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Kenwood & EF Johnson Forum - For discussion of land mobile radio products manufactured by Kenwood or EF Johnson. For discussion of Kenwood Amateur Radio Equipment, please use the Amateur Radio Equipment forum.

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  #1 (permalink)  
Old 01-17-2018, 2:49 PM
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Default Receiver sensitivity μV question

Kenwood TK-7180H 0.25μV (wide) 0.28μV (narrow)
Kenwood TK-7360H 0.28μV (wide) 0.35μV (narrow)
Kenwood TK-760HG 0.25μV (wide) 0.33μV (narrow)


Am I correct in thinking with the above three radios the TK-7360 will not perform as well as the other two when it comes to picking up distant signals?

How big a difference will 0.03μV make?

In playing around with a TK-7180H and a TK-7360H last night, I noticed enough of a difference with my radio's to make me go check. But how much is individual radio tuning and how much is radio specification?


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Old 01-17-2018, 2:52 PM
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Not enough to notice without test equipment.
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Old 01-17-2018, 3:28 PM
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The difference is 1.4db (voltage). Not enough to make any difference.
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Old 01-17-2018, 4:10 PM
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I almost didn't try and work this one out just because info was given in microvolts.

Anyway, 0 dBm (1 mW) is .2236 V and .25 µV is -119 dBm. .28 µV is -118 dBm. So there isn't much of a difference in terms of receive sensitivity and in nearly all real world situations, it's a negligible difference. A little funny that the radios are 1.5 to 2 dB less sensitive when operated in narrowband versus wideband.
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Old 01-17-2018, 4:31 PM
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Thanks for the reply's

Kenwood specifies the receive sensitivity in μV so that's what I quoted...

I did notice a slight difference between my two radio's where receive would be clearer on a distant frequency with the 7180, but realize that could be the difference in the way they are tuned. My TK-7360 could have drifted out to be 0.34μV on wide (example, guess)
Considering it was a used radio I have no history on anything is possible...



Learning as I go,
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Old 01-22-2018, 7:30 PM
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Quote:
Originally Posted by westcoaster View Post
Kenwood TK-7180H 0.25μV (wide) 0.28μV (narrow)
Kenwood TK-7360H 0.28μV (wide) 0.35μV (narrow)
Kenwood TK-760HG 0.25μV (wide) 0.33μV (narrow)


Am I correct in thinking with the above three radios the TK-7360 will not perform as well as the other two when it comes to picking up distant signals?

How big a difference will 0.03μV make?

In playing around with a TK-7180H and a TK-7360H last night, I noticed enough of a difference with my radio's to make me go check. But how much is individual radio tuning and how much is radio specification?


Thanks,
I can tell you from experience that it's all in who tunes the radio.

I've yet to see a kenwood that didn't exceed factory specs when properly tuned.

None of my radios ever leave the bench without exceeding factory specs
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Old 01-23-2018, 12:57 AM
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It's become clear it is the one TK-7360HV radio itself that is under achieving when compared to a second TK-7360H(non V) and the TK-7180H

I just have to decide if I want my OCD to take over and run it into a radio shop to get tuned up or accept it for what it is...
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Old 01-23-2018, 1:39 AM
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Quote:
Originally Posted by westcoaster View Post
I just have to decide if I want my OCD to take over and run it into a radio shop to get tuned up or accept it for what it is...
Careful, though.
If you get the 7360HV tuned by a competent tech, it may start outperforming the 7360H.

They you'll want to take that one in and get it tuned, but make sure it's the same tech. And he's in a good mood. And he's had his coffee.

Depending on how "off" it is, you might be better off leaving it alone. If your communications needs have no tolerance for a slightly-off radio, then you have some other work to do.

But if it's really out of whack, then yeah, it's worth it. Doesn't sound like it's that far out, though.

Bench time runs around $85/hr for my local Kenwood shops.
$85 bucks might go better into upgrading your antenna, coaxial cable, or both.
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Old 01-23-2018, 1:58 AM
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It's interesting to sit down at the bench and just play. Poke a signal into a receiver and change it by 1dB, or a fraction of a microvolt. Especially a multimode receiver. You'll find that in some circumstances, a 6dB performance hit is barely noticeable, but in others, it makes the difference between not hearing something vs. perfect intelligibility.

Bottom line, perceived signal to noise ratio isn't linear, depending on mode, and relative range of the received signal level.
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Old 01-23-2018, 2:04 PM
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The use of dBm in reference to receiver sensitivity is incorrect. The correct unit would be dBV since receiver specs are usually give in microvolts. 0 dBV is equal to 1 microvolt.

