Hi Dick, you have a big problem somewhere there I can get 200mA of antenna
current with 2 watts RF . If you your TX is 80% efficient and generating abt
80w and your total resistance is measured as 60 ohms you should get 1.2 amps
or close to that . 6.8 mH is way to low for that capacity which suggests you
have a funny on the tuning maybe and interaction with the transformer. You
could try tuning the antenna alone (no matching transformers) with the
bridge, and see it it tunes in the same place.
Cheers de Alan G3NYK
----- Original Message -----
From: Dick
To: [email protected]
Sent: Saturday, August 12, 2006 4:33 PM
Subject: PA4VHF small backyard tests
Well, changed the antenna and fired up my little teststation this afternoon
in my backyard.
Antenna: 3 wires 7.5m long spaced 40cm each , vertical part about 6m long
also 3 parallel wires spaced 40cm each.
Feed is about 2m from the far end.
Measured about 170pF and 60 Ohm (?) with bridge, noisesource/136kHz
oscillator and RX.
With variometer and loading coil connected, I needed about 6,7mH to tune
things, where I expected to find
around 8,0mH.
Somewhere I got around 30-40pF extra. Maybe internal capacity of the loading
coils???
With 100Watt DC-input I got about 200mA antenna current sofar.
Remarkable: when switching TX on/off, I could hear the first step-up
transformer clicking (it's a 58mm 3C85 core)
is this usual???
The transmitter used is my little testbox with an additional amplifier with
IRFP360 running at around 12-14V, 6-9Amp.
Mal has heard me before with this transmitter connected to a 15m spiral
toploaded vertical..........
73
Dick, PA4VHF (JO32eg)
|
