Keep in mind that you should arrange some form of coupling as mentioned below and do NOT
connect scope probes directly to your feedline. Even 100 watts of RF at 28 mHz on a 50 ohm
line will produce a voltage that exceeds the ratings of the probes and will destroy them!
Yes, I know this from experience.
On 12/10/2012 10:21 AM, Paul wrote:
The easiest way to use an oscilloscope as a waveform monitor is to obtain and use a
Heathkit SB-610 waveform monitor.
SB-610 manuals have a decent tutorial on their use.
Another route would be to obtain an analog 100 MHz service oscilloscope, such as a
Tektronix 465, and connect the input of the 'scope to the center conductor of your
antenna feed line. Set the scope to trigger on AC, auto trigger and a 2ms (millisecond)
sweep rate. You will (should) see a trace. Adjust the vertical gain as desired while
transmitting a carrier into a dummy load.
Then when you talk into your microphone your voice peaks should just approach the 100%
carrier level. If your voice peaks exceed that level your amplifier will be flat
topping and splattering across the band. If the peaks are less than 100% you are not
using your amplifier to full capability.
When you get used to the AC and auto trigger you can experiment with internal triggering
to obtain a stable waveform on ssb and or cw.
One of my several pending projects is to modify an old 3" RCA oscilloscope for waveform
duty by installing a couple of SO-239 rf connectors, looping the center conductors
together, and running a lead from the center conductor wire through a decoupling
capacitor to one of the vertical deflection plates.
If you can find an oscilloscope that does not have triggered sweep you can obtain these
really, really cheap and the CRT (cathode ray tube) will probably have very little use
as these 'scopes did not work very well and had very little usefulness. First, make
sure it works, then install a couple of SO-239's for RF feedthrough, tap a bit of the RF
through a capacitor to one of the vertical deflection plates and you are in business for
signals below 30 MHz.
de Paul, W8AEF
-----Original Message----- From: Jukka Tarvainen
Sent: Saturday, December 08, 2012 12:54 PM
To: amps@contesting.com
Subject: Re: [Amps] Vacuum Relay
I use an oscilloscope waveform monitor and it was very obvious on the scope,
but for some reason not many hams use a scope as a waveform monitor.
Would be nice to have how to instructions for dummies on this subject.
73 de Jukka OH4MFA, OG4T
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Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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