[R-390] Matching network

[Bob Camp]

Hi

If this list took the stand of "leave well enough alone" then 99% of 
what we do would be off limits ......

I'm only suggesting that the improvement may not be quite as much as 
you would think. A lot depends on how far off resonance the antenna is.

	Take Care!

		Bob Camp
		KB8TQ



On Aug 31, 2004, at 7:53 PM, Charles B wrote:

> Bob,
>
> So you are saying "leave well enough alone"?
>
> Chuck
>
>
> Bob Camp wrote:
>
>> Hi
>> If the purpose is general listening then a "matched" antenna may not 
>> be the best bet unless you have room to put up lots of them. If you 
>> are like most people you have limited room and the real question is 
>> how to get the most out of the antenna you have.
>> More or less a dipole is at it's minimum impedance at resonance. The 
>> magnitude of the impedance goes up as you go away from resonance.
>> If your objective is to get as much out of the antenna over as wide a 
>> band as possible then you want a higher impedance on the antenna. 
>> Simply put 120 ohms will work better than 75 and 75 will work better 
>> than 50 ohms. This holds true up to about 200 ohms or so for normal 
>> dipoles. After that point the bandwidth does not get any better.
>> This is not to say that you will get more signal out of the dipole at 
>> resonance when you load it in 120 ohms. If fact at resonance you will 
>> get a bit less. The point is that by say 20% off resonant frequency 
>> you will be even with the matched load and past that you will beat 
>> it.
>> The total difference is the square root of the ratio of the 
>> impedances so for a six db change in signal you would go from 50 ohms 
>> to 200 ohms. Even with a fairly compact antenna you should have 
>> enough to get a R-390 going below 10 MHz in the evening with either 
>> feed impedance.
>>     Take Care!
>>         Bob Camp
>>         KB8TQ
>> On Aug 31, 2004, at 4:26 PM, Charles B wrote:
>>> Hi all,
>>> what can I do to get a better match of balanced antenna (dipole) to 
>>> my R390A.  At the moment the antenna is attached to J106 and in the 
>>> same configuration as shown on 
>>> http://www.r3980a.com/html/feedpoint.html  top picture.
>>> Would an antenna tuner help such as the MFJ 959B?
>>> Chuck
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>