[Premium-Rx] Re: Ten-Tec RX-340 ??

[Chuck Hutton]

Scott:

 

What you describe sounds like the fundamental trade-offs for a PLL: 

- the wider you make the loop so that it can lock on a signal not right in
the middle of the passband (or a drifting signal), the more likely it is to
capture on an unintended signal.

            - the choice of loop bandwidth affects noise filtering.

            - the faster you want the loop to lock up, the wider the
bandwidth.

 

 

There is no right answer. A receiver dedicated to frequency hopping might
favor quick locking (wide bandwidth). My favorite implementation is a dual
bandwidth loop: it acquires lock with a wide loop and then switches to a
narrower loop once locked.

 

As for the amplitude differences between the two, I don't know why there is
a difference nor whether it really is meaningful. I have doubts as to
whether SAM means anything when the carrier is at the level of the noise.

 

Another parameter of interest is how long the loop remains on frequency when
it looses lock.

 

 

 

Chuck

 

 

  _____  

From: premium-rx-bounces at ml.skirrow.org
[mailto:premium-rx-bounces at ml.skirrow.org] On Behalf Of Ka9p at aol.com
Sent: Sunday, September 04, 2005 7:41 PM
To: premium-rx at ml.skirrow.org
Subject: [Premium-Rx] Re: Ten-Tec RX-340 ??

 

I'm really enjoying reading this thread.

Could someone maybe explain the likely basis for the difference in the SAM
performance between the HF1000A and RX-340?

After reading the string of posts, since I had the two set up in a
comparison mode on the same antennas, I wandered away from the standard SWBC
fair I usually listen to (and I still don't think the 340 SAM is bad for
that) and looked around for some weak AM stuff, and settled in on the 75
meter DX-60 net this morning.  What I found kinda surprised me.

The 340 required about 7 to 10 dbm above the noise level for SAM lock-up,
while  the WJ remained locked virtually all the time the carrier rose above
the noise. 

And as various weak AM stations came on, the WJ would take a few seconds but
lock on them when they were as much as 800 to 900 hertz high or low.  The
340 refused to lock on anything more than 300 hertz away.  The same results
were obtained on the 50 KW station on AM1000 about 1.5 miles from here. 

Is this just a difference in algorithm, or is there something in the overall
design approach/philosophy that contributes to this much difference?

And thanks for the link to the Grayland pictures  ("Honey, come look at
this, we're not so out of control here, are we ?" )

Thanks for any enlightenment, 

Scott

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