ELECRAFT KPA3 Specifiche Scaricare il pdf (Pagina 5)

From January 2009 QST © ARRL

is actually usable on CW. Alternately, you

can set operating bandwidth by setting the

high and low cut frequencies.

The receiver and transmitter performance

are top notch, as shown in Table 1 and Figures 1

through 3. There is no transceiver in the ama-

teur marketplace that has the close-in dynamic

range performance of the K3 with narrow

roofing filters installed, and most aren’t close

to the K3 in stock form. This is a result of the

HF first IF architecture of the radio, currently

shared only with the Ten-Tec Orion. This

allows the use of narrow roofing filters with

excellent shape factor, compared to radios with

the more common VHF first IF. See my sidebar

in a recent Product Review for a discussion of

the different transceiver architectures and their

impact on dynamic range.

Automatic gain control (AGC) threshold

(the signal level at which the AGC starts to

reduce gain), AGC slope and AGC hold time

are menu adjustable. I like to have the audio

level increase a bit with louder signals, but not

as much as the default provided — an easy

menu setting fixed that. Similarly, the optimum

AGC threshold depends on the ambient band

noise level, so having it adjustable is a big

plus. I set this menu item to come up with a

front panel button so I could adjust it easily

as I changed bands. Two front panel knobs

can be used for instant adjustment of menu

functions. Both a traditional noise blanker and

a DSP based one are independently available

and are effective.

Dual audio streams are provided to either

stereo headphones or stereo speaker connec-

tions. If you have the second receiver turned

on, one of the channels is connected to each

receiver. I find this the best way to operate

split frequency for working DX stations. It

currently is restricted to being on the same

band as the main receiver, but the ability

to monitor a different band is high on the

firmware to do list. A number of antenna con-

nection options allow different antennas and

front-end filters to be applied to each receiver,

if that makes sense for what you’re doing.

If you don’t have the second receiver, or it

is turned off, the two channels are still useful.

Tapping the audio effects (AFX) button brings

up a simulated stereo stream that can be a

constant phase shift between the audio chan-

nels or any of four delay intervals between the

two channels. It does add a feeling of depth

to the received audio.

The VFO tuning rate offers considerable

flexibility. The front panel RATE button

toggles the regular tuning steps between 10

and 50 Hz (20 Hz by menu selection). An-

other front panel button moves from regular

to either FINE (1 Hz per step) or COARSE.

Menu settings for COARSE steps vary per-

J. Hallas, W1ZR, “The Ten-Tec Omni-VII HF/

6 Meter Transceiver,” Product Review, QST,

Jul 2007, p 63.

There has been considerable discussion on e-mail groups about which of the

roofing filters to use to fill the five available slots in the K3. These roofing filters

are key to the radio’s superb dynamic performance, and you get to choose which

ones you want. The available filters are either five-pole (at $100 each), made by

Elecraft, or eight-pole (at $126), made for Elecraft by International Radio (Inrad).

The bandwidths available are:

 Five-pole: 200, 500, 2700 Hz.

 Eight-pole: 250, 400, 1800, 2100, 2800, 6000 and 13,000 Hz.

A 2700 Hz roofing filter is standard in both the main and subreceiver. At the

time of order the 2800 Hz filter may be substituted for $96 additional.

There are some limits to choice, however. In the main receiver, either a 2700

or 2800 Hz filter is required for CW and normal SSB transmission, the 13 kHz

FM filter is required for FM operation and the 6 kHz AM filter is required for AM or

extended (to 4 kHz) SSB transmission. The transmit filters must be in the main re-

ceiver chain. The subreceiver does not get involved in transmission, so the restric-

tions don’t apply. We selected a representative sample of filters to determine the

benefits of the narrower filters, a common question on e-mail groups.

The ARRL Lab test results are shown in Table 2. Note that we have included

some data that we don’t usually report on, because we found the results of inter-

est. First we measured the blocking and third-order dynamic range at a 1 kHz

spacing, because we felt the benefit of the narrowest filters would show up more

clearly there. Second, we generally measure from each side of center and show

the worst case reading. Here we have provided both because some of the filters

do not have a symmetrical response.

The results are interesting, and somewhat surprising — particularly the IMD

data. The blocking dynamic range, now termed blocking gain compression, acts

the way I would expect. As the filters get narrower, the close spacing dynamic

range improves rather dramatically. The 2 kHz separation data may be of most

interest to SSB contesters, while the 1 kHz data probably applies most to CW

operators. The IMD data, on the other hand does not quite act as expected —

particularly with respect to the change from 2700 to 1800 Hz filters. The dynamic

range at all spacings is actually somewhat worse with the 1800 Hz filter. It appears,

confirmed with discussions with Elecraft, that the IMD products are actually occur-

ring in the filter itself. This was observed in two samples of this filter and Elecraft

reported that they are working on developing an improved selection process.

So which should you get? For SSB, the gain compression may be most impor-

tant, so I’m glad I have the 1800 Hz in my radio. It’s worth noting that often adja-

cent channel SSB transmit IMD products will be signigicantly higher than

those generated in the receiver. I am also pleased with the 400 Hz filter in my

main receiver for tight CW conditions. Two facts are clear — even with the stan-

dard filter, this radio is a fine performer, and — better dynamic performance is

possible with sharper filters, but IMD improvement may not be as dramatic as

expected. — Joel R. Hallas, W1ZR

A Close Look at K3 Roofing Filters

Table 2

K3 Dynamic Performance with Different Rooﬁng Filters

Blocking Gain Compression, (dB) at MDS (preamp off, 14 MHz)

Spacing (kHz) Rooﬁng Filter (Hz)

above/below 2800 2700 1800 500 400

20 144/144 145/145 146/146 136/135 142/142

5 143/143 143/143 145/145 134/134 140/140

2 134/86 115/85 143/144 133/134 140/140

1 113/84 93/83 127/90 110/110 131/131

Third Order Intermodulation Dynamic Range (dB) at MDS (preamp off, 14 MHz)

Spacing (kHz) Rooﬁng Filter (Hz)

above/below 2800 2700 1800 500 400

20 104/104 105/106 101/98 104/104 105/106

5 105/103 96/106 90/84 102/101 106/105

2 99/100 90/89 74/82 90/90 106/103

1 94/81 89/79 72/81 87/82 99/99

1 2 3 4 5 6 7 8 9

Commenti su questo manuale

Nessun commento

ELECRAFT KPA3 Specifiche Pagina 5

Commenti su questo manuale

Prodotti e manuali riguardandi Ricevitore ELECRAFT KPA3