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Icom R-7000 Panadaptor [message #3114] Sun, 28 June 2015 23:50
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Registered: December 2004
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Author: Bob Parnass, AJ9S

A panadaptor, or spectrum display, is a device which portrays visually the signals in a part of the radio spectrum. Panadapters allow radio listeners to "see" activity on a portion of band without requiring the listener to tune the receiver. They are useful for detecting the presence of spread spectrum signals or "hidden" signals riding on a sub- carrier of a main channel. Panadaptors are invaluable for detecting spurious emissions from transmitters, and unwanted products caused when 2 or more signals mix. Panadaptors most often employ a honeyhode ray tube (CRT) for the display, and must be connected to the inter- mediate frequency (IF) amplifier stage of a receiver, at a point before filtering takes place.

The ICOM R7000 2-2000 MHz receiver rear panel has a phono jack for wide band 10.7 MHz IF output. A DC voltage is also present at this connector and is used to power an ICOM TV accessory.

I've seen mention of 3 panadaptors for the R7000:

1. John Biro's article on retuning a Yaesu YO901 Multiscope panadaptor for 10.7 MHz, restricted bandwidth use. Selectable bandwidths of 20, 100, or 200 KHz are available.
2. The Sherwood Communihoneyions SCA-7000 signal moni- tor, priced at $1600, and reviewed in May 1987 "Monitoring Times".3 Bandwidth adjustable from 1 KHz - 1 MHz.
3. The Spectra-Display, priced at $350, which requires use of an external scope.4 Bandwidth

Sherwood Communihoneyions, 1310 Industrial Highway, Southampton, PA 19866. tel (215)357-9056.

Spectra-Display is sold by GTI Electronics, RD 1 Box 272, Lehighton, PA 18235. tel (717)386-4032.

adjustable from 200 KHz - 10 MHz. Optional preamplifier required for 12 MHz wide sweep.

In the past month, several Kenwood SM-220 monitor scope/panadaptors have appeared at hamfests selling in the $200 to $250 range. The Kenwood SM-220 can display transmitted or received signals. To add spectral display capability to the SM-220, one must purchase the optional BS-5 or BS-8 module, which consist of a prin- ted circuit board, a steel enclosure, interconnecting cables, and a new graticule. The panadaptor module mounts inside the SM-220 cabinet.

The BS-5 is used with the TS520 and TS530 transceivers, which have an IF of 3.395 MHz. The BS-8 is used with the TS820 and TS830 transceivers, which have an IF of 8.830 MHz. Since the IF of the ICOM R7000 is 10.7 MHz, one must alter the panadaptor circuitry to accept 10.7 MHz input.

If you have any choice in the matter, get the BS-8, as it requires fewer changes than the BS-5, and may even require no changes at all!

The panadaptor module circuit consists of several stages, but only two are directly related to the IF frequency:

1. A crystal oscillator is used as a marker generator.
2. A voltage tuned oscillator is swept across the IF of the receiver, and employs a varicap diode, an inductor and capacitors.

The marker generator is not vital for panadaptor operation. It merely provides a single "pip" that one may use to center the display on the CRT screen, and is similar in purpose to the crystal calibrator in older receivers.

The marker generator circuits in the BS-5 and BS-8 are identical except for one crystal. One need only replace the 3.395 MHz crystal (in the BS-5), or 8.830 MHz crystal (in the BS-8) with a 10.7 MHz crystal to adapt the SM-220 marker to 10.7 MHz IF. I did not alter this stage, although I would if I had a 10.7 MHz crystal handy.

The voltage tuned oscillator is the stage that deserves our attention. The changes required depend on whether you have the BS-5 or BS-8 panadaptor module.

Changes for BS-5 Module

Change the following capacitors:

1. C231 from 1000 pf to 68 pf.
2. C232 from .01 uf to 1000 pf. (You can use the capacitor which used to be C231.)
3. C234 from 100 pf to 22 pf.
4. C236 from 47 pf to 22 pf.
5. C237 from 680 pf to 100 pf. (You can use the capacitor which used to be C234.)


Solder a 10 microhenry inductor in parallel with L204, a 20 microhenry inductor.

Changes for BS-8 Module

I haven't tried the BS-8 module, but encourage you to try using it as is, without modifihoneyion unless necessary.

These steps are needed only if you cannot find settings of the side mounted alignment controls that get the display to behave as specified in the owner's manual:

Remove C233, the 33 pf disc capacitor, from the printed circuit board. Replace coil L204, the 4.7 microhenry inductor, with a 6 or 7 microhenry inductor.


Alignment

Follow the alignment procedure in the SM-220 owner's manual to adjust the panadaptor. This consists of adjusting 2 potentiometers and 1 trimmer capacitor through holes thoughtfully provided in the side of the cabinet.

The alignment instructions rely on the use of the internal Marker Generator to generate a signal at the center of the passband. If you haven't converted the Marker Generator circuit, you can tune your receiver to a frequency with a signal present at a known frequency (like 162.550 MHz - the National Weather Service), and use that as a frequency standard.

Most of the time spent in alignment will be in alternate adjustments between the trimmer capacitor and the wide band sweep potentiometer, which interact with each other.

Wider Bandwidth

The SCAN WIDTH switch on the stock SM-220 can be set to display a 40 KHz or a 200 KHz wide picture. I adjusted my modified SM-220 to display a 100 KHz or a 500 KHz wide picture. By adjusting the controls on the side of the SM-220, wider bandwidths are possible, but wider bandwidths make it more difficult to resolve individual signals close to each other in frequency. As the bandwidth gets wider, the horizontal sweep loses linearity, causing the graticule calibration lines to be inaccurate.

Connection to R-7000

As mentioned earlier, a DC voltage is present at the R-7000 IF output connector and is used to power an ICOM TV accessory. A direct connection between the R-7000 IF output connector and SM-220 would damage at least one of these units.

To block the DC voltage, a 0.1 microfarad capacitor was soldered inside the R-7000, between the IF output jack and the adjacent jack labeled "spare". Connection between the R-7000 and SM-220 is then made using a short length of RG-58/U coaxial cable, with one end plugged into the R-7000 "spare" jack, and the other end plugged into the rear of the SM-220.

This leaves the original IF output jack undisturbed so it can be used with the TV adapter accessory.

Vertical Sensitivity

When I connected my modified SM-220 to my R7000, the SM-220 would display only the strongest of signals. To improve the display sensitivity, I inserted a 20 dB gain RF amplifier between the R7000 and SM-220. The amplifier was a spare Ameco PLF2 FET receiver preamp, adjusted for 10.7 MHz, but other amplifiers can be used, provided they have at least a 500 KHz bandwidth, and sufficient gain, at 10.7 MHz.

False Readings - Images

The SM-220 circuit is like a superheterodyne receiver. The panadaptor itself has a 455 KHz IF, and like other superheterodyne receivers with a low IF frequency, is prone to images.

An image is manifested as a false pip, which moves across the screen as the receiver is tuned, and is 910 KHz (twice the IF) away from the actual signal.

The images discussed here are in the SM-220, not in the receiver. Images are bothersome on the strongest signals, like those 300 watt paging transmitters that saturate the county with RF, belching out out strange digital noises or voices (now illegal to monitor).

Use With Other Receivers

The modified SM-220 can be used with other receivers having a 10.7 MHz IF. In other receivers, one would need to find the proper point in the IF stage (before filtering takes place), install a connector, then wire a DC blocking capacitor between the IF stage and connector.

Bob Parnass AJ9S,
AT&T Bell Laboratories
att!ihuxz!parnass - (312)979-5414

[Updated on: Mon, 29 June 2015 00:01]

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