Topband: Spitfire question

Tue Nov 12 16:28:33 EST 2013

GE Eddie, Felipe, some direct mailers and all,

seems, the spitfire array got some interests, I got also some direct mailed questions.
I will try to answer, and try to remember my tuning way 2003 - 2006.
Just found some, maybe 20, Din A4 handscribed papers, from tuning procedure 2006;
but need to remember some details not wrote down :-)

Also I need to update my homepage; newest HAM-radio details are 6 years old, there 
changed a lot. 

At first, description of my array and anything around:
- center tower is 27m high, grounded. Fired by gamma-match for 80 and 160m. Caps are 
now Variabel VACs for GU84 power (homepage not updated)
- Radials: Using ~120 radials, between 10m and 30m long. Additional buried 4 x (10mx0.6m) 
chickenwire. During Winter 4 to 6 times chickenwire 10m to 25m long. Around centre tower
16m² chicken wire
- Unused elements of the array are grounded via 3mm Cu and the radial net.
- Array Wires had been ( shortly destroyed by a storm :-(  ) 1mm copper with steel inside.
- QTH is relativly flat and empty, only to SW over W to NW there are less buildings. Trees 
and bushes are not very high or far away the other directions. 
http://www.df9ox.com/e_afu_rxants_bev.html
- ground seems to be very conductive, QTH here near a main german river, Elbe (4km). 
Groundwater in summer 1,4m, winter 0,7m deep. For my beverages transfering -12V via 
ground is no problem.

My array seems to be working ok (80m)
I can see up to 25dB f/b, up to 35db f/s.
Gain is up to <6dB.
But often it is also much lower, depending on elevation angles and conditions.
All compared to the single center tower.
When using the single center, everything else is grounded.

Reference *1: I will use some abbreviations (W1,W2,W3) down, this is the file:

http://www.df9ox.com/docs/Spitfire%20Dimensions%20(other%20bands).JPG

Reference *2 for the array description is:

http://www.df9ox.com/docs/FVR%20Spitfire.ppt

@PY1NB 

No, I do not have any files for NEC.
Maybe John W1FV or Fred K1VR as the authors can help out.
All I find around 2007 in internet I mirrored on my homepage.
ON4UN described the spitfire in chapter 3.7.4, I think he modelled it with NEC. 

@LU2DKT

Hello Eddie

I did it the same way, tuned it for maximum f/b, but used no caps at the corners, changed the 
length.
Especially changed W3 (reflector only), w1 and w2 (director and reflector).
I followed *2, page 8 and 9. Thatswhy I gone only for f/b, because gain should be ok in that 
small QRG area, while gain area is much broader.

Starting point was good f/b on 3650kHz with the aim of 3510kHz.
So I need to make something longer.

> 1 - Did you just adjust both elements in one direction for max f/b ?
> or gain ?

1. Started with the reflector part, W3, later I made some tests with the director part W1-W2.
Always changed all 4 directions in the same way, but tried to find some differences between  
the 4 directions in the evening. But this did not happen here, changes were equal.
Was looking for good f/b.

> 2 - Did you start with the dimensions given by the authors and then
> change it a 
> little bit at a time ? both of them or just one of them and then the
> other? in which 
> direction adding or shortening

2. Yes, started with the given dimensions.
Changed it typically in 0.1m steps; if I saw a result like "0.1m makes 15kHz", changes like 
0.2m or more were done.
At first only reflector part, W1, later I made some tests with the director part W1-W2.
If I saw I was above 3510kHz with best f/b, increasing; otherwise decreasing.

> 3 - Do you have notes about how much your element length differ from
> the 
> original design? could you share those numbers?

3. Yes, I ended with W1-W2, director, 0.3m longer (W1 26.9m => 27.2m),
reflector part W3 1.1m longer (W3 3.5m =>4.6m). 

> 4 - Did you measure element resonance after you antenna was working?
> how 
> did you measure? (in order to repeat it in here)

4. Yes, I did a lot measurement with my MFJ 259 at the corners (W1 W2), also after finished 
tuning.
But I am not sure with my handscribed papers at this point with exact F-resonance
versus dimension of W1, W2 and W3. 

> 5 - Finally, how do you achieve omnidirectional radiation? did you
> just open at 
> the corners or ground each element?

5. Grounding all elements

> 6 - If you ground it, how do you do that? a ground pipe o connect it
> to the vertical 
> radial system?

6. Unused elements are grounded via 3mm Cu down the post and connected to the radial 
net.

Eddie, don´t know whether that will help you.
For my understand of the array you still found that best gain point if you are in the maximum 
peak of f/b.

You measured 1dB gain at 0° elevation angle, thats ok, maximum gain is >20° elevation.
You did yet not seen any noticeable effects on signals from EU and PY.
Maybe because of still no flat angle conditions?

I see many times also less gain, but f/b is good.
Other days there is really good gain, and less f/b.
And another day there is less f/b and no gain.
Depends all on conditions, incoming angles.

I would like to see there is a point which gives you an idea for improving something.

vy 73 de  André  DF9OX

> 
> Hello André, I really appreciate you took the time for sharing your
> experience.
> 
> I used for tuning the last procedure indicated by the authors, which
> was to use a 
> reference signal from the back (700 mts in my case) vertical
> polarized and adjust 
> both reflector and director back and forth for maximum f/b (using
> variable 
> capacitors inserted at the corners) which should give you also max
> gain across 
> the range.
> 
> Well....... f/b was good, more than 20db across 25Kc but I only got
> 1db gain 
> maximum.
> 
> I understand you did it using a practical way but, I still don´t
> understand how you 
> did it, because changing dimensions every day and waiting for
> results could give 
> millions o possible changes and difficult to decide which direction
> to follow.....add 
> or cut the reflector? add or cut the director at the same time .
> 
> Could you please be more specific ? or as specific as you can so I
> can repeat 
> your procedure?
> 
> 1 - Did you just adjust both elements in one direction for max f/b ?
> or gain ?
> 
> 2 - Did you start with the dimensions given by the authors and then
> change it a 
> little bit at a time ? both of them or just one of them and then the
> other? in which 
> direction adding or shortening
> 
> 3 - Do you have notes about how much your element length differ from
> the 
> original design? could you share those numbers?
> 
> 4 - Did you measure element resonance after you antenna was working?
> how 
> did you measure? (in order to repeat it in here)
> 
> 5 - Finally, how do you achieve omnidirectional radiation? did you
> just open at 
> the corners or ground each element?
> 
> 6 - If you ground it, how do you do that? a ground pipe o connect it
> to the vertical 
> radial system?
> 
> In my case I am using almost 120 radials 1/4 wave long for the 1/4
> wave vertical.
> 
> I definetly need a help to make it work. I am only interested in
> gain because I 
> have other receiving antennas.
> 
> Many thanks in advance for your time, 
> 
> Eddie, LU2DKT
> 
> --------------------------------------------------------------------
> -----------------------------------