Testing Radio Antennas?

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doc540

doc540

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'61 radio has been restored and works great.

How would I go about testing the antenna to determine if it's working at optimum capacity?

Thanks
 
doc540 said:
'61 radio has been restored and works great.

How would I go about testing the antenna to determine if it's working at optimum capacity?

Thanks
Click to expand...

As far as I know there is no way of actually testing an antenna's capacity for function without specialized RF equipment.
Just hook it up and see how it does.
You can get inline amps for FM if you need more reach, but in my experience the OE antenna is pretty hard to beat unless amped for FM.
The problem with amps is it's not easy to find one that works well these days.
There is a lot of garbage out there, and if you do get one make sure you get one you can turn off separate of the radio.
A good strength signal can get garbled if over amplified, so being able to turn it off is a good thing.
 
The coax/ antenna combination is subject to extremely high impedances. To put this in perspective, a CB antenna, at 27.x mhz, is "about" 9' high for a "quarter wave." and is a "somewhat" match for 50 ohm coax

By comparison, a 550khz radio station, to be the equivalent "quarter wave" would have to be in the vicinity of 400-450 feet!!!

So your 40 some-odd INCHES whatever antenna sees extreme and complex impedances and operates "mismatched"

WHAT DOES THIS MEAN

Simply this means that BECAUSE this is such high impedance (You could not measure the standing wave, LOL) any dirt/ moisture/ other intrusion into the coax/ terminations will attenuate your signal very badly

HOW TO TEST?

Probably the simplest way is if you have access to a "megger" (high voltage leakage tester) at work, friends, etc. Otherwise, only thing you can do is test for "open" between center and ground on the coax, and continuity from ground at connector to mounting threads, and continuity from center terminal at connector to the antenna itself

(A megger is a high voltage ohmeter designed to find "breakdowns" in motor insulation, and can operate depending on model, up to 600V and more)

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The early cars had a trimmer screw, found by pulling off the tune knobs. Set the antenna length the way you intend to use. Find a weak station, use small insulated screwdriver, adjust for best reception.
 
Those ole radios, said to dial the AM band to 1400, and adjust the screw behind the knob for best reception. Thats all I know.
 
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barracudadave67 said:
Those ole radios, said to dial the AM band to 1400, and adjust the screw behind the knob for best reception. Thats all I know.
Click to expand...

I did not "used to" do it that way, here's why:

Growing up, the only decent station (we are talking 66-68) was KREM, later KJRB 790 in Spokane. This was some 60 or more air miles away. Likewise in Spokane was KXLY on 920 "less desirable"

The local station was barely worth listening to at 1400, low power switched to 250W (that's two hundred and fifty watts) at night LMAO

So instead of setting the trimmer at the "high end" I used to peak it on 790.

You ARE correct, that is the "usual way" to set the trimmer. Communications receivers in the day had the trimmer ON THE FRONT PANEL where you could get your hands on it LOL

Far bottom left, says "antenna."

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This was my "ham band" receiver when I went into the Navy in '68. You could get these cheap (I paid 50 bucks used) because they had dial drive problems, repairable with a "Jackson" ball reduction drive. They were a "hot" receiver. Trimmer is bottom right of the 4 small controls

Electrovoice_RME-4350.jpg
 
One of the best receivers I've ever owned and ever made of the vacuum tube era, and still sought after today. These did not have a trimmer, they expected you to have a high performance "matched" antenna system, that is, 50 ohms nominal

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My current radio, bought when I had some money, and also because "I thought" it would help with the locally generated RF noise problem. These are a big, expensive transciever. It has two pretty much independent receivers, which I rarely use as such

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the trimmer on a 64-65 Valiant is on the underside just behind the tuner knob, you need to access it from under the dash. Now my FM sounds like crap on my "Lexus by Pioneer" but the CD sounds fine...?
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So this being in the early A-body section, your 61 radio the trim knob is behind the radio near the antenna input. The best thing I can tell you is to tune in a strong AM station and then pull the antenna out, if the signal goes away the antenna is working.

Something else to check would be the bottom of the antenna mount for corrosion, that is the only way the mount gets grounded, you don't want any corrosion in there. Also the other thing is the antenna is "wrapped" in a metal mesh, if it is broken down at all you will get RF leakage and loose signal... or just pick up a new antenna...

If you want to have your Radio converted to AM/FM/AUX IN, PM me we can talk more.
 
Thanks, everyone.

It's an original, 1961 Dodge Lancer radio recently restored and working perfectly!

I've adjusted the trimmer to optimum reception.

Is there anything else I can do to get better reception using the original, telescoping antenna?

(perhaps the ground/connects are corroded where the cable attaches to the antenna under the fender?)

Thanks again.
 
Try these tests. Disconnect antenna lead from radio. Use Ohm meter to measure resistance from mast to center pin of cable, resistance should be only a few tenths of Ohm. Measure outer part of cable end to chassis ground, again this should be tenths of Ohms. Measure radio chassis to ground, again, tenths of Ohms. Then measure center pin to outer part, should be meg Ohms, or max on meter.
 
Whata the point to all of this? There is nothing but crap on A.M around here any more.
The classic country station is gone... No jazz... No Rock... Nothing but loudouth talk radio, holy rollers and Mexican channels.... Which are actuall the most entertaining...lol
 
KitCarlson said:
Try these tests. Disconnect antenna lead from radio. Use Ohm meter to measure resistance from mast to center pin of cable, resistance should be only a few tenths of Ohm. Measure outer part of cable end to chassis ground, again this should be tenths of Ohms. Measure radio chassis to ground, again, tenths of Ohms. Then measure center pin to outer part, should be meg Ohms, or max on meter.
Click to expand...

Thanks, that's the kind of useful information I was hoping to get.
 
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