[TowerTalk] More on Array's from N0AH

[Dinsterdog@aol.com]

This is in response to the many array comments I have received since posting 
my K8UR experience a couple of days ago- so far, I've gotten about 20- Dick 
Green, WC1M, had a great follow up article with many good points as did Pete, 
N4ZR, and others, that I want to comment upon-

Dick, 

Check out CQ Contest Magazine Sept 2000...my write up on my 80 meter 1/4 wave 
vertical sounds just like what you went through building your 40 meter 
vertical array-  

Amazing coincidences between what we both went through to build a 1/4 
vertical array-  just remember everybody- the K8UR 1/2 wave dipole design is 
a great way to go unless you have a few months to build a radial system for 
the 1/4 wave vertical option- hihi 

The power dump at higher frequency was in my post, I thought- ...I sent it to 
someone.......hihi-  It turned out flat, probably around 1%,  for about 30KHz 
centered at 7.050MHz....it curved upwards to 5% at 7.150MHz and 10% as I got 
close to 7.225MHz- so it's a pretty sharp increase-  but if I centered the 
array around 7.100MHz, I think I'd be dumping around 5%-8%  on the band edges 
of 40 meters that I consider to be 7.000MHz-7.225MHz-, maybe 15% as I got up 
towards 7.300MHz, but who goes there- yuck..............hi 

But I'm like you- most the action on 40 meters is the CW window and that's 
where I have tuned my K8UR array- I really thought my meter was busted when I 
transmitted in the 7.050 MHz range and it didn't move- and the meter was set 
on a 20 watt scale running 100 watts out of the rig- 

I'm going to run legal limit through the array in the next couple of weeks 
(Need to get a 500 foot feedline from the antenna tower to the shack) and 
then check the meter- it will give me a bit better of a picture of what's up- 
 but I doubt if I will have any surprises- 
 
I've tried to get the 80 meter array power dump flat but it just won't happen 
unless I go with full size radiators I'm afraid-  

I agree with you that a power meter should be maintained in the shack from 
the hybrid coupler power dump port to a dummy load sitting under your desk.  
I've had fluctuations in the array's performance that the meter will pick up 
on-especially when the meter goes dead but the antenna is still seems to be 
working.  

This happens, for example,  if your coax connections between the dummy port 
and the dummy load come loose-the 50 ohm dummy load must be hooked up for the 
array to work!!  And if you have a 50 ohm load sitting outside at the tower 
and something goes wrong- you may not notice it right away and end up smoking 
the rig with a high SWR feeding back into the rig.

 Especially if you are on the edges of the array's resonant points- Even if 
you are centered, your F/B will go south on you if the dummy load gets 
unhooked by accident-

Make sure you use a 1.5KW dummy load...in last year's CQWWCW contest, I ran 
my array with legal power dumping about 20% of power into the dummy load. At 
the time, my array was centered around 3.800MHz- You could cook an egg on the 
dummy load- but at least I had my meter showing the array was doing what it 
was supposed to do- and I was able to operate out of the systems resonant 
point without blowing up my rig-

But if the dummy load became unhooked, my rig would have fried with the SWR 
that the hybrid coupler was hiding and dumping off-  so the power meter to 
monitor the dummy load input is critical-

That's the amazing thing about using a Collins feed system device, such as a 
Comtek Hybrid unit,  I swear that you can operate way out of resonance, to a 
point,  and the darn thing still works thanks to unused power going into a 
dummy load- -

So what if you are only getting 80% of your power out, and your F/B goes from 
20-25dbs down to 10-15dbs-  still one heck of signal compared to a single 
element vertical and/or dipole- And you can play on the edges of a big band 
like 80 meters with a Collins fed array vs. having to cut off at a certain 
SWR reading with other systems-  

I'm not suggesting it, I'm just saying it's possible,  to a reasonable point, 
 to work the entire band with a Collins fed system even if your outside 
acceptable resonant point range as measured by SWR on other systems-- 

But coming full circle, this is why it is so important to array builders 
using Collins systems, like the Comtek System hybrid coupler, to get to that 
lowest power dump reading as you can go-  

Don't just settle for a 10% reading thinking you won't ever need much 
bandwidth cause you only want to operate 15KHz of a band-  like I did when I 
first put up my 80 meter array for the DX SSB window- Just cutting down from 
10% to 5% will give you as much as 200KHz more bandwidth to operate with a 
reasonable power dump into the load-  by reasonable, I mean no more than 20% 
of your output power going into the dummy load-

I can't tell you how relieved I was to center my 80 meter array from 3.800MHz 
to 3.650MHz when I figured out how to lower my minimum power dump from 7% 
down to 3% by simply increasing the top loaded verticals by 8 feet and 
shortening the tophat wires- 

