Topband: RIG PROTECTION FROM BEVERAGES

[Eddy Swynar]

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