I just got a 2 meter transciver a few weeks ago. Its a Kenwood TR-7400A I thought it would be fun to have some local contacts.

I hooked it up to my 20 meter inverted V dipole that I have on my roof, just too see if I could hear anything. I could hear the local 2 meter net come in pretty good sunday night. Even made a weak contact using the 20 meter antenna.

Well, I built a 2 meter J pole antenna. This one is the plan I used, but there seem to be about a hundred that all look very much alike.
http://www.n7qvc.com/copper.html

I finished it tonight, and I hooked it up inside, standing in a corner, and the results were pathetic. With the 20 meter dipole, I could get the output meter to read about a 6, with the 2 meter antenna, less then a 2! I tried moving the feedpoints, with no real change. I don't have a SWR meter for the 2 meter band, so I am just using the "output" meter and what I hear being recived to gauge my success (or lack of ) The manual says the meter should read around a 9 with a good match.

I'm hoping a fellow ham can answer a few questions so I can maybe understand this all better.

Can I even expect this antenna to work at all inside a house? I know outside is always better, but I thought it would work better inside then a completly wrong antenna outside.

If I have the 2 meter antenna and a 20 meter antenna both outside at about the same hight, should the 2 meter greatly out preform the 20 meter for receiving? Our is most of the differance going to be noticed when I transmit?

Why do some of the 2 meter J pole designs have the center of the coax on the long element and the braid on the short element, and some are the other way around? Does it matter? I have tried both ways.

I have some other questions too, but I'll wait and see if someone can help me first

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The 20m dipole will not work well at 2metres.

Get yourself an SWR meter that works at 145Mhz, using the transciever output meter is a recipe for failure and burnt out PA transistors in your 7400.

GM3ZMA

The correct antenna will always work better, and outside will always be better than inside, for a given height.
What are you using for coax and how long is it? The losses in a coax cable can be significant at 145Mhz.

I have no idea, I have never built or studied this antenna.

OK, lets hear them.

JimB

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Thank you for the reply, Jim. I do appreciate it.

I am using about 25 feet of 50 ohm coax to feed the J pole.

I do want to get a VHF SWR meter, or possibly build one.

I found this circuit.
http://www.scribd.com/doc/267448/Poc...-VHF-SWR-Meter

I've never built one before though. I don't quite understand the 50hm: stripline.

Most of the other questions I have are related to the J pole antenna and how it works. Maybe I will ask about it on the eham.com boards. Maybe sombody uses the same one.

Are you very active on the air waves? What bands do you work? I have mostly dabbled in 20 meters since I got my general ticket this spring.

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Buy one, they cost very little (G8MMV)

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Yes but what sort of coax?
Is it good quality new stuff or something which has been laying around for a while?

A good idea, but if you want to build your own, you really need a good 50ohm load to use when setting up the SWR meter.
Nigels suggestion of buying one is a good idea, modest ones are not expensive and will save you a lot of grief if you dont have the equipment to set up a home made one.

Using the stripline is a good idea, but a bit fussy for a beginner project.
I also think that he has spoilt the thing by using a bargraph display, a proper moving coil meter would be much better to use.


You could try asking on QRZ.COM, but one or two of them on there can be a bit viscious sometimes.

Not as active as I would like to be, I listen a bit on 40 and 60metres, but very rarely do I put the microphone where my mouth is, so to speak

JimB

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Hi Andy
Your 20m inverted V is up fairly high and there is a lot of wire up there for a two meter antenna, so it would tend to look like something approaching a longwire antenna. This means that it will actually work pretty well as a receiving antenna but only in specific directions and maybe not so well in other directions. Antennas like this will have many sharp lobes of radiation rather than one big circle or donut like we see with dipoles and monopoles. For transmitting, we always worry about the impedance match at the radio since a really bad match can cause overheating and even damage in extreme cases. Many radios have protection circuits that will automatically back off the transmitter power when a bad impedance match is seen by the transmitter. I am guessing that the impedance match of your 20m antenna at 2 m may be only fair, like it might well be 3:1 or 4:1 VSWR. This is actually not a disaster because some cellphones settle for VSWRs this high ( but probably not the better ones), and you will get decent receiver performance at these kinds of VSWR. Unfortunately, many transmitters start to back off their power at VSWRs of 2:1 or less. Another thing worth mentioning is that long runs of thin coax cable will make your VSWR look better too, but that is because you are burning power up in the cable and not the antenna which is wasteful and degrades your on-air signal strength. A 25 foot run of coax isn't all that much so I would think that even regular RG58, the most common type of 50 ohm cable, is probably good enough for now. Theoretically, decent quality RG58 should only attenuate your signal by 1.4 dB which is not much, but poor quality coax can be worse, maybe double that. Even so, this would not explain noticeably poor performance of a new antenna.


