[TowerTalk] 1 or 2 dB

[Mike Fatchett W0MU]

Dave,

You are dead on!  I have had lousy efforts worrying about stuff like 
this.  When I accept what I have up is what I have to work with and go 
for it, I always do better.  If you think you have a weak signal you 
will operate like you have a weak signal.  Think Big, Think loud and act 
like it.  It works.  The stuff between your ears can make you shine or 
drag you down.  The choice is yours.

Should be stop trying to improve?  Heck no.

W0MU

On 5/19/2022 5:24 PM, David Hachadorian wrote:
> Just knowing that you are wasting 21% of your output power in an 
> unnecessary 1 dB of feed line loss will play with your head and cause 
> you to perform sub-optimally.
>
> Dave Hachadorian, K6LL
> Yuma, AZ
>
>
> On 5/19/2022 3:01 PM, Lux, Jim wrote:
>> On 5/19/22 11:38 AM, Jim Brown wrote:
>>> On 5/19/2022 6:23 AM, Lux, Jim wrote:
>>>> I'm not so sure that it's out of reach. yes, trying to implement it 
>>>> with gear from 1980 would be challenging. But with more modern 
>>>> equipment, where the "radio" is a black box controlled by a "front 
>>>> panel" or "computer" it gets easier.
>>>
>>> The Elecraft K3 with second RX that is the same as the main RX, and 
>>> which can be synced with the main, allows diversity reception, and 
>>> I've been using it since 2008.
>>>
>>> Diversity requires an antenna for each RX, spaced as widely as 
>>> practical from each other. It was invented in the earliest days of 
>>> radio to counter the effect of selective fading, which is the the 
>>> cancellation of two or more arrivals of the wavefront from the same 
>>> TX that have followed different paths, arriving at different times. 
>>> The time differences cause the arrivals to have a variable phase 
>>> relationship with each other, combining algebraically to cancel or 
>>> add, depending on the resulting phase relationships. Diversity works 
>>> best when the antennas have the greatest spacing, so that when 
>>> cancellation is occurring at one antenna, it is less likely to do 
>>> so, or even to increase, at the other.
>>>
>>>> And the diversity combining - doing it in analog is hard, but in 
>>>> the digital domain it's much easier, and for the most part it can 
>>>> be done at audio (or post down conversion to baseband or low IF).
>>>
>>> As diversity has been practiced since the beginning, combination is 
>>> done in the brain of the operator, with audio from the two receivers 
>>> in opposing ears. That's how it's done in the K3. The result is a 
>>> sort of spatiality to the sound, a bit like the true stereo image 
>>> produced by a spaced pair of microphones dedicated to left and right 
>>> loudspeakers.
>>>
>>> Combining the outputs of the two receivers to a single (mono) 
>>> channel is problematic, because the phase relationships at audio 
>>> have a good chance of cancelling. 
>>
>>
>> For SSB, yes - a simple summing won't work.  But it's widely used in 
>> other systems where there's some processing or where the baseband 
>> phase is reliable  - For instance, on AM or FM, the instantaneous 
>> audio phase will match, so you coherently combine - typically modern 
>> diversity receive does some sort of weighting on the basis of SNR - 
>> the stronger signal gets a heavier weight, and when there's fading, 
>> it smoothly changes.
>>
>> I will say that there are *bad* implementations - I had a car radio 
>> that did diversity on FM, but the two paths were noticeably different 
>> time delay (as in milliseconds) so you could hear an apparent "echo" 
>> as it switched from one to the other.
>>
>>
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