RadioBanter - View Single Post

July 12th 03, 07:43 AM

In article ,
(Mark Keith) wrote:

Telamon wrote in message

I don¹t understand this kind of thinking that you should not derive the
maximum benefit of an antenna that one has gone through the trouble to
put up. Your logic of all the transformer is good for is pumping up the
S meter falls flat when you don¹t have enough signal for full quieting
or whether you can make out the program material at all if the signal is
very weak. I don¹t see the need to call anyone¹s radio lame either.

If you are using a 70 ft random wire on HF, and you don't have enough
signal level to have a usable s/n ratio on any HF freq, you would
have a lame radio. Thats just the simple facts. Nothing personal...
This is 2003. Radios are not half dead on the upper bands like to
used to be 50 years ago, unless they are toys or out of alignment.
There is no "full quieting" unless you are on FM. That would
generally be 10m up. I'll repeat it again. If you hook up your
antenna, and the background noise level increases, even if just a
little, you have all the s/n ratio you need. Increasing the signal
level beyond that point will not increase the s/n ratio. It only
pumps up the S meter. To see an improvement in copy , you would need
to use a directive antenna. Any noise along with the desired signal
has also increased in proportion, so your actual s/n ratio is the
same. Sure, the signal may sound "louder" with the higher S meter
reading, but thats mainly because the level is higher, and due to the
limitations of the filter, the signal seems "wider". But the
selectivity has slightly decreased.

The signal will not sound louder with a higher S meter reading if you
are using a radio with AGC on and it¹s working right.

Sorry to use a miss leading term ³full quieting.² I did not mean to
refer to FM modulation. Let me explain that I live in town and have
local noise to compete with any signal I pick up. This noise must be
overcome so I only hear the program material of interest. In other words
the volume can be turned up so the program material is very loud without
any background noise or hiss. Antenna efficiency that generates more
signal energy overcomes the local noise sources. You must be unusually
lucky to live in a location where all you pick up is either broadcast
signal or atmospheric noise. I don¹t think most people are as fortunate.

Most antennas output impedance is nowhere near the typical 50-ohm coax
and a transformation can remedy that.

But it doesn't matter. You don't have enough loss with the mismatch to
worry about with any decent radio. It's just not enough to knock you
out of the water. I did the math on this a few months ago, and posted
here to demonstrate this. This has been debated before many times. I
used coax feed with wild feedpoint impedances just to ensure a worst
case as far as feeder loss. It doesn't amount to enough to hurt you.
If it does, you have a lame radio. If you used a random wire direct
with no feeder, there is even less loss. For receiving, the mismatch
in that case doesn't matter enough to worry about at all.

Well OK I guess my radios are lame or busted. I must be imagining things
when signals go from ³I can just make it out S1² to ³easy to listen to
S3² on the folded dipole with the transformer. My other loop antennas
must not be working right either.

In addition there are advantages to preventing the coax interacting
with the antenna some of which you stated above.

Some antenna designs are better at rejecting local noise than
others. They only work if coupled properly to the coax resulting in
better signal to noise.

Sure, but that has nothing to do with the impedance tranformation. I
have no problems if people want to use transformers, I'm just saying
it's an option and should not really be needed as far as s/n ratio is
concerned. I don't use a tuner or matching on my wire antenna no
matter what freq I go to. I don't need to. I don't even come close to
needing it. I have plenty of signal level on any freq. Any doubt's
and you can pick a freq, and I'll record it and post as an mpeg. I
can dial up 28 mhz at 3 AM, and have plenty of background noise. If I
switch to the dummy load, all goes dead. Actually, I bet I could do
it at 150 mhz also...Sure, I can add my MFJ-989c tuner, and get a
perfect match as far as my radio is concerned, and maybe even pump up
the noise level an s unit or two. But it doesn't increase my s/n
ratio one whit. BTW, any radio can be a "lame" radio, if it's not
working right. I've had a few of mine cramp up through the years.

I¹ll see about getting my radios fixed.

--
Telamon
Ventura, California