[TowerTalk] G5RV vs 40M dipole

[David Gilbert]

Certainly the SWR on the line adds loss to the system, which is why it 
can be desirable to do the matching at the antenna to avoid it. But 
doing it at the rig is typically much more flexible, is typically less 
expensive or complicated, and depending on the situation might be just 
as effective in practical terms.  As WA4LAV says, that transmission line 
loss is not always hugely significant since it depends upon the matched 
loss in the line itself (which varies with frequency and the quality of 
the line), the length of the line, and the magnitude of the SWR.  Using 
a transmission line program like TLW (available free with the ARRL 
Antenna Book) will pretty much tell you exactly what you have instead of 
you having a false sense of anything.

73,
Dave   AB7E

On 4/27/2015 9:36 AM, Tom Osborne wrote:
> One thing I have noticed with the built-in tuner on my radio is that 
> all it does is make the radio happy.
>
> The radio shows a 1:1 SWR, but the meter past the radio still shows a 
> high SWR, so if there is loss on the line, even though the radio is 
> happy, the loss is still there.  I think the tuners just give us a 
> false sense of security.  73
> Tom W7WHY
>
> On 4/26/2015 9:23 PM, Fuqua, Bill L wrote:
>>     Not everyone knows that a tuner only protects the rig. That is 
>> the job of a dummy load.
>> In fact the tuner matches the impedance of the antenna system to the 
>> rig and not only that,
>> by doing so providing the antenna with a conjugate match, that is to 
>> say the antenna's radiation
>> resistance is matched and its reactance is also matched by the equal 
>> and opposite reactance thus
>> making the antenna system resonant. If the antenna has a radiation 
>> resistance of 10 Ohms and
>> a capacitive reactance of 100 Ohms the antenna tuner matches it with 
>> 10 Ohms real resistance and
>> an inductive reactance of 100 Ohms thus providing  maximum energy 
>> transfer. While at
>> the same time it provides 50 Ohms resistive load for the transmitter.
>>    Resonating the antenna system with a tuner is equivalent 
>> resonating the antenna. The only difference
>> is that there may be some additional losses within the tuner and 
>> transmission line which are generally
>> minimal at HF frequencies. Also, there is a reduction in bandwidth of 
>> the antenna system.
>>    Yes it does change the currents and voltages in the antenna. The 
>> G5RV was an antenna developed back
>> when we had tube transmitters with a PI network output that could 
>> accommodate a broad range of
>> impedances. It also was made to work on 5 bands.
>>    Just about every AM broadcast antenna system has an antenna 
>> matching network. It is a shame that
>> they don't work.
>> 73
>> Bill wa4lav
>
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