Topband: Flag problem solved

[Luis Mansutti IV3PRK]

Good afternoon friends,

following the comments and suggestions I got on the negative performance of 
my rotable Flag, I checked everything and discovered that the big noise was 
introduced by the preamplifier, which has been working very well for years 
with any kind of antenna.

Gary, KD9SV, wrote me:
-----------------------------------
Since building the unit you have I have started putting a 24pf capacitor 
across the 100k resistor to prevent the pre-amp from oscillating when source 
and load
impedances are not close to 50 ohms.  What kind of matching transformer are 
you using on the Flag antenna?
------------------------------------
The matching transformer is a 18:1 binocular BN73-202 (3 and 12 turns).
The impedances seen by the premplifier are:
- Flag    R 57 +jX 0 = SWR: 1.15
- Pennant    R 43 -jX 5 = SWR: 1.22
- Pennant with outdoor preampl. R 60 -jX 78 = SWR: 3.9
- 4 square mini-array  R 70 -jX 6 = SWR: 1.45

Despite the best matching, ONLY with the Flag the preamplifier was 
oscillating!
I substituted it with a spare ICE mod.123B and....beatiful, no noise with 
it.

But I could not survive without the KD9SV Dxpedition model as it containes 
also the indispensable Front End Saver ( see 
http://johnjeanantiqueradio.com/gary.htm or 
http://www.radiobooks.com/products/svdx.htm ) so I took the courage to put 
the iron gun inside it and add that small capacitor as suggested by Gary. 
Really an easy task even for a non technician like me, and ...WHOW 
everything was OK!

Now the Flag is quiet as the Pennants, with the output level abt one s-unit 
higher and the expected F/B from 20 to 30dB.
Its building is more demanding than the Pennant but, beeing rotable, has the 
great advantage to cover all the directions.

And now I'm going ahead with the K9AY loop building and tests......

Many thanks to all who wrote me directly with comments and CU on the Band!

Best 73

Luis IV3PRK