Radio Directional Finder

[Adelie]

Originally Posted by cal40john

Is it ADF or RDF? Frenesi had an RDF. The null signal is easier to hear the minimum as opposed to tuning for the max signal. Choose your freq, rotate the antenna until you get a null, adjust the gain as necessary to get a good null, read the bearing. The antenna was marked with an arrow. An ADF you push a button and the antenna rotates until the electronics finds a null.

It is an RDF. I know to rotate the main antennae to the null, but my understanding was that the sense antennae was used somehow to resolve the 180 degree ambiguity of the main antennae. I have not found clear directions on how to use the sense antennae.

[Blue Stocking]

[QUOTE=cal40john;1369256]

Originally Posted by Adelie

I have one in the garage that will go on the boat when we buy one next year hopefully.

The only thing I don't understand about it is the sense antennae. The radio didn't come with instructions and I haven't been able to find them on-line.

I also intend to build a handheld Yagi antennae for VHF so I can radio direction find other stations or anyone that goes overboard with a handheld on their
Is it ADF or RDF? Frenesi had an RDF. The null signal is easier to hear the minimum as opposed to tuning for the max signal. Choose your freq, rotate the antenna until you get a null, adjust the gain as necessary to get a good null, read the bearing. The antenna was marked with an arrow. An ADF you push a button and the antenna rotates until the electronics finds a null.

How about after I do my bacon, eggs and fried ripe bananas for breakfast, I send you the frying pan. I'll leave the caramelized banana sugar in place.

[nigel1]

Originally Posted by Adelie

I have not found clear directions on how to use the sense antennae.

From what I remember, you rotate the loop antenna until you get a "null".
Without a sense antenna you get two "nulls", with a sense antenna, you get the one, which resolves the 180 ambiguity.
In most cases, it would not be needed, your DR position would give you a good idea of what the correct bearing should be.

[cal40john]

I remember the sense button, but never used it. I had a good idea where the station was relative to us.

[Adelie]

Originally Posted by nigel1

From what I remember, you rotate the loop antenna until you get a "null".
Without a sense antenna you get two "nulls", with a sense antenna, you get the one, which resolves the 180 ambiguity.
In most cases, it would not be needed, your DR position would give you a good idea of what the correct bearing should be.

But what's the procedure?
Align on one null, press the Sense button and if it is still a null it is the right one, or the wrong one or ...?

[nigel1]

If it works the same as the bigger sets I used on ships, the correct bearing will be when the null is still there. On the wrong bearing, the sound will be amplified.
When you come to use the set, it will be pretty obvious if you have some idea of the approximate bearing of the beacon.

[amytom]

What a timely subject. I was recently gifted the pictures RDF and was hoping someone could point me in the direction of an operators manual.

[amytom]

Another view.

[s/v Jedi]

Originally Posted by amytom

What a timely subject. I was recently gifted the pictures RDF and was hoping someone could point me in the direction of an operators manual.

Oh my. I was talking about fixed installations with the big loop antenna that you manually turned (from Sailor IIRC) or the later with double loop thatdid not need to be turned... Which was ADF I think. All the talk about portable radios, frying pans etc. is just for fun or raft survival I hope...

[Bestathook]

I have a RDF somewhere is my storage locker. As I recall it is a handsome bakelite model, even old for a RDF. Maybe even a user manual with it. Now you have me curious again, and I have to look at it again. If my mummy is found in my storage unit clutching a RDF, under an avalanche of several tons of nautical junk, it will be CF's fault!

If I recall correctly, one inventor of a RDF was Donald Crowhurst. Truth is indeed stranger than fiction, and "The Strange Last Voyage of Donald Crowhurst" is a true account of genius, sailing, electronics, insanity and philosophy, even more so than the average sailor. It is a very interesting story.

[Paul Elliott]

I used to repair the RDF receivers used in pleasure craft about 35 years ago. With the loopstick antenna you will get two sharp nulls off the antenna ends, and two broad peaks off the antenna broadsides. As I recall, switching in the sense antenna turned the broadside pattern into a cardioid (directional) pattern, which lets you resolve the 180 degree ambiguity.

These radios tuned in the AM radio band, and possibly some HF frequencies.

[delmarrey]

My RDF is now an AIS with a GPS and that's no BS.

[Jim Cate]

Well, we used RDF in the San Francisco area back in the 70's and early 80's, and my memories are that there were no "accurate fixes" as some one else has reported. But, it was better than nothing!

Also remember that they were really meant to be used with navigational buoy beacons, not broadcast stations. When the broadcast antenna is located inland, apparently various errors are introduced which further reduce the accuracy of the null. I believe that all such beacons have been discontinued, but not sure about that.

None the less, I have a vivid memory of a single-hand race from SF to Monterrey... foggy and dark, only DR for several hours... noting an AM broadcast antenna charted just inland from the city and firing up the RDF. Got a pretty good null, and just followed it on into Monterrey Bay... but being forced to listen to Gawd-awful C&W music interspersed with Bible-thumping rhetoric. It was a long night!

I sure love my GPS!

Jim

[gjordan]

Davis Instruments used to sell a hand held RDF that I used for many trips up and down the California coast. It had a reasonably good compass on it, so it served as the ships hand bearing compass also. This was pre GPS and a depth sounder, paper chart,main compass, and RDF served very well for navigation. That type of navigation required a lot of plotting, and cross checking between chart, RDF and depth sounder. I even used that same RDF to cross check my celestial when doing a night passage between islands in the Tuamotus. Yes! the Tuamotus had an airport radio beacon. An RDF is very useful, but it seems like all anyone wants to do in this day and age , is to poke a button on their multi thousand dollar DO EVERYTHING FOR YOU screen and assume it is all good. That way of doing things is great until the electrics fail, and you actually have to think. Now I must admit that when GPS became affordable , my sextant and RDF started gathering a lot of dust, but I took them on my long deliveries anyway._____ Just another opinion_____Grant.

[Cheechako]

I last used one in the mid 80's. It was handy a couple of times as my sat-nav (remember those?) seldom worked. All you really need is a small transistor radio tuned to an AM radio station in the place you are looking for. Stand in the cockpit and hold the radio in front of you extended out with your arms, rotate your body until the strongest signal is found. It actually works.