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Receiver comparison

 

After my initial troubles with a broken L2, the BITX40 is hearing well and making some surprising contacts. Here's a little comparison video of the received audio from the BITX, the FT-817, and the FT-450D.



Kent
W9WB?
 

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Kent,

I think your BitX40 had the best sounding audio of them all, the 450 next, and I was astounded at how noisy the 817s receiver was, and to think I always wanted one of those, not anymore.

Joel?
KB6QVI

On Jan 1, 2017, at 3:58 PM, Kent Vanderploeg kvanderploeg@... [BITX20] <BITX20@...> wrote:

?

After my initial troubles with a broken L2, the BITX40 is hearing well and making some surprising contacts. Here's a little comparison video of the received audio from the BITX, the FT-817, and the FT-450D.



Kent
W9WB?
 

Bitx definitely the best sounding of the lot.?

Excessive gain + AGC can create that commercial gear 'canned audio' sound that builders enjoy freedom from. ?

I'm a big fan of the FT817 but yours sounded overloaded. Did you try the attenuator and IPO??

73, Peter VK3YE
 

I did not activate the attenuator or the IPO.? I wanted it to be as apples to apples as possible. ? I can also turn down the RF gain and run up the AF gain for some of those buried signals. ? The noise is definitely there, ?but the 817 has a few extra tools to deal with it. ? I'm sure the larger speaker I'm using on the BITX helps too.?

Kent
W9WB?

On Jan 1, 2017 8:43 PM, "parkerp@... [BITX20]" <BITX20@...> wrote:
?

Bitx definitely the best sounding of the lot.?


Excessive gain + AGC can create that commercial gear 'canned audio' sound that builders enjoy freedom from. ?

I'm a big fan of the FT817 but yours sounded overloaded. Did you try the attenuator and IPO??

73, Peter VK3YE
 

to bat for thr ft817nd, its big compromise is the speaker itself. a larger speaker helps. my main complain about it is the rx current consumption

On 02-Jan-2017 8:23 am, "Kent Vanderploeg kvanderploeg@... [BITX20]" <BITX20@...> wrote:
?

I did not activate the attenuator or the IPO.? I wanted it to be as apples to apples as possible. ? I can also turn down the RF gain and run up the AF gain for some of those buried signals. ? The noise is definitely there, ?but the 817 has a few extra tools to deal with it. ? I'm sure the larger speaker I'm using on the BITX helps too.?

Kent
W9WB?

On Jan 1, 2017 8:43 PM, "parkerp@... [BITX20]" <BITX20@...> wrote:
?

Bitx definitely the best sounding of the lot.?


Excessive gain + AGC can create that commercial gear 'canned audio' sound that builders enjoy freedom from. ?

I'm a big fan of the FT817 but yours sounded overloaded. Did you try the attenuator and IPO??

73, Peter VK3YE
 

Having a passing familiarity with the inner-workings of the FT-817, one of the problems with it is that its AGC is not well-designed.

Unlike most AGCs, the time constant appears to be different for weak signals (<S9) than above, but this has to do with the unfortunate "volts/dB" curve of the AGC control voltage: For weaker signals, it is reasonable, but for strong signals a small change in voltage = more dB. The net effect of this is that the AGC seems to be inconsistent in the manner described.

When I use my FT-817 - particularly on a busy or noisy band - I make use of the attenuator to keep the S-meter in the "lower half" (<S9). In this way, one avoids the de-facto audio compression that seems to occur when the AGC is in its upper range where the time constant - even on "slow" - is faster than what one would ever choose intentionally.

Interestingly, I've not see this AGC problem discussed much as its cause isn't immediately obvious and I have not ever seen any attempted fixes but it does explain the sometimes "heavy" sound attributed to this radio. If nothing else it can serve as a cautionary tale to someone designing their own AGC loop.

73,

Clint
KA7OEI

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