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TK-790 and TK-890 as 2m & 70cm Radio? Do 100 Watts Matter?

9Track

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Sep 29, 2020
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I have a 45-watt Kenwood TM-V71A for a dual band 2m/70cm radio. I was wondering about the practicality of setting up a TK-790H for VHF 144-148 and a TK-890H for 440-448. This would be for 100 watts on the two bands. I'm thinking of installing an antenna around 20' high, with LMR 400 cable. Haven't settled on the exact antenna, but have been looking at some Lairds and Larsens.

I would be programming repeaters into each of them. My question is this - would I see much difference in going from 45 watts to 100 watts on VHF and UHF? I sometimes read folks saying on here, to just focus on the antenna (which I'm doing to an extent). My question would also be, why are there 100 watt radios for these frequencies if it were no different than 45 watts?

There is an HOA in my neighborhood, so I can't install a tower, or an antenna that would be visible from the street. I think it will be slightly visible, but there are a lot of trees, so think it may get kind of lost in the view.

Thanks for any advise.

Steve
 

eaf1956

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For Simplex you may have better range with 100 over 45. For repeaters not so much unless they are a great distance from you. As an example for a repeater approx 25 miles from me I can use 5 Watts with a bit of hiss or 50 with full quieting. Actually, probably full quieting with 10 but I didn't try it. The other thing being they may hear you further on simplex but can you hear them?
 

jwt873

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You'll get a little over 3dB gain.. It will be just noticeable on the receiving end.

I have a TS-2000 that puts out 100 Watts on VHF.. It has a variable power output. I keep it throttled back to 30 Watts on FM.
 

dispatch235

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Jan 27, 2005
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Dixon, Missouri
I run a TK-790 on 2 meters and use low power all the time and can hit any repeater I can hear. Simplex I use high occasionally, but my Kenwood is the 45 watt (somewhere around there) version. Had a 100 watt version for the mobile but swapped it for another lower watt version with the standard remote head. Have banks set up for amateur use, and banks for fire, ems, and law for each area around me.
The antenna setup is the key, I use Larsen for mobile and Diamond X50C that sits in the corner of my 2nd floor apt (luckily the building is all wood with vinyl siding and on a high hill)
 

mmckenna

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The 100 watt radios were really intended for getting a bit of extra range on simplex. As stated above, in ideal conditions, it'll give you 3dB of additional signal on the far end. Makes a slight difference out on the fringes of coverage. Might make a scratchy signal a bit clearer. You can get that additional 3dB by using the 100 watt radios rather than 50 watt radios, or improving your antenna system. Using higher grade coax and/or increasing antenna gain.

And then there's the marketing side of it. For people that don't understand radio, they assume that if 50 watts is good, 100 watts must be twice as good. Doubling the power doesn't give you twice the range. You would need to quadruple the power to double the range, but well before that point the curvature of the earth is probably going to get in the way. Might get you into some band openings a bit better, but that's not going to be reliable, and people can experience band openings with much less power.

With reliable repeaters and a good antenna system on your end, you won't need 100 watts to work any of them.

As for 100 watt radios, CalFire used to use them on VHF. But as they built out their repeater network, and equipment became more sensitive, they've realized they don't need that much power. They use 50 watt radios now.

The RF decks are large and heavy. If you have room for them, and the additional cost isn't an issue, you can certainly give them a try, but you'll find you can run them at lower power and do just as well. I'd not spend extra money on the 100 watt decks unless you are really serious about working simplex and are willing to put the money into better/higher antennas or directional antennas.

We are using TK-5710H radios at work in our PD cars. 100 watt VHF. They were purchased without my knowledge, and I would have had them go with the 50 watt radios. When we set the 100 watt radios up, we cranked them down to about 75 watts, just to make the finals loaf along without working hard. All the new radios I've been spec'ing for them have been 50 watt decks. They can't tell the difference.
 

tweiss3

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Keep in mind, the requirement to maintain an RF exposure evaluation is 50W on 2m.
 

MTS2000des

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Not to mention, part 97 states one must use "the minimum power necessary for communications to take place". Nothing shouts "lid" more than a guy using 100 watts or more to hit a repeater on VHF 10 miles away when they may be causing interference to others. Same goes for simplex. Getting on 52 from good elevation and belting out 100 watts into a decent antenna may make you be HEARD but if the station(s) you're trying to work are on 20-50 watt mobiles, your 790 may not hear them (at least without a pre-amp).
 

k9wkj

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where they make the cheese
I never found 100 better than 50 when on what ever base antenna I had
If this was SSB not FM then things change
I have found the 100 watts to be handy mobile, for rough terrain or distance
but even then 50 watts mostly fills the bill
I do like the big power on 6M mobile, but thats a whole different creature
 

WB9YBM

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Niles, IL
I would be programming repeaters into each of them. My question is this - would I see much difference in going from 45 watts to 100 watts on VHF and UHF? I sometimes read folks saying on here, to just focus on the antenna (which I'm doing to an extent). My question would also be, why are there 100 watt radios for these frequencies if it were no different than 45 watts?
Depends on what the station at the other end is using. For example if you're transmitting with 100 watts and the person at the other end is using only a 5-watt portable, the other person will hear you but there's a slim chance you'll be able to hear his 5 watts--too much power disparity.
 

mrweather

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Dec 19, 2002
Messages
988
I run a TK790/890 dual-band in my car (they're both dashmount 40/45 watt drawers) and I don't miss that extra 3dB. If I need more punch I'll simply switch to a higher gain antenna.

