Ponderin' on a field strength meter..
Ponderin' on a field strength meter..
I'm still designin' a ground mounted antenna that can be tuned from a distance so my fat butt doesn't mess with it while I'm doin' it! Ain't fancy but it'll work.. I think..
I don't need anything even close to accurate but I would like to be able to find a peak and a reference point to see if I'm messin' up. I used a CB field strength meter with a long piece of wire in the past but it only works close to the antenna. This is what I'm tryin' to avoid..
Neil and his loop antenna F/S indicator started me thinkin'..
What if I had a loop antenna like Neil built somewhere the R.F. field of my ground mounted antenna connected to some RG-6 runnin' back to the house and connect it to a Ramsey LPA1 amplifier at the input. Connect the output of the LPA1 to an LC circuit, somewhat resonate to my TX frequency, with a detector diode to gimmie some D.C. I figure the LPA1 might give me ~500 mW to work with. Use a 10-20 microamp meter and attenuate the output of the LC/detector circuit with a variable resistor to adjust the scale of the meter. Or, just attach a VOM instead with a couple meg load. Turn it on while tuning and off when yer done..
Comments? Ideas?
as far as I can tell. If you are going to amplify the signal then a smaller loop than I used (36" diagonal) would probably suffice. Rather than the LPA1 (no harm in trying but be wary of self oscillation) perhaps you could use a single transistor or high speed op amp as an amplifier. The RF from the loop is really strong despite the low indication I reported on the meter. The meter, though 50 uA is sensitive, still requires a lot of power to operate.
Personally, I would start with a single transistor amplifier.
If you decide to use an op amp circuit this can function both as the diode and the amplifier but you need to choose one which can handle the frequency. The spec to look for is the Unity-Gain-Bandwidth product.and it should be at least 10 mHz for this. There can be biasing problems though and this is why I recommend a single transistor.
The remote tuning function would be really nice but with my rather new outdoor antenna system it has been a "set and forget" operation. The signal drops off a little with rain but not enough to cause concern.
I think RFB mentioned that he used a loop to monitor his FS so maybe he will drop by and impart some wisdom on the subject.
Neil
Could the loop antenna be connected to the antenna input and circuit ground of your CB field strength meter? Maybe the loop will give a stronger signal so it can be used farther away.
Neil
Ain't never tried it but I betcha I'm going to.. Thanks!! (I like simple)
I had a 10' piece of wire, actually the wire antenna from the SStran kit, and taped one end to a broom stick and stuck the other end into the F/S meter. Propped the broom stick up with a plastic lawn chair.. Yeah.. Real precise, huh.. (Got Pics!)
I couldn't move it out too far because the meter movement is soo small. I had to keep it close to me. Everytime I tilted my beer, I could see the meter goin' up and down..
I'm done with all of that! 'Bout drove me insane because I'm a perfectionist when it comes to this kinda stuff. I knew when I was walkin' away it wasn't right..
Wonder if I could put my F/S meter near the xmtr/ant. and lengthen the wires that go to the meter to the house! Remove the meter from the housing and take it inside..
That should work but it will have to be kept dry.
It depends on what kind of indoor receiver you have but here I use one with an S meter and an outdoor antenna. The outdoor antenna is less subject to things moving around than an indoor antenna so the field strength reading is pretty constant.
I tapped into the S meter circuit in the receiver and brought out leads to which I connect a DVM. It gives much better resolution than the built in analog meter. Strangely, the receiver seems to need to "warm up" even though it is solid state as the signal strength indication drifts a bit for the first few minutes after power on at the receiver.
Neil
I notice that in my new Spectrum Analyzer the inbuilt tuner drifts visibly on the CRT as the unit warms up. The waveforms on screen drift by as if looking out a port hole at the passing sea.
Once it reaches "operating temperature", it stabilizes.
The Grundig AM/FM/SW port-about also drifts a lot, but a true part 15er loves to re-tune everything.