) since the elements are not adjustable at all, there's really nothing to adjust.  I just put them up on the tower and they work fine; never had a problem.

I have seen people have problems with them, though -- because they assembled them wrong!

[WB6BYU]

But perhaps the reason to check the SWR is to make sure you didn't make any
assembly errors!

One approach I've used with yagis is to point them straight up in the air with the
rear element a few feet off the ground.  It's not perfect, but it might be good enough
to catch construction errors.  It isn't always convenient to do this, particularly with
larger antennas, but you might be able to hoist the front of the boom up the tower
far enough.

[W5WSS]

Yeah true they are not regarded as a reflector but rather a rearward set of transposed halves split and insulated from the support structure.

I know because I designed and built my own as far back as the early eighties

But oh by the way one could include a parasitic reflector within a log periodic design.

Anyway as I said try it and see.

[W8JI]

I don't know about the current manual, but the old manual guaranteed wrong assembly. It told people to tape the coax along a boom.

Since each boom is one conductor of a two conductor balanced transmission line, this is exactly like telling people to tape coax to one wire of an open wire line.

http://www.w8ji.com/baluns_on_log_perodic_antennas.htm

Before I installed a log, I'd make sure the feedline was routed correctly.

73 Tom

[WB2WIK]

I don't know about the current manual, but the old manual guaranteed wrong assembly. It told people to tape the coax along a boom.

Since each boom is one conductor of a two conductor balanced transmission line, this is exactly like telling people to tape coax to one wire of an open wire line.

http://www.w8ji.com/baluns_on_log_perodic_antennas.htm

Before I installed a log, I'd make sure the feedline was routed correctly.

73 Tom

The old manuals had another problem (I don't have a new manual so not sure what may have been corrected): No clear photos of the entire assembly.

I've seen people assemble them thinking everything was perfect, but they ended up placing all the left side elements on one boom and all the right side elements on the other boom, which obviously doesn't work.

But the instructions, which warned about this, never clearly showed exactly what it should look like when properly assembled.

[W5WSS]

My design utilized Phenolic flat stock so the transposed feeder system, the periodic cell of aluminium tube elements were all isolated from the aluminum boom because the entire cell was RF and DC insulated via the Phenolic plates.
This allowed the boom to be dc grounded without disturbing the cell function or choke technique at the feed point.
This technique addresses the tennadyne vulnerability before tennadyne ever designed one.

The boom a 2" dia tube was a mounting structure to correctly install each of the plate to element brackets and facilitate the proper alignment.

The apex pair of cell elements were split and fed.

The boom cold to the feed line.

I do not like using the boom double duty as strips serving as the transposed feeder system for 180 degree phase shifting

Although I do endorse wide diameter strips from butt end of each element to next crossover point.for that function.dedicated to the ends of each for the purpose of transposed feeder methodology rather than wire.

 Incidentally the antenna was fabricated as designed and intended to work and understood to not need a tuning mechanism.and it did not need one upon the top final position.

I installed it and was matched properly in the first place because I designed it that way.

I did feel compelled to take a peek at the swr prior to the installation and did point the apex toward the zenith and nothing remarkable was noted.

I like my design that avoided those suggestion of precaution in the first place....