 I'm still using top loaded verticals but now I can cover the entire DX 
portion of 80 meters from 3.500MHz to 3.800MHz and only dump around 5-10% of 
my power on the edges.  Before lowering my minimum power dump reading, I was 
running around 7-10% in the ssb window and 20-25% in the CW window- 

I did hear from a few ops who had parasitic arrays using voltage fed systems 
and they only get 10-12 db F/B-, tops- Pete, N4ZR I think stated he was 
getting around 4 db F/B...... so if you are going to put up an array, you 
might want to sit down and go with a current fed system- you will improve 
your chances for a better F/B and perhaps get up to  20-25 F/B..........it 
might cost a bit more as system to do it, but man- what's a dB worth eh? 

Pete, N4ZR, posted some great notes on his parasitic array on Tower Talk 
recently-He mentioned the possible disadvantages of having to dump power 
using a Collins system vs his parasitic array set up-  a good point, 
but............

What's the difference of dumping power into a dummy load due to resonant 
points vs having it reflected back into the rig as measured with higher SWR 
with other types of systems??  

Using either a parasitic array or Collins fed system, isn't unused power,  
unused power,  be it seen in a higher SWR coming back into the rig or as 
unused power burning off in a dummy load as with a Collins feed system??  I 
honestly don't know whats better but I'd rather have unused power going into 
a dummy load vs my rig- 

Like Pete said about his 80meter parasitic array, my F/B also seems to vary 
very little on my 80 meter vertical array going from 3.500 MHz up to 4.000 
MHz ........but without another array tuned at the top end of the band for 
comparison, it is tough to see the what is the true deteriorated F/B of 
listening outside the array's specific band edges can be to the 
ear...........I still get a decent F/B listening to SW with the 80 meter 
array- not great, but noticeable- 

I did consider making my 40 meter array a parasitic system........What you 
do, is incorporate the feedlines to make the unused dipoles appear to be 
longer vs the dipole that is in use-  each dipole must have a separate ground 
for the system to work- and you need an antenna switch box using DPDT relays 
so as to keep the grounds isolated on the dipoles you are not using-..by the 
time I figured out how much this would cost to home brew-  I decided to just 
keep with Comtek Systems-  They have great instructions and a device that 
works out of the box- take that MFJ! 

(Parasitic arrays are for the die hard home brewers as I don't know of a DPDT 
antenna relay box out there-!!!)   

Pete made reference to the variations in F/B with his parasitic array-  I get 
those too- 

There is a big difference at times, with a lot of inconsistencies,  on F/B 
with closer range stateside contacts vs. further away DX contacts, say over a 
1,000 miles, where 20-25 dB F/B readings seem to be much more consistent--

As far as ground wave signals are concerned- you may not notice any F/B at 
all under certain band conditions- - 

K0RF and I tested each of our 4 SQR dipole arrays out at a distance of around 
100 miles and I think we thought we had broke something- hardly any 
noticeable F/B gain at all-  but this was about an hour after sunset and I 
think we both agreed that during the day-, or under different band 
conditions,  we would see a lot more-  Interesting thing here is that I had 
just worked a W-6 in his daylight on the left coast and I was seeing 20-25db 
F/B and was giving me reports that varied by 5 S-units between the antenna I 
had on him vs beaming the other direction-cool stuff!

Steve, K8LX, referenced the need for radials on 1/2 wave systems.....I know 
that Jim at Comtek Systems is doing test on incorporating radials now on the 
K8UR 1/2 wave dipole array this summer-  I'm sure his results will be of 
great interest to everyone interested in this subject-  I agree with many on 
the reflector who have suggested a decent ground screen below the dipole 
array and/or radials, even if only a few, attached to each leg of the tower-  
It can't hurt and most likely it has to help- but by how much is the question-

I think the future for array's is pretty bright-  I'm not sure why they are 
not more widely used- but it is great to see all the attention they are 
getting these days- And I wonder if there are many ops using array's on the 
higher bands?  

I had a Super Scanner as a kid back in the 1970's- it was a three element 11 
meter vertical array that you could switch around the 3 directions that the 
elements were at using a switch box on the shack desk- or the box would allow 
you to have all three elements active at once- - it was fun and worked great! 

It wasn't huge- but I do remember it using 1/2 wave vertical elements- and 
the booms were about 2-3 feet long-   I still see them on a few truck stop 
buildings out west here-mostly broken and bent-  but it's been about 20 years 
since they were made- but I wonder what it would be like to see them made for 
10 and/or 15 meters??? 

You never know-  Maybe we are on the edge of an array revolution- 73  Paul  
N0AH

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