Also, saying that a receiver has .35 microvolt sensitivity is meaningless. It needs (in FM) to be referenced to quieting. So, for example, a receiver would be said to have a sensitivity of .35 microvolts for 20dB quieting or 12dB SINAD etc.

There are many other issues in receiver design such a noise floors and the like which will affect sensitivity . External noises such as from a vehicle could be a major factor.
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Old 01-23-2018, 2:24 PM
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dBm is fine for stating receiver sensitivity and it would also need a reference like dB quieting or SINAD and a specified source impedance. Many commercial and military receivers are specified in dBm.
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Quote:
Originally Posted by ko6jw_2 View Post
The use of dBm in reference to receiver sensitivity is incorrect. The correct unit would be dBV since receiver specs are usually give in microvolts. 0 dBV is equal to 1 microvolt.

Also, saying that a receiver has .35 microvolt sensitivity is meaningless. It needs (in FM) to be referenced to quieting. So, for example, a receiver would be said to have a sensitivity of .35 microvolts for 20dB quieting or 12dB SINAD etc.

There are many other issues in receiver design such a noise floors and the like which will affect sensitivity . External noises such as from a vehicle could be a major factor.
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Old 01-23-2018, 3:27 PM
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Quote:
Originally Posted by ko6jw_2 View Post
The use of dBm in reference to receiver sensitivity is incorrect. The correct unit would be dBV since receiver specs are usually give in microvolts. 0 dBV is equal to 1 microvolt.

Also, saying that a receiver has .35 microvolt sensitivity is meaningless. It needs (in FM) to be referenced to quieting. So, for example, a receiver would be said to have a sensitivity of .35 microvolts for 20dB quieting or 12dB SINAD etc.

There are many other issues in receiver design such a noise floors and the like which will affect sensitivity . External noises such as from a vehicle could be a major factor.


Actually most modern receivers are being spec’d in dBm (which is referenced to 1 mW of power). The big problems with using the term microvolts are related to reference impedance and calculations. Example, many radios still in use today actually spec receiver sensitivity in μV EMF (without actually noting the value is in electromotive force) versus μV referenced to a 50Ω impedance.

Another way to look at that…0 dBm on a 50Ω impedance is 223.6 mV but it is also ~447.2 mV EMF. Either way, it’s 0 dBm because current is always constant regardless of the impedance.


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Old 01-23-2018, 11:41 PM
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Quote:
Originally Posted by mmckenna View Post
Careful, though.
If you get the 7360HV tuned by a competent tech, it may start outperforming the 7360H.

They you'll want to take that one in and get it tuned, but make sure it's the same tech. And he's in a good mood. And he's had his coffee.

Depending on how "off" it is, you might be better off leaving it alone. If your communications needs have no tolerance for a slightly-off radio, then you have some other work to do.

But if it's really out of whack, then yeah, it's worth it. Doesn't sound like it's that far out, though.

Bench time runs around $85/hr for my local Kenwood shops.
$85 bucks might go better into upgrading your antenna, coaxial cable, or both.
Very true about feeling the urge to run them all in, I believe that would be called the slippery slope...

I think our personal requirements are pretty close, except instead of an ATV I have a samurai with a camper as the "home" base. The samurai will wander off on up inactive logging roads in the mountains for some 22 miles at a time while the wife and kids stay back at camp. (or some combination of individuals...)
If it dosn't work because I have gone too far or over a mountain that's one thing, but if it dosn't work because it isn't right, well, that's just annoying...

Same antenna, same location, same power supply, consistently the V radio will show "one bar" as a receive strength with some dropout where the other radio shows "two bars" and no dropout.
One channel, I can not receive on the V radio where it does come in faint on the non V.

I think for right now it'll land up in a drawer. The 760G is still working well in the samurai.
I was horsetrading my way up to the TK7360's to take advantage of some of the new features they have.
Maybe another one will come along for the right price.... Craigslist has been pretty good to me.
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Old 01-24-2018, 12:08 AM
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I think that's a wise move. $85 into an old radio. If they find parts that need to be replaced, it can get expensive. While it's likely just an alignment issue, you never know.
If you are looking for a higher grade radio, I'd save that $85 like you suggested. Keep your eyes open for a TK-7180, NX-700 or any of the other newer VHF mobiles.

