[Lowfer] A couple of crude Antenna Matching techniques - will either one work

[Zack Widup]

Does anyone here use a vertical antenna with a top hat for
transmitting? At least on 630 meters? The local road conditions
station in this area provided by the county transmits on 540 kHz and
uses such an antenna.

73, Zack W9SZ


On Fri, Dec 1, 2017 at 10:06 AM, Douglas Williams
<williamsdoug1966 at gmail.com> wrote:
> I wonder how close attaching an NE-2 to the hot end of the coil and tuning
> for maximum brightness would get you?
>
> On Fri, Dec 1, 2017 at 10:54 AM, Brian, WA1ZMS <wa1zms at att.net> wrote:
>
>> My 2 cents on this.....
>>
>> 1) Andy may be suprised how well his HF SWR bridge will work on 630m. The
>> Pout readings may be off, but the null for lowest SWR will be there even if
>> incorrect in magnitude.
>>
>> 2) Tuning under TX power could be an issue for some TXs based on the class
>> of operation the PA uses: Class A, B, C, D, E. Switch modes amps can act
>> strange under active load pull. Any amp can too though.
>>
>> 3) An ideal meathod for live tuning under TX power (for me) has been to
>> place a 6 to 10dB power attenuator in the PA output path. The PA will run
>> with a "reasonsble" load while you go outside and tune away for max antenna
>> current. The RF power and current at the antenna will be much lower, but
>> also less chance of getting RF burns as you tune and poke around. An
>> attenuator might be cheaper (homebrew) than an antenna analyzer.
>>
>> 4) I've done all the above for 2200m & 630m myself.
>>
>> -Brian, WA1ZMS
>>
>> > On Dec 1, 2017, at 10:14 AM, John Bruce McCreath <weazle at hurontel.on.ca>
>> wrote:
>> >
>> >
>> >
>> > Hi Andy….can you clarify a few things for me.  Is the bottom end of your
>> coil grounded, is the capacitor
>> > in parallel with the coil, are you tapping the feed line inner conductor
>> near the bottom end of the loading
>> > coil, and is its shield connected to the bottom of the coil/cap?  If
>> that’s the case, you should be able to
>> > bring it all to resonance with the meters you have.  I wouldn’t put an
>> RF ammeter at the top end of the
>> > loading coil, as it could really throw things off because of the high
>> voltage there.  The antenna current
>> > should be the same, regardless of whether it’s measured at the “cold” or
>> “hot” ends of the coil.  Do you
>> > have a means of measuring the transmitter final current?
>> >
>> > By comparison, here is how I resonated EAR’s antenna.  The loading coil
>> has a built-in variometer for
>> > adjusting resonance.  I put a current-transformer type RF ammeter on the
>> ground end of the coil and
>> > watched for a peak while I rotated the inner coil of the variometer.  To
>> match the final to the loading
>> > coil/variometer, I used a three turn link coil wound over the very
>> bottom turns and moved it around
>> > while watching for a dip in the final current.
>> >
>> > 73, J.B., VE3EAR
>> >
>> > LowFER Beacon "EAR"
>> > 188.830 kHz. QRSS30
>> > EN93dr
>> >
>> >
>> >
>> >
>> >
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