Ground DF Normal & Alternative Techniques?

[RADIOMAN015]

During a recent actual DF mission response (12/13/2008), I placed a magnetic mount mobile antenna on the squadron van and connected the LPer (LL16) to it.  I found that this work well at determining an appropriate noise level as well when entered the search grid area whether a signal was present, without having to get out of the van (wind chills at the time were near zero).  Unfortunately, we didn't hear any signal.  On the small airport proper (7B6) with two LPer's (the old one & the new one), we basically were getting the same noise level on 121.5 & 243.0, and our ES officer (it was only him & me on the team!!!), also decided to change the LPer to the practice frequency (it was VERY cold out there!!!).  We found that we had the same noise level.  At no time were we able to lock onto a signal even after walking next to each hangar, building, &  aircraft on the small airport.

Prior to this, I've been experimenting with using my portable radio scanner (Uniden  BC296D) & Amateur Radio Portable (Yaesu FT60) (both have signal strength display).  I placed the ELT simulator on the ground floor of my home (which is surrounded on three sides by soil/ground up to the windows).  Using the BC296D scanner with a magnetic mount antenna on the vehicle, I was able to pickup the signal at 1/2 to 1 mile away from the source (initially of course as just a sound signal with no signal strength).  Of course range was determined as to what direction I was in in relation to the home's ground surround.    The FT 60, was not hooked up to the outside antenna, but was kept to my left driver's side  front window (kept within the vehicle).  Doing  basically a drive by on each street & stopping to look at the signal indicator, as well as being able to determine by speaker volume, I was able to  narrow the signal down to 6 houses (on either side of the street) without using body block technique (unfortunately, the weather got bad again, & for safety sake I terminated my exercise).

Comments on what techniques others use both with conventional DF equipment & more unconventional equipment would be appreciated!!!

RM

           

[jimmydeanno]

L-Tronics makes an antenna kit to mount to the vehicle that will point you in the direction of the ELT.  Its a two antenna system (three if you want to track 243) that feeds directly into the El-Per unit.  You can set it up in a "front to back" or "left to right" scenario and it will point you which way to go.  They work on both the old and new El-Pers.  They work great.

I've also seen Omega's used frequently as well as airband radios for body blocking. 

As for the Semiac DF unit - I can find more with tinfoil on my head.

[IceNine]

I have been using my Icom IC-A3 for years after the l-per gets me as close as possible.  A little body blocking and I'm good to go.  For those times when it is increasingly difficult (like a row of t-hangers) I just de-tune the radio by one or several freq's.

Other's use the old radio shack jetstream radios only problem with them was they were analog dials so it was difficult to get dead on the freq.

[JoeTomasone]

I tested a number of airband mag mount antennas and found that the unit from L-Tronics (NOT the two antenna system previously mentioned, but the single mag-mount antenna for $25.00) worked the best.  Ham radio antennas and scanner antennas yielded extremely poor performance in this regard.

My basic search technique is to connect the MK4 Sniffer to that antenna as I drive, listening for a signal.  With the MK4 it is very easy to tell when you've passed the source as the peak and falloff of the Sniffer's tone is painfully obvious.  So if you imagine a typical street grid, once I get the signal I will proceed on that street until I get a peak and falloff.   I then return to that point and either turn right or left - and very quickly I will be able to tell if I am headed in the wrong direction.   I just repeat this technique until I have it high enough in signal strength to proceed on foot.

On foot, I am using a 2 element beam, and with the Sniffer, well, it's usually only a few minutes until I know pretty much where the source is.


You can do much the same with an LL16 in receive mode, but it's definitely not as easy to discern the peak/falloff.   Ham radios will differ in performance based on their sensitivity on 121.5.

[Eclipse]

I use the through-the-glass scanner antenna from Radio Shack, seems to work fine.

[Stonewall]

L-Tronics makes an antenna kit to mount to the vehicle that will point you in the direction of the ELT.  Its a two antenna system (three if you want to track 243) that feeds directly into the El-Per unit.  You can set it up in a "front to back" or "left to right" scenario and it will point you which way to go.  They work on both the old and new El-Pers.  They work great.

+1 for this set-up.  Learned about this in the early 90s and bought a set for my squadron.  Used them on every DF mission and were always the first team to find it.  Never had to get out to acquire a signal and most of the time could figure out the direction from the van.

[♠SARKID♠]

L-Tronics makes an antenna kit to mount to the vehicle that will point you in the direction of the ELT.  Its a two antenna system (three if you want to track 243) that feeds directly into the El-Per unit.  You can set it up in a "front to back" or "left to right" scenario and it will point you which way to go.  They work on both the old and new El-Pers.  They work great.

+1 for this set-up.  Learned about this in the early 90s and bought a set for my squadron.  Used them on every DF mission and were always the first team to find it.  Never had to get out to acquire a signal and most of the time could figure out the direction from the van.

Thats the only antenna setup I've learned to use.  I didn't know it was common to use a single antenna.

[JoeTomasone]

I didn't know it was common to use a single antenna.

I don't know that it is, to be honest.  I've kinda gone my own way; I doubt that anyone has the same equipment and uses the same techniques that I do. 

[jimmydeanno]

Thats the only antenna setup I've learned to use.  I didn't know it was common to use a single antenna.

Our last SAREX I decided to try a single antenna setup to show the cadets on my team about signal strength.  So we mounted a single antenna on the roof of the van and I had them watch the needle on the El-Per, not look out the window, watch the needle.

As we drove by the strongest signal I wanted them to be able to recognize that and tell me to turn around if need be.  Then we'd go the other way  (X,Y axis).  I think it gave them good perspective of how it works and they could visualize the areas that they were lobbing off the search area.  It worked well because we didn't need to stop every minute to take another reading, etc.

[RADIOMAN015]

Joe & the group.  I use the ProCom CD144MBN magnetic mount antenna ($19.95, see http://www.grove-ent.com/procomm.html)  When you calculate the antenna length requirements for 121.5 mhz using
http://www.crompton.com/wa3dsp/hamradio/antcalc.html
1/2 wave is 46.2 inches & 1/4 wave is 23.1 inches.  I don't think that 3 inches in length will make that much different in signal receive!!!
I've spoken with our squadron commander and we are going to purchase the L-Tronics single antenna.  I think it is also a safety concern, especially since a lot of our DF missions have been during the hours of darkness.
I appreciate your efforts in posting your DF equipment studies.
RM

I tested a number of airband mag mount antennas and found that the unit from L-Tronics (NOT the two antenna system previously mentioned, but the single mag-mount antenna for $25.00) worked the best.  Ham radio antennas and scanner antennas yielded extremely poor performance in this regard.

[JoeTomasone]

I don't think that 3 inches in length will make that much different in signal receive!!!

You might be surprised.   During my tests I used a 2m mag mount vertical that was just shy of 20" (tuned for 146 Mhz) that was in most respect mechanically close to the L-Tronics antenna and the performance on 121.775 was noticeably inferior.