While maybe not a road you want to head down (no pun intended), the Motorola CDM series are pretty good. I've been getting them for in the $100 range. CDM-750 will give you 4 channels CDM-1250 will give you 64 or 128 depending on the exact model. The CDM-1550 will give you 160. I don't think I've ever paid more than $150 for one.
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Old 01-24-2018, 12:58 AM
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I'll call the local radio shop to see what his rates are just to know. The idea of having to plant parts into it had crossed my mind and is one of the factors behind sitting on it.
I don't have much invested in my collection at this point. I have been able to buy and sell with very little out of pocket.
There is a pretty good demand for VHF around here.
edit: Even after shop rates I'll be able to sell the 7360hv for more than I'll have in it...

On the other hand UHF dosn't move as well. Still sitting on 19 Motorola MTX4550IS radios...

Gotta confess.... After the exposure to programming the MTX4550 radio's I'm thinking I'm being spoiled by picking Kenwood to go with...
Maybe it's just what I'm familiar with but Kenwood is simply easier.

Buddy gave me a Kenwood programming cable with the DB25 serial connector on it. Still works good to program any Kenwood mobile I come across....
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Old 01-24-2018, 2:31 AM
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Quote:
Originally Posted by ko6jw_2 View Post
The use of dBm in reference to receiver sensitivity is incorrect. The correct unit would be dBV since receiver specs are usually give in microvolts. 0 dBV is equal to 1 microvolt.
DBm is indeed a valid metric for measuring receiver performance. A receiver input is more of a voltage sensitive device, as opposed to one requiring input power (base or gate of a transistor, or grid of a vacuum tube), but when the input impedance is known, dBm is perfectly fine. The beauty of using dBm is that when calculating link budgets, it's just a matter of adding the gains and losses.

Either metric, voltage or power, requires the definition of a threshold value, such as SINAD, quieting, or s/n ratio.

Yet another metric that's useful is noise figure. That's useful to know if you want to consider adding a preamp. Essential, really. If you have a receiver with a 3 DB noise figure, adding a preamp with a 4 DB NF will never help with weak signals, although it'll do a great job of making strong signals stronger.

If you know the receiver IF bandwidth, you can calculate sensitivity in uV or dBM to noise figure and back again, useful if you need to know approximate noise figure but don't have the ability to measure directly.
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Old 01-24-2018, 11:07 AM
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The current is not always constant regardless of impedance and you must know the impedance when using dBm. -120dBm into 50 ohms is a different level in uv than -120dBm into 75 ohms and so on.

To make a comparison easy lets take 1W into 50 ohms, which is 7.07107V and .14142A. Then 1W into 75 ohms which is 8.66025V and .11547A. If this was a signal generator calibrated in output voltage you can see it will take different voltage levels to reach the same power in Watts with different impedance.
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Quote:
Originally Posted by MCore25 View Post
Actually most modern receivers are being spec’d in dBm (which is referenced to 1 mW of power). The big problems with using the term microvolts are related to reference impedance and calculations. Example, many radios still in use today actually spec receiver sensitivity in μV EMF (without actually noting the value is in electromotive force) versus μV referenced to a 50Ω impedance.

Another way to look at that…0 dBm on a 50Ω impedance is 223.6 mV but it is also ~447.2 mV EMF. Either way, it’s 0 dBm because current is always constant regardless of the impedance.


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Old 02-02-2018, 12:36 AM
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So I took my $80 and found this thing.....

Won't help with the receiver sensitivity issue though...

But it does create a new problem for me.
How do I use the dang thing and interpret it's readings into meaningful information?

I need to make an adapter cable. Has a type N connector on one side and a UHF connector for the antenna on the other.

Google is my friend.
New thread with questions at some point....
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Old 02-02-2018, 1:30 AM
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Pretty good haul for $80.00.
You can easily replace the connectors on the side with the ones you desire, remove the 4 screws, pull it straight out and reinstall the connector you want.
The 5A slug is great for stock CB radios.
The 100H is good for amateur radio HF use.
The 100C is good if you are working on higher power VHF stuff, repeaters, etc.
Ideally you want to stay up near the upper end of the range of the slug, so using those on a 50 watt radio will work, but won't be as accurate.

All looks in really good shape.

Using them is pretty easy. Let us know if you want some help.
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Old 02-02-2018, 2:10 AM
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I figured I could gamble on it for that money. The reputation of the meter seems pretty good and I had no way of testing it.

The 100C has seen a lot of use. It's been twisted back and forth in the housing quite a bit. The marks on the outside of the slug are the telltale sign.
The 100H slug looks like it may have been dropped. The plastic tip is flattened/buckled a bit in the one spot (can see some dark marks in the picture where it's rubbed in the meter) and the 5A slug is the same but not as severe.

I plan on primarily using the 100C as a swr meter/antenna analyzer.

Not too sure how realistic that is, but will give it a go...
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