[Boatanchors] Re: GB> Collins R-388 vs 51J4

[jeremy-ca]

In many cases the old CATV 75 Ohm to 300 Ohm matching xfmrs will work right 
down into the BC band; it doesnt hurt to try one.
I wind my own 9:1 ferrite baluns that are flat from BC to well above 30 MHz 
and they make a big difference when using coax fed antennas.

On some BA's an extra stage of front end selectivity helps with the image 
problem of 455 KHz and similar IF's. Ive built several passive types using 
old 365-450 pf BCB caps, a multi tapped toroid and a cheap plastic switch.
Others have a tuned 2N5109 stage to improve sensitivity as well as images. 
That will be a big help as the sunspots return the higher frequencies to 
life.

Carl
KM1H



----- Original Message ----- 
From: "Garey Barrell" <k4oah at mindspring.com>
To: <glowbugs at piobaire.mines.uidaho.edu>; <Boatanchors at mailman.qth.net>
Sent: Monday, October 01, 2007 9:46 AM
Subject: [Boatanchors] Re: GB> Collins R-388 vs 51J4


> Jim -
>
> You are correct.   Both are designed to work with a high impedance whip or 
> single wire antenna.   Some use a TV receiver balun (nominally 70 to 300 
> ohms) as a step-up transformer.  Most are good all the way down to the 
> upper BC band.
>
> Actually many boatanchor receivers are happier with a Hi-Z antenna up 
> until the late 50's era and benefit from an "antenna input transformer".
>
> 73, Garey - K4OAH
> Glen Allen, VA
>
> Drake 2-B, 4-B & C-Line Service Supplement CDs
> <www.k4oah.com>
>
>
>
> N2EY at aol.com wrote:
>> In a message dated 9/30/07 9:04:40 PM Eastern Daylight Time, 
>> bluebirdtele at embarqmail.com writes:
>>
>>
>>> Are there any important differences between the Collins R-388 and the 
>>> Collins 51J4 receivers?
>>
>>
>> I don't know for sure. But I recall reading an Electric Radio article 
>> which claimed that the R-388 was designed for high-impedance antenna 
>> input, not 50 ohms. The article included modification to add low-Z link 
>> inputs.
>>
>> Never having owned either rx, I can't vouch for that, but might be worth 
>> checking out.
>>
>> 73 de Jim, N2EY
>>
>>
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