Topband: Two-wire switchable-direction beverage

[Michael James]

Hello Barry,

--- On Fri, 1/30/09, Barry Baker, K4CZ <k4czusa at attglobal.net> wrote:

> From: Barry Baker, K4CZ <k4czusa at attglobal.net>
> Subject: Topband: Two-wire switchable-direction beverage
> To: topband at contesting.com
> Date: Friday, January 30, 2009, 10:16 AM
> I recently built a two-wire switchable-direction beverage
> based on the
> description in ON4UN's Low-Band DXing (4th edition). 
[snip]
>  Currently, I am using two coax runs to
> the shack but will eventually use a single coax that is
> switched between the
> low impedance sides of the two transformers.
[snip]
> I followed the schematic in ON4UN's book except for two
> grounds which I omitted:
> 
> 1)   Figure 7-98A on page 7-70 shows two grounds on the far
> end of the
> beverage.  One is the ground on winding n2 of the
> transformer, which I
> included in my beverage.  However, the schematic shows a
> second ground (to
> the left of T5n1), which is connected to one of the two
> beverage conductors.
> What is the purpose of this ground?

This is a typo, and that ground should not be there. The only ground at the right (far) end of the Beverage should be on the secondary of the reflection transformer (T5a, n2).

It appears that this drawing was originally Fig. 7-23 on p. 7-22 of the 3rd edition of the same book. When it was modified for the 4th edition, there was a ground that should have been removed. I'm looking at both drawings, and it it's easy to see how such an oversight crept into the new edition. Nobody's perfect.
 
> 2)  Figure 7-98A also shows a grounded connection between
> coax J2 and coax
> J1.  What is the purpose of this ground?  Since I am using
> separate windings
> on my transformer, I don't think it makes sense to
> connect these coax
> grounds to the ground rod for T1n1.

I agree. On my new 580' 2-wire Beverage here, I'm using a single coax, and the shield is only grounded at the station end. 

I'm using a relay at the feed end of the Beverage that selects the transformer (either T1 or T4) and switches the terminating resistors across the secondaries of the transformers, rather than the primaries as is usually done. Don't think it matters.

Eventually, I may very well switch to two runs of coax, and run them both into my MFJ-1025. That'll be after we get a second Beverage up, and something to transmit on.

73,
Mike W0BTU