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Using RH77CA to transmit on ~154 MHz

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coltdude5

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Hello to all my fellow RR members. I recently starting volunteering for my county's EMA. I was given a Kenwood K-272 VHF handheld unit to use until the radio techs can install a mobile radio in my vehicle. However, I live about 13 miles away from the repeater tower and I believe the max range of the handheld with the stock antenna is only about 8 miles or so (although I know many variables can affect the range).

So I had an idea, but I'm not sure if it will work. Would it be possible to use my Diamond RH77CA antenna in place of the stock antenna to boost the range of the handheld? I have a SMA to BNC adapter that I can use to make the RH77CA fit the handheld, so that's not an issue. I'm just wondering if the RH77CA would even transmit on the frequency that I need to transmit on, which is close to 154 MHz. I know the RH77CA was designed to transmit in the 144-148 MHz and the 440 MHz bands, but I wonder if it would be able to transmit on 154 MHz and if it did, then I was wondering if the RH77CA would help to boost the range of my handheld.

I know that I could probably ask some of the employees of my county's EMA about whether my idea will work, but I'm the new guy and I don't want to appear stupid. So I figured I would join RR (which is a great site that I have enjoyed for some time) and seek the knowledge of the experts on here. My area could possibly get some severe weather tomorrow so I am hoping that someone could provide me with an answer before then. I would greatly appreciate any help that anyone could offer, even if you just have a theory about whether my idea would work. Thanks!
 

Nasby

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Yes it will work. Quite well!!! I've used mine on my commercial radio gear when I need extra range/distance and when I need to receive the weaker signals. I use it in the 155-156 mhz range.
 

mmckenna

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While not ideally tuned for 154, as he said above, it should work. The SWR would technically be off, but you will find that hand held radios are often fairly tolerant of this. With the limited ground plane they provide and the low power, they need to be.
I'd give it a try with the stock antenna first. There is no hard and fast rule about how far a hand held will transmit. Too many variables for anyone to make a blanket statement like that.
 

kny2xb

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Then will a Diamond RH77CA also be usable on 462 MHz UHF?
Or is that too far out-of-band?

I'm going to get my GMRS license so I can use my ICOM F4GT legally
[I already know that I would need the BNC-to-ICOM adapter to use the Diamond]

Just curious is all. I wouldn't mind tinkering/improving, but I wouldn't want to zap the radio doing so.

Too bad Diamond just doesn't offer a commercial version of the RH77CA.
 

mmckenna

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You'd be much better off getting an antenna that was right for the job. I've never been impressed with the ham radio antenna offerings. They are a compromise of quality to keep the prices low enough for hobbyist to buy.
If you are going to be running GMRS, then get an antenna specific to 462MHz. Actually, if you plan on running any repeaters, tune it for 465, half way between the 462 simplex & repeater output frequencies and the 467 repeater input frequencies. Using an antenna designed for 440MHz is not the best option, and not necessarily the cheapest option either.
If you want to run 70cm ham and GMRS, then you really want something with good broad bandwidth. Not a hard and fast rule, but what you will often see is that as antenna gain goes up, the bandwidth goes down. A very high gain antenna might work well over 5MHz or so before the VSWR starts to get above 2:1. If you try a low gain, say a quarter wave, you might get 20 to 30MHz of acceptable bandwidth out of it.

A commercial antenna from one of the big manufactures, like Larsen, Antennex, etc will be cheap, and from what I've seen, much more durable than a lot of the ham radio grade stuff.
 

coltdude5

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Thanks!

Thanks for the help, snjct2000 and mmckenna! I took your advice and used the RH77CA and it worked well. No one complained about my signal being difficult to hear. My RH77CA came through for me again.

I've never had any complaints about the RH77CA, even though it's designed for ham use (I have my ham ticket). As far as handheld antennas go, it has pretty good range for receiving and transmitting (on select frequencies). However, I agree it's always best to have an antenna that has technical specifications to fit one's exact needs.
 

kny2xb

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Thank You

I kind of figured that the Diamond wouldn't be usable for GMRS, but I believe that being imaginative is part of the fun of the monitoring hobby. I realize that not all ideas will pan out in the end. That's why we bounce ideas and questions off of each other.

I'm thinking of a Larsen ½ wave UHF antenna. It's the same size as a RH77CA [16"]. If they offer the ICOM connector, cool. Otherwise, I'll get the BNC-to-ICOM adapter. Plus, I could use the adapter to use a mobile antenna also.

Thank You for the input and advice.
 

mmckenna

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Larsen doesn't offer the Icom adapter. You'll have to purchase that from Icom or someone else. You'll be able to buy the antenna and mount from Larsen, but the mount will have a standard connector type on the end. Usually they are easily available with a UHF or FME. If you really search around to a good vendor, you can find N, BNC, TNC or one without the connector included. For what you want to do, I'd suggest finding one with a BNC already attached, or the FME connector with the correct BNC connector to go with it.
 

kny2xb

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I can buy the BNC-to-ICOM adapter from Universal Radio. They offer it for $18.95.

I also didn't express myself properly.

The Larsen ½ wave that I referred to is an H-T antenna, not a mobile antenna.

I meant to say that if I can purchase the H-T ½ wave with the ICOM connector already built on, I will. If not, then I will have to buy the AD-98FSC adapter, and I'll plan to have it do double duty on a mobile antenna with a BNC connector also.

Sorry for not being clearer.
 

mmckenna

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Might be worth checking with Larsen. Used to be they offered a wide range of portable antenna designs and you could order them with the right connectors for your radio. I'm not sure if they still do it, but it would be worth a look. Might be a special order thing, but I believe you could pick your 1/2 wave antenna with the Icom connector and be good to go.

If you do read the fine print on the Icom adapter, they make it pretty clear it's for testing purposes only, and not designed for long term use. Doesn't mean you can't, they are just trying to make the point that it puts extra stress on the already weak point of hand held radios, and in the long run, you may have a failure at that point.
 

nanZor

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I've put the RH77CA on MFJ and Comet antenna analyzers, and they seem to be tuned near 152 mhz for vhf, rather than being in the middle of the 2m amateur band. On uhf, both analyzers put it near the center of the 70cm uhf amateur band at around 446 mhz. I didn't add any ground planes when testing, and only used the casing of the analyzers to simulate a typical ground of a handheld. When used near the 2m amateur band, the analyzers show about a 3:1 swr ratio, which is about the max spec for some amateur HT's I've come across.
 
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