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Old 05-14-2018, 02:17 PM   #16
Sev
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Quote:
Originally Posted by rabbit73 View Post
IIRC, in the old preamps that had 300 ohm input there was a 4 to 1 balun inside the preamp to match the input transistor of the amp. Hard to get around it unless you use an antenna with a 75 ohm feedpoint connected to a preamp with a 75 ohm input, or use a 1/2 wave coaxial balun with an antenna that has a 300 ohm feedpoint.
Yes but you could use shielded twin lead and twist it to avoid any signal problems from the antenna and the preamp.
You would not have to worry about any additional loss caused by having to add a balun.

Any preamp that uses a balun today also has to factor in an immediate loss at the balun.
So if you had a 20db gain preamp and 2db of loss at the balun you are only getting 18db of gain.

Where as if you are using shielded twin lead you have no loss and get the full gain.

Not sure how much noise if any a balun adds to the system.
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Old 05-14-2018, 04:08 PM   #17
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All you're doing is moving the balun loss from the antenna terminals into the pre-amp's housing with those old 300 ohm input preamps.

Net gain? Zero.

Quote:
So if you had a 20db gain preamp and 2db of loss at the balun you are only getting 18db of gain.
It's probably more likely to still be 20 dB of amplifier gain but with an effective noise figure of 2 additional dB. Baluns and other such insertion losses at the input of an amp increase the noise figure which effectively reduces the sensitivity of the amp for very weak signals.
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Old 05-14-2018, 05:42 PM   #18
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Hello why is it that you sev bring up something that they don't even make no more.
And noise is why they stop making them becuse B.Tony new it was junk!!
And by the way the new antennas like the 91st has IT'S Balun built in
And your hi vhf ANTENNA do all so and the mast mount amp that I can get
Where made for the specific antennas with iT's Balun built in or not and
Is far as weak signals.go I have no problem with that uhf 145miles away
90+signal the AMP is one vhf in 10/30:dbg. I wish it had 2 vhf in with iT's 2 uhf
In at 10/45:dbg 24volts but what I did I used 2of the amp so I could stack
My 2 hi&low vhf &I did 4,91xg that I can adjust the AGL it works out of this world
Vhf I get channels 1500miles away IT'S cool how well it works on a 150Ft tower!!
and I finally ran into an old friend who did a mod on my channel master 7001
He told me that I should have no problem getting the new ATSC 03 and I do
Get a lot of low band vhf out there yes I have spent a lot of money but what
The he'll the man with the most toys before you die wins.lol Dxing is a lot of fun!!!
Good luck too everyone who else does so!!!!

Last edited by Hdb91xg; 05-14-2018 at 06:38 PM..
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Old 05-15-2018, 06:52 AM   #19
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Quote:
Originally Posted by projectsho89 View Post
All you're doing is moving the balun loss from the antenna terminals into the pre-amp's housing with those old 300 ohm input preamps.

Net gain? Zero.

It's probably more likely to still be 20 dB of amplifier gain but with an effective noise figure of 2 additional dB. Baluns and other such insertion losses at the input of an amp increase the noise figure which effectively reduces the sensitivity of the amp for very weak signals.
I had thought that perhaps since the 300 ohm to 75 ohm conversion was contained within the preamp through direct wiring it would avoid both loss and additional noise that is added by an external balun.
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Old 05-15-2018, 06:49 PM   #20
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Originally Posted by Sev View Post
I had thought that perhaps since the 300 ohm to 75 ohm conversion was contained within the preamp through direct wiring it would avoid both loss and additional noise that is added by an external balun.
We'll you thought rong!!!!
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Old 05-15-2018, 07:41 PM   #21
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Internal, external, it's the same loss. Makes no difference where it's at, it's all additive.
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Old 05-15-2018, 09:16 PM   #22
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Originally Posted by Hdb91xg View Post
We'll you thought rong!!!!
What does rong mean?
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Old 05-15-2018, 09:17 PM   #23
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Quote:
Originally Posted by projectsho89 View Post
Internal, external, it's the same loss. Makes no difference where it's at, it's all additive.
There is what I was looking for.

Thank you.
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