Antenna tuning with a cheap pocket radio

what antenna and what transmitter?

AM ransmitters. That's all. Transmitters and antennas may be of different types...so types (other than AM bcb) don't matter. All I need to see is when the meter reads highest v it will be there where it resonates. The antenna today is a copper pipe antenna with bottom fed loading coil. I have a circuit, but it reads very low, a radio would work better, but I'm not sure where to tap in.

What you are hoping to do, I guess, is add an S-meter to a small radio. Should be doable.

A spectrum analyzer would be good too.... maybe jury-rigged from a small-radio signal input to a computer..... peak showing on the screen....maybe into a video input?

We need more gimmicks like that for the part 15 tricks file.

I use a standard analog CB SWR meter, using the field strength function. It works close to the antenna very well if you're just looking for a peak..

I used a length of wire ~6' long that fit into the hole where the original field strength antenna was placed on the meter. Used a piece of bamboo to string the wire in the air close to the transmitting antenna. A peak was easy to see this way..

I used this circuit before, would've worked with wire, but I used an old telecoping antenna I had:

http://www.zen22142.zen.co.uk/Circuits/rf/sfsm.htm

Worked, but hard to keep up with as the readings were minimal. I had it velcro'd to a pole about 3.5 ft from the pipe. Not sure it works anymore.

Temps dropping like a rock outside, getting dark. I've got my other gear together, I'll take a shot tomorrow, if my neck strain (really hurts if I turn my head the wrong way) lets up.

Gotta watch using digital VOM's around RF. The leads will pick up RF and give false readings, especially the cheap ones. Upper tier meters have filtering to prevent this. A good 'ol analog meter is the best..

In the good old days you could measure the voltage on the AVC bus in virtually any am radio. Not so now.  Modern pocket radios use integrated circuits which may or may not have an AVC point that you can measure with a voltmeter. Schematics are typically not available.

I recommend using something like the Tecsun PL-380 (about $44 on Amazon). It has a digital display of field strength on a scale of 1 - 99. What you get for your purposes is a HIGHLY sensitive, tunable, relative field strength meter. Carl Blare has written extensively here about his experience with his similar Tecsun PL-210.

I have a PL-380. It has a huge dynamic range and will not overload even when placed almost adjacent to a transmitter antenna. To use it to tune a Part 15 transmitter, you should place it as far away from the antenna as possible while still being able to see it as you tune (probably about 5 ft). You can rotate it to almost a null position to get the reading down to a midrange value. Tune slowly to let the display stabilize each time.

You can also use it for such things as measuring your FS at long distances, seeing the FS of various broadcast stations, locating vacant frequencies, and seeing your electrical noise floor on vacant frequencies (about 25 in my area). As a bonus, you might also like having a really good LW/MW/SW/FM radio for general use.

I could swear I used to have a portable am radio as a kid that had a little analog meter on it which would assist in tuning to the peak signal of a station.. Does this ring a bell with anyone?

I googled and look on ebay vintage radios and kind find nothing like what I remember.. It may be that I'm confusing the memory with some walkie talkies or something

Yes, the TECSUN series of radios mentioned by PhilB are a must have for Part 15 radio. The corrected Model No. I have is PL-310, and it is very informative to walk near and far in the field of a Part 15 AM signal and see what it's really doing.

You can map out the actual pattern using the numbers from the read-out, and see where it is strong and where it is weak. AM signals sometimes take unexpected shapes. For example, strength can pick up along the path of overhead electric lines and go farther than elsewhere in the pattern.

Following an AM signal by car using streets may not be telling you the whole story.

Walking around on the ground with the TECSUN can reveal a whole other dimension about what your signal is doing.

Then join the ALPB.

I remember reading somewhere where a part 15 operator was tuning his transmitter for peak output while his wife was watching a S-meter of a ham receiver about a mile away. They communicated via GMRS radios. For some reason he felt this was a better way to maximize his signal.

I have one.  It's very good on SW and FM.

On mine, sensitivity is down a bit on the AM BCB -

but an external loop takes care of that.  Selectivity

is fantastic on all bands.

Anyway - I've used the "Field strength" numerical

indicator as a relative guide for RF strength. 

I know there are conversion charts to change those

numbers to other expressions of RF strength.  I've

seen the conversioin charts here on Part 15.Us - somewhere.

Anyway, it's a wonderful peice of gear, probably like

the PL-310, the PL-390, and other small Tecsun portables.

However, the "receiver with an "analog S-meter" a mile away

or so is very good.  I did that  with a guy about 25 years ago.

He was running a 160 to 190 kHz band long wave beacon.  I used

an Icom R-70.  That worked well.  Especially the analog S-meter.

Also, there are probably lots of older AM radios that could be used with

an attached external aralog S-meter.  I added that kind of meter

to a Radio Shack PRO-2005 scanner.  It worked well.  I still have it.

Bruce, DOGRADIO.

Has anyone built one of these field stregth meter kits, or have comment about them? Is it worth a $74 investment?

http://www.northcountryradio.com/Kitpages/prffsm.htm

Oh wow.. Here's one for only $28 and it's not a kit, plus their here in the states.. I realize these arn't really field stregth meters in the real sense, but certainly useful for tuning peaks, which is the quest of this thread is it not?

MFJ-801 Field Strength Meter
http://www.universal-radio.com/catalog/meters/1015.html