Browning MK4 or 4A receiver with no IF cage

[tubefan]

Anyone ever seen a Golden eagle MK4 or 4A receiver without an RF cage over the 6ds4 board from the factory? No cage and no holes for the cage.

[2600]

Yep. A 23-channel Mark 4.

The radio was developed as a 23-channel base. It took them so long to get the transmitter's PLL and digital channel selector design to work that it was never approved as a legal 23-channel radio. The development process for that radio took way longer than it was supposed to.

When the FCC announced the 40-channel expansion, they also decreed that no new 23-channel models would be accepted for what they called "Type Acceptance", the legal authority to sell it. Only 23-channel models that had already been approved would be legal to sell.

The Mark 4 had not yet been submitted for laboratory evaluation, the first step for Type Acceptance.

Oops. Too late.

The 23-channel approval rules were pretty loose, and Browning simply assumed the Mark 4 would pass muster and obtain that FCC Type Acceptance. This confidence led to a few of the original 23-channel Mark 4 radios being shipped as "advance samples" to their best dealers around the country.

We called these radios "escapees". 


But when the new, tighter 40-channel technical requirements were finally released by the FCC, the Mark 4 flunked horribly. Among the things that had to be redesigned was the shield over the receiver's front-end circuit board. This served to reduce the stray RF that leaked out of the receiver. Other things got changed, but that shield is the most-visible change Browning had to make.

There was no spec for receiver leakage for a 23-channel radio. None. And the Mark 4 receiver did not meet the 40-channel limits for receiver RF leakage.

Quick way to tell a Mark 4 receiver built as a 23-channel radio is the tuning dial. On a Mark 3, when you turn the dial all the way to the right, you're at the low end of the band, just below channel 1.

A 40-channel Mark 4 is the opposite way. Turn the dial to the right and you're at channel 27.

A 23-channel Mark 4 is the same as a Mark 3, with channel 1 selected turning the knob clockwise.

And if I explain why, the portion of the audience now still awake will be snoring loudly by then.

73

[tubefan]

Tune all the way to the right and I'm on 27. This was a Nichols built 4A so maybe he had a 23 chassis that he used. I have a cage. Should I drill the holes and install it or leave it as is?

[2600]

Clearly Phil knew good and well that the shield was not needed to make the radio work properly once he converted it to a 4A.

If the receiver bleeds your television while turning the receiver tuning knob, maybe that shield will help. But if it's not causing interference problems while receiving, there's no good reason to install the shield.

73