On 2013-01-16, at 10:22 AM, Wayne Willenberg wrote:
>
> Thanks to several of you who responded, I now know the larger concern
> should be the Beverage feeding my transmitted signal back into the
> receiver. This is probably of particular concern since I always use my
> linear at about 1500W when transmitting.
Hi Again Wayne,
I assume that by "...antenna input" on your transceiver, you're referring to a
RECEIVE ANTENNA ONLY jack (probably RCA-style) at the back of the rig...? (My
assumption must be correct, otherwise you're using the Beverage for BOTH
transmitting and receiving---very doubtful!).
Anyway, assuming that it's a receive antenna ONLY port that you mean, take a
close look at the schematic of your rig: I'll wager that---being a Yaesu---the
jack is automatically grounded whenever you go into transmit mode, and by
extension, you can save yourself the $$$ required that it might otherwise have
taken in purchasing an after-market grounding device for your station...
I emphasize "Yaesu" here only because I own both a Yaesu FT-980 as well as an
Icom 751A, both of which were made only a few years apart in the late 80's:
when I ran my linear with the Yaesu exciter, and using a Beverage receiving
antenna, I experienced no difficulties whatsoever---however, when I put the
751A in line with the amp & the Beverage, the transmitting envelope displayed
on my Heathkit SB-610 monitorscope was shockingly atrocious. Of course, I used
the separate receiving antenna port in each rig on both of these occasions, and
pondered the whys & wherefores of the difference...until such time as I looked
closely at the Icom schematic, & discovered to my surprise that the separate
antenna port was NOT grounded at all when in transmit mode...and that the QRO
emitted by the linear was being picked-up by the Beverage, and sent right back
into the Icom, creating untold misery with RF feedback.
It is my understanding that other Icoms exhibit this same shortcoming in their
design.
A homebrew external relay box here solved the problem for me: it utilizes a 12
VDC relay that is activated by the 751A, and which grounds the receiving
antenna whenever I transmit.
Total cost of the fix...? ZERO dollars---this is where an ample "...junque box"
(and innate stinginess!) can pay dividends, however small... Hi Hi
~73~ de Eddy VE3CUI - VE3XZ
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Topband Reflector
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