2011-01-22 DIAMOND X30 2m 70cm 1m30 Colinear inside

Having relative poor signals on the local 70cm / 2m channels using this Diamond collinear 70/2 combi antenna at a height of 25m. I needed to investigate what could be wrong.
Measuring the cable only 3W is left for the antenna of the 10W 435MHz output from a IC451E
The cable is 30m type H100 Z50 10mm outside diameter it is semi air-spaced but has an impossible 4mm² solid CU inner conductor not much air left. I preferred the H43 Z75 cable having lower loss and mechanical better ratio in conductor size but it is no longer selling i think. This H43
3W should be enough for a comfortable noise free FM signal. But only 27km away at PA0A the signal is weak too weak something must be wrong? I made a simple reference dipole of 2x17cm CU wire.
With this dipole the signals where totally worse. So the Diamond does work?
I got curious to look inside. Maybe moisture penetration degraded the antenna.
This  antenna is rainwater close in its normal vertical mounting position. But take care if your mast can be tilted downwards then rainwater will flow in immediate the connector base is not sealed.

Inside the fiber tube there is a long copper wire with two coils.
One at the base (picture) with 2 C's and another  40cm off the top with no extra C's 
The joint of the 2 C's is the inner pin of the SO239 connector.
The Air-coil underside is soldered to the connector house.
The antenna is connected to the Tap on this coil through a C ( 8.5pF)   I think the base coil  and its 2 capacitors function as matching network.

Seems a rather small value to me this 8.5pF for 144Mhz.
The other C is parallel over the connector i do not know that C value.The 2nd coil must be the usual Collinear section divider for 70cm.

Then in the middle there is an brass tube of about 40cm where the inner conductor goes through  but i measured no galvanic connection. I thought maybe that's the problem...  Had to force it open to see but there was nothing inside! Just an isolated section? 

  Halve way the wire lead through a 40cm x 10mm diam. brass tube. Both ends are fixed in an 25mm long isolator bus. How does this work? As coupling capacitor then its a very small one of about 2pF per side.  

The mysterious tube in the middle

Still not solved the problem the antenna seems to work at least better then a simple vertical dipole. The cable is not super the insertion loss should be about 2.5dB now it is over 3dB
Also i have the Diamond MX7 2 N Duplexer inserted that gives another 1-2 dB loss at 70cm  But those losses can not explain the weak signal i have at this height  and distance?



PE4BAS, Bas said…
Hallo Jaap, inderdaad een beetje apart probleem. Die H100 kabel heb ik ook gehad. Gebruik sinds jaren Aircom+. Had met de H100 ook veel verlies. Denk dus toch dat het aan de kabel ligt. Mijn X30 heb ik vorig jaar verkocht, vond het geen geweldige antenne. De W2000 diamond kloon doet het op lagere hoogte een stuk beter op 2m/70cm. Voordeel is dat daar ook nog 6m op zit. 3 vliegen in 1 klap :-) 73, Bas
Artur Kulichev said…
This my X-50: http://fotki.yandex.ru/users/arturku/album/214067/
Messere said…
Dear PA0O,
a lightning has burned my antenna X30 and I'm looking for the capacity of the two capacitors.
The first one is a 8.5 pF (500 V ?)
Do you know the capacity of the second one?
Thanks a lot
Antonio IW0GPW
Jaap van oosten said…
hi Messere
Sorry for late responce
I could not read the value of the parallel C
my guess it has the same 8.5pF value

If I bring the antenna down again I can unsolder that C and measure it's value

I have had the mast down
measuring only 2.5W left of 10W at 430MHz
H100 33M it is rated 8.8dB 435MHz 100m it should be -3DB # 5W left
the cable may be damaged
Jaap van oosten said…
this parallel C might be 2.5pF
refered to site of PA0FRI
they can be replaced by short pieces of coax to make it more weather/ power proof