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Author Topic: remote tuner ?  (Read 16767 times)

Posts: 14455

« Reply #15 on: September 28, 2012, 12:40:36 PM »

I was actually responding to  one of his earlier posts where I thought he might have the idea that a remote tuner would reduce the touch lamp RFI issues on the lower bands.

Personally, for the amount of loss in the LMR400 run I wouldn't worry about using a remote tuner - especially if its only until spring. Only 160M and 80M are really very significant in terms of loss.


Bob  AA4PB
Garrisonville, VA

Posts: 9749


« Reply #16 on: September 28, 2012, 12:57:26 PM »

I may be way off base with this thought but , what if I put my antenna analyzer at the base of the antenna and take readings will these readings indicate what I might see with a remote antenna tuner at the base ?   Always thinking :>)  John kb2huk


The MFJ 259 series is not terribly accurate away from 50 ohms, and really most Ham type gear is not that good away from 50 ohms.  You can really come out closer with a model, short of actually measuring the antenna on a VNA.

Long feedlines below upper UHF are dominated by resistive loss in coductors, so the loss is CURRENT related. Since loss is current related we cannot really use SWR on lines that are not near a half wave long or longer. There have to be at least a few standing wave impedance cycles along the line for SWR based loss calculation to be accurate.  

You have a long transmission line, 150 feet.  SWR works fine determining loss when the feedline is long in wavelengths, so for 80 meters and up SWR values are very useful for predicting loss. On 160 SWR might not be completely useful on your 150 foot line. 160 will be terrible anyway, so why worry about it no matter what the line loss is?

Move the tuner to the antenna base, or switch in a base loading coil for 160 and 80. Do NOT expect to get away with 1500 watts on 160.

According to the eham article the loss for 150' of LMR400 feeding a 43' vertical is:

80 meters  11 dB
40 meters   2 dB
20 meters   5 dB
15 meters   5 dB
10 meters   1 dB

That's reasonable and the only bad bands 80, 15, and 20 meters. 160 will be terrible.

HOWEVER you not only lose on transmit but receive as well so on 160m, a signal would only be 1/1000th of the strength it should be if you used an antenna coupler.

First of all, we should remember the RECEIVER end of the system sets SWR on receiving. Not the antenna. On receiving the radio is the load and the antenna is the source.

More important, it takes a horrible receiver for line SWR or antenna mismatch to hinder or affect reception. A loss in efficiency or gain does not affect receiving so long as the antenna pattern does not change shape and the system limits by noise the antenna picks up. It is a common but absolute myth that improving antenna system gain always improves reception. There is usually 5-10 dB headroom for loss on upper HF, and 20 dB or more headroom on the 160 meters.

This is why 0.1% efficient antennas on 160 can hear the weakest DX on the band that can be heard at a location,  and why small loopstick antennas and whips work to get all the way into atmospheric noise on 160.

A ten meter system, because it is quieter on ten meters and there is less signal power level, might require a few percent antenna efficiency to get into propagated noise floor.  

I would not go overboard expecting to hear new signals from reducing the loss he has on the feedline on any band.  

73 Tom

Posts: 2276

« Reply #17 on: September 28, 2012, 12:59:34 PM »

Kb2huk Although as a social issue  good rapport with your neighbors is highly commendable.and wise.

The engineering and science of antenna radiation Field strength is a different matter.

The cure to RFI is when the consumer grade device has been designed to NOT pick up RF.

The FCC has recognized that fact and has required the manufacturer to either design the device to avoid RF pick up or State that the unfortunate RF pick up will be tolerated by the user of the said device. Prior to the purchase.

If you are operating your RF generating equipment properly then the burden is not yours.

socially speaking this is where technical science deviates away from social issues.

I will add that when one uses a tuner at the base of theirground mounted vertical, then the coaxial feedline will contribute very little to RFI especially when the line is routed towards the shack along the ground because it is serving as an RF transmission line being in the proper matched zone it works as it has been designed.

When the antenna is doing the radiating and transmitter harmonic suppression is properly realised The culprit/device is revealed and non hams do not like the fact.

Do not attempt to add suppression techniques to the offending device, if one chooses to do so it is advisable to include other local hams to accompany and proceed cautiously you will be held liable even if you have not really hurt anything.

There exists a rationale of: Their entitlement is greater than yours. Their telling you should stop using your ham transmitter while their electronic service is greater.or somehow takes precedent, that of course to an outside observer is obviously biased.

Having said all that staging an antenna away from one neighbor usually moves it closer to another I would center the antenna to locate equally equidistant from other homes. Then install it.

There are all kinds of reasons as to why some electronic device is doing more than being a stable light and responding to RF feild.or voltage drop.

Posts: 191

« Reply #18 on: September 28, 2012, 06:44:01 PM »

I truly appreciate all the input from you guys .  I think I will save the tuner money and go out tomorrow and try to make the antenna electrically longer put my antenna analyzer on it and make adjustments . The antenna works pretty good as is and I have been convinced to save the money and wait till next spring to work on the tower and LPA  .  thanks for your help gentleman .  John kb2huk
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