In the VHF/ UHF world, antenna height is everything. I would guess that your jpole might be 10 dB worse than it could be just because its not up above the house. If you can get it up as high as 35 or 40 feet it will work well. As others have mentioned, you need to measure your VSWR with a meter to really get a feel for whats going on. If you get the VSWR below 2:1 at the radio, and your coax is not faulty (like has a nail through it or something like that), and your antenna is up on the roof or higher, then things will work well.

VE7COR

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RadioRon

 

Well, over the weekend I had a chance to half-ass get the antenna onto the roof of my porch. (the neighbors must think i'm nuts!)

I got a huge improvment in preformance. I still don't have an SWR meter, so I don't know how much I am putting out, but it receives alot better and the power meter on the 7400 comes up to around 7 or 8 on the higher end of the band.

I haven't been ablr to make any contacts yet though. kinda surprises me.

Since you guys have been so nice to humor me, i'm gonna throw this out there. I am confused on the concept of the PL tones to access repeaters.

The 7400a has optional tone boards that can be added for tone burst. I didn't get one with my radio. The local repeaters all seem to use differn't tones.

The one I want to get into says it uses a 136.5 Hz tone. The manual for the tr-7400a shows the tone burst oscillator moduals ranging from 1800 Hz to 2550 Hz. It also has a tone squelch CTCS mode with filter modual freqs. ranging from 88.5 Hz to 156.7 Hz, with my 136.5 Hz also listed. I'm confused on what I actually am after here

Does anyone here know if it is possible to build a add on tone board that would plug into the radio and allow me to change the tone easier then having to open the radio and change moduals? I have googled with no luck yet.

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Years ago we used to add tone burst boards to 2m rigs, they were usually built using a simple 4001/4011 CMOS gate (or something like that) - as far as I'm aware all UK repeaters require the same tone burst, 1750Hz for 600mS?.

It would seem rather stupid to require different ones?, and anything remotely 'modern' would have it built-in.

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Anyone engaging in a technical hobby will be regarded as weird by the non-technical masses around him.

Many antennas are greatly influenced by their surroundings, looks like this antenna is working properly now it is "in the clear".

That all depends on what you have done to try and make contacts!

I think that radio is quite old now, it was probably never fitted with one from new.

The tones are to prevent a distant station which is using another repeater on the same frequency, from "opening" your local repeater.

Many years ago, amateur repeaters just required a tone burst at the beginning of the users transmission to open the repeater.
In the UK and Europe, the tone was 1750hz for 300mS. Other areas such as USA and Japan may have been different.

It is now customary to have a continuous sub-audible tone (eg 136.5hz) on the users transmission to open the repeater.
OK 136hz is not exactly sub-audible, but the level of the tone is quite low and is not usually noticable.

Yes it is possible to build a tone generator. You will need a frequency counter to set it up though.

JimB

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Yeah, it is certinly working now, but its sitting outside a window on a lower part of my roof. I am thinking the house is probably blocking 180 degrees of its radiation to some degree anyway, as its only a few feet from the house. But atleast its working! As soon as the ice melts, i'll get it up higher and in a clear spot.

Alot of calling CQ on simplex freqs. 146.52 MHz is supposed to be the national calling frequency in the US as far as I can tell, but I have not made a contact on it yet. Maybe everyone just hangs out on the repeater output frequencys nowadays? Maybe I am only getting out a few miles for all I know. I'm so new to 2 meter I don't know.
Sunday night the local radio club meets on 2 meter, but its on a repeater, so I can't check in since I don't have the tone capability. Seems like it would be kinda rude to shout simplex at them.

