Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang
----------------------------------------------------------------------
[EMAIL PROTECTED] wrote:
On Tue, 6 Dec 2005, Garey Barrell wrote:
You are correct. ONLY the "/CW" models have the 500 Hz crystal filter.
It is an 8 pole crystal filter (similar to the C Line filters) and so
has much sharper skirts than the L/C filter in the "B".
Hmm, so the non-CW models have a 2.4KC wide bandpass? I run my R-4B on
the .4 position which seems to be around 1KC wide which is comfortable for
me but 2.4KC would be a little wide.
Correct. The B Passband Tuner is of course an L/C filter, with fairly
wide "skirts", i.e., the passband is 400 Hz wide at -6 dB down from peak
and about 2300 Hz wide at -60 dB down. This is described as a "shape
factor" of about 1:6, the ratio of the -6 to -60 dB bandwidth. By
comparison, the 500 Hz wide crystal filter in the C Line is 500 Hz wide
at -6 dB and only 1000 Hz wide at the -60 dB point. So you can see
that nearby signals are reduced considerably more with the crystal
filters for a given distance from center of the filter. Plots of the
filter response curves are shown in the receiver manuals.
Personally, I prefer the "gentler" slope of the L/C filter because I can
hear what's going on around my frequency. Other stations opening up
nearby, calling slightly off frequency, etc. I usually operate CW with
the 2.4 kHz filter, only turning in the 1.4 k, 500 or 250 Hz wide
filters if I'm listening to a very weak station in among several much
stronger ones. But then I "grew up" with NO filters and so had to
develop the filter between my ears! :-) I can listen to several
signals at once, and choose which one I want to listen to, much as you
key in on one conversation at a party. It's a developed skill.
Anyway, unless you are planning mobile operation, or are extremely space
limited, a B or C Line would be a far superior station for CW operation.
Yep, guess i'll do that instead. I was just looking for a way to avoid
the patch cables and go with one box (and also to enjoy another new Drake
in the shack!). I run at MOST 65W drive to the L4 so the 250W PEP input
is sorta wasted.
There's not much advantage to a linear amp with the TR-4. A full KW
amp is only one S unit above the barefoot transceiver, and a 2KW only
1.5 S units above it.
One last question...
Is it normal for the T-4XB to transmit 1125Hz from the R-4B VFO frequency
when the T-4XB transceive is in RCVR mode? I would far prefer to move it
down to around 600 or 700 Hz as I don't care for the higher pitched CW
notes. When I use the R-4B as master and T-4XB transceive RCVR mode the
CW note is way up high. I would rather have it at 400hz than 1125! hi
That's a little high, but is just one more bit of evidence that
transceive is not for CW !! :-)
The reason for this is that for CW, the carrier oscillator is shifted
"about" 1 kHz from the SSB suppressed carrier frequency to move it from
the "edge" of the transmitter sideband filter passband into
approximately the "center" so the signal can get through. The B Line
is typically about 900 Hz shift. This shift is accomplished by
switching capacitor C1 (10 pF NPO) in series with the Carrier Oscillator
crystal for CW and AM. You could change this capacitor to something
smaller to reduce the offset, but obviously it has to be enough to get
the signal well into the filter passband. I think you could get it
down to 6-700 Hz, but it depends upon the particular filter in your
transmitter. You could replace C1 with a good ceramic trimmer and then
adjust the frequency lower while watching the output.
All in all, it's much better to just work "Separate" and use the SPOT
function! Then you can also move the receiver around to get the tone
you prefer and/or avoid QRM, etc.
73, Garey - K4OAH
Atlanta
Drake C-Line Service Manual
<http://www.k4oah.com>
----------------------------------------------------------------------
Submissions: [email protected]
Unsubscribe: [EMAIL PROTECTED] - unsubscribe drakelist in body
Hopelessly Lost: [EMAIL PROTECTED] - help in body of message
Zerobeat Web Page: www.zerobeat.net - sponsored by www.tlchost.net
----------------------------------------------------------------------