I've also run the same setup at home with a Diamond X-50 l and again, I can work everything I can hear.
 

KA7JUR

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I noticed the specifications for a TK790H show the band as 148-174 MHz (with a less common 136-156 MHz option that could be ordered on the lower power model). Although the TK790H models can be programmed down in the 144-148 range, I am curious whether readers here know if the receive sensitivity declines when used in this 2-meter range. (Does it require receiver realignment?) If the receive sensitivity does drop in the 2-meter range, this could possibly add to the difficulties of transmitting further than you can hear on simplex. On the other hand, if these radios maintain good sensitivity when on the 2-meter band, the higher power could occasionally be nice to have if you can activate it as needed.
 

mmckenna

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I noticed the specifications for a TK790H show the band as 148-174 MHz (with a less common 136-156 MHz option that could be ordered on the lower power model). Although the TK790H models can be programmed down in the 144-148 range, I am curious whether readers here know if the receive sensitivity declines when used in this 2-meter range. (Does it require receiver realignment?) If the receive sensitivity does drop in the 2-meter range, this could possibly add to the difficulties of transmitting further than you can hear on simplex. On the other hand, if these radios maintain good sensitivity when on the 2-meter band, the higher power could occasionally be nice to have if you can activate it as needed.
Depends on the individual radio. Component tolerances can throw things off and impact performance. Previous owners may have diddled with it, too.
It would be very wise to run through an alignment on it to make sure it's working as it should. Even more so if it's a used/ebay special radio.

But, to answer your question, I've not heard of anyone having any issues with doing that.
 

mrweather

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Dec 19, 2002
Messages
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I programmed my 148-174 split TK790 down to 143 MHz with no noticeable change in sensitivity.

Now, my 450-490 split TK890 required some tweaking of the VCO to get it to program down to 441 MHz. But again, I haven't noticed any change in receiver sensitivity.
 

9Track

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Sep 29, 2020
Messages
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Thanks to all for the info. I don't know if I made it clear that I was thinking about these for 100 watt base stations. I had thought about using the 100 watts for any possible repeater that was on the fringe of what I may be able to reach. Also thought that the 100 watts may be beneficial for simplex, if someone was on the fringe.

For local repeaters, I would be setting it for 45 watts. I can see the trouble if someone had an HT and was nearby and I was using 100w, but wouldn't that be an issue for any amateur base station that has a 100w transmitter? Are there different concerns for VHF/UHF than there are with HF?

Am trying to figure all of this out, hence the maybe ignorant questions. I certainly would not want to cause issues for someone on the receiving end by transmitting at too high a wattage, but wouldn't want to do that on HF, either.

Thanks again!
 

mmckenna

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For local repeaters, I would be setting it for 45 watts. I can see the trouble if someone had an HT and was nearby and I was using 100w, but wouldn't that be an issue for any amateur base station that has a 100w transmitter? Are there different concerns for VHF/UHF than there are with HF?
Yes, it would be the same issue with any ham. Difference is that most amateur radios can be set to lower power levels. The TK-x90H mobiles will only go down to around 45 watts. 45 watts is still overkill for most stuff, but I don't think anyone is going to care, unless you start running APRS on it. The APRS police guys get upset if they think you are triggering too many nodes.

With VHF/UHF as compared to HF, well, yeah, there can be a difference depending on how you look at it. Depending on where you are located, especially in a large urban area, you may find that several repeaters can share the same frequency. Running 100 watts to key up a repeater that you could hit with 5 watts may interfere with other repeaters on the same frequency. There's a few high sites I frequent where I can often here 2 or 3 repeaters on a few pairs. Keying up one often jacks up all of them. Not idea, and PL/DPL can fix that, but it can still wipe things out if multiple repeaters are within range on the same frequency.
Same goes for simplex. Taking over 146.52 with 100 watts and a high antenna may annoy some.

Am trying to figure all of this out, hence the maybe ignorant questions. I certainly would not want to cause issues for someone on the receiving end by transmitting at too high a wattage, but wouldn't want to do that on HF, either.
Absolutely not an ignorant question.
Part 97 rules say you are supposed to run the minimum power necessary to maintain communications. Since these radios will only go down to about 45 watts, and not any lower, there's not much more you can do.
 

n1das

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Feb 17, 2003
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Nashua, NH
If you are homebrewing a 2m or 70cm repeater, using one of these 100W mobiles on low power (45W) would serve as a very reliable transmitter for the repeater. I have a TK-5710H I bought "slightly used" from my dealer several years ago. The receiver does lose a little bit of sensitivity in the 2m band but is still usable. I have tried tuning it up for better sensitivity in the 2m band but to no avail. It was already as good as it gets. The RF deck is large and heavy as mmckenna said and built like a brick expletive house. It should be bulletproof reliable at 45W output when used as the transmitter in a homebrew repeater setup.
 
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