It was an option. It talks about 2 different moduals in the manual, that were avalible in a bunch of freqs. I'll try and remember to post that page of the manual tonight when i get home.

Have you seen any scematics or anything online for doing this? I thought it would be pretty common, but I haven't dug up much yet. I'm willing to invest in a frequency counter, so thats not a problem.

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I don't know if it helps any, but here are the 2 pages that talk about the tone in the TR-7400 manual. Kinda hard to read, but easier then me trying to expalin it

Here is the local radio club site with the repeater info. http://www.marcmvra.net/
one repeater says 100 Hz and the backup says 136.5Hz. They have been using the backup the last few nets.

Bottom line is I need somone to help me understand what I need to do with the TR-7400 to access these. What mode should it even be in? The 4 modes are described in the manual pages I posted.

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I think you need to transmit with a sub-audible tone with your transmit audio in order to cause the repeater to work. This tone is sent for the entire time that you have keyed your radio. Sub-audible follows a standard called CTCSS and some companies made up their own names, like Motorola made up the name PL or Private Line, they are all the same thing. The club says you need to send 100 Hz CTCSS tone when you transmit to the repeater. Don't worry about how that sounds at the other end, because any receiver designed to accept CTCSS tones also includes a filter to take the tone out of the received audio so that nobody hears it.

In your radio you need a CTCSS tone board that can generate the 100 Hz. The manual mentions the original option board having a SUB mode, and this would be the correct mode to choose. Unfortunately, that old option board only allows one tone to be used which is no longer viable. You need to be able to select different tones for different repeaters, so it would be better to fit a more up to date tone board into your radio. There are some popular suppliers that make boards to fit your radio. Here is one link that I just found:
http://www.com-spec.com/insheet/tr7400a.pdf

this company is Communications Specialists www.com-spec.com and is mentioned a lot in ham conversations about adding tone boards.

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RadioRon

 

Thanks Ron! I'm glad to know there is a ready made option. Not even that bad of a price (around 30 bucks).

I'd kinda like to build one though.

I found this
http://www.ramseyelectronics.com/dow...anuals/QT1.pdf

Can't seem to find the kit on the site, but the PDF has the parts list and PCB artwork. Being as its so simple, I think I can follow it well enough to make one on stripboard.

I can't find the IC though! MX165CP Datasheet:http://www.datasheetcatalog.com/data...6/MX165C.shtml

You wouldn't happen to know where I could get 1 or 2 of these would you? Or if there is somthing it cross referances to?

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That IC is a fairly old model and has been discontinued from the manufacturer. You can either keep looking around for a specialty supplier that might have one in stock (there are online sellers of unusual and old ICs), or you can modify the circuit to accept the latest chip that does the same functions. The chip used to be made by MX-COM but the company was bought by (or evolved somehow into) CML Microcircuits quite a few years ago. Here's the CML site with the latest ICs
http://www.cmlmicro.com/Products/Index.htm
Click a selection under "Two Way Radio" "signalling" "CTCSS" to see the parts available and choose from the part numbers on the left. Looks like FX335 might be a good choice. The problem you might run into is that there aren't very many distributors for this makers ICs. Check out the "Distribution" pulldown.

There aren't very many companies making standalone CTCSS encoder/decoder ICs and MX-Com has been the most prominant in the ham radio world, so I don't have any other makers to suggest at the moment. In brand new radios the CTCSS functions are often embedded into the controller or more complex audio processor IC so you don't often see a chip just for CTCSS in the new radios.

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RadioRon

 

Thanks Ron for filling me in on the age of that IC. No wonder I haven't found it anyplace. I guess I don't really even want to use it now, seeing as its just going to get harder to find if I need to replace it in the future.

I emailed the Minneapolis distributor of the FX335 to see if they can offer any assistance in obtaining a few. Worth a try I guess.

I realize CTCSS is built into modern rigs, but i'm still a little surprised it dosn't seem to be more of a common thing to add it to an older rig. Isn't that part of what ham radio is all about? Building stuff yourself?

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