Grid Dip Oscillators



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ALCO GDM-1... won recently on ebay... more data as available.


Ambit International The Ambit International GDO is the implementation of a design by G3WPO. Published as a kit in the November 1981 Radio Communication using two single-gate FETs. It's range was 1.6 - 215MHz, in 6 bands. It featured plug-in coils that were not tapped, in order to improve reproducibility. It was widely accepted and proved quite reliable.

Cirkit The Cirkit GDO is the updated G3WPO Mark II design. Like its predecessor, it is also a kit. There were two problems associated with the original circuit: 1) the original oscillator covered a very wide range of 135:1. This resulted in a much less-pronounced dip at the lower end of each frequency range. 2) The sensitivity of the wavemeter was not very good.

These problems were addressed by changing the two FETs to dual-gate MOSFETs (3SK88*s) which had the added capability of using a resistor in the coil to adjust gain per range. The wavemeter insensitivity was improved by changing the detector diodes to Schottky barrier types, and adding a small current to keep them in conduction.

It was determined that this circuit operated up to about 240 MHz, but that stability was difficult was difficult that high while maintaining good stability below 3 MHz. Consequently, the upper limit for this version was reduced to 170 MHz.

Other changes/improvements include: reproducible design on one pcb; new precalibrated scale; and both audio dip/wavemeter indications. This improvement was published in the April 1987 issue of Radio Communication.

B&W 600 The B&W Model 600 Dip Meter  is an AC line-powered tube-type dip meter with 5 coils from 1.75 MHz to 260 MHz in overlapping, color-coded ranges. The tube is an acorn type 955, with the 500 uA meter mounted on the side of the cabinet. Unlike several of its lesser predecessors from other manufacturers, the B&W 600 has a transformer power supply.

B&W 331-A "Little Dipper" The B&W Model 331 Dip Meter  is a battery-powered unit with 7 plug-in coil/dial combinations. Frequency coverage is from 2 MHz to 230 MHz. The '331 is unique in that it uses a bent metal-flange dial attached to the coil. Their claim is for +/- 3% accuracy. It also uses four 1.5V batteries instead of the 'standard' 9V battery. Weight of the mostly stainless-steel unit is about the same as most similarly-sized units: 1.4 lbs ( 0.6 kg). See photo and schematic below, under "Waters". Manufactured around June 1963.

Boonton 101-B w/UHF head



  • from the Triplett advertisement p.61, 1952 ARRL Handbook, 29th Ed.

The BUD Gimix is a multipurpose unit requiring no batteries, or power supply. It is calibrated for use on the 10, 15, 20, 40, and 80 Meter bands. No additional coils are needed, as the one coil does the work on all bands. It can be used as a Wave-Meter, a Monitor, a Field Strength Indicator, and a sensitive Neutralizing Instrument. Operating instructions supplied with each unit.

The former DL3QR, Helmut Ahlers,  put together a 'project' GDO, with a 'kitted run' of 50 GDOs! I was recently fortunate enough to obtain one of these beautiful GDOs. With an anodized panel, and beautiful case workmanship, this is not 'just' a homebrew GDO, but rather an instrument of superb quality. Much of this information came from the present holder of the DL3QR callsign, Frederike John-to whom I am very indebted. I have the complete unit, with coil. The photo below was provided by the seller (in Germany) Adolf Vollmer, DM2EBI.. Also, I received an email from Helmut's son Holgar. It is truly rewarding for me to have heard from him!!! His father's GDO was just terrific!

Das ehemalige DL3QR, Helmut Ahlers, fügte ein ' zusammen; project' GDO, mit einem ' kitted run' von 50 GDOs! Ich war vor kurzem genug glücklich, eins von diesen zu erreichen schönes GDOs. Mit einer anodisierten Verkleidung und schöner Fallkunstfertigkeit diese nicht ist ' just' ein homebrew GDO, aber eher ein Instrument der großartigen Qualität. Viel dieser Informationen kam vom anwesenden Halter des DL3QR Rufzeichens, John-zu dem Frederike ich sehr verschuldet sind. Ich habe die komplette Maßeinheit, mit Spule. Das folgende Foto wurde vom Verkäufer (in Deutschland) Adolf Vollmer, DM2EBI. zur Verfügung gestellt. Auch ich empfing eine eMail von Helmut' s-Sohn Holgar. Es ist wirklich befriedigend, damit ich von ihm!! gehört! Sein father' s GDO war gerade schrecklich!



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