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Diamond S/RH-789 Telescopic

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hertzian

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Really? A review for a telescopic? Yes - mainly because of the 5/8 wave adjustment..

The Diamond RH789 (bnc) and SRH789 (sma) is a lightweight, good looking telescopic that can be folded at the base if necessary. It is 8 inches collapsed and 31.5 inches fully extended.

For 95-300 mhz, you adjust it to a quarter wave. For 300-1100 mhz, the adjustment is made to being a 5/8 wave. There is a black and silver sticker/chart on the bottom element in centimeters to guide you.

The bottom 8 inch section is black, as well as the bnc / sma connector. The telescoping elements are somewhat dull brushed-aluminum looking. This is a good thing! If the typical RS shiny-chrome "Adam 12" looking telescopic with loading coil puts you off, the Diamond may command a little more respect. :)

The use of 5/8 wave for above 300 mhz is interesting - there doesn't seem to be any sort of matching device for 5/8 use. Perhaps it isn't really necessary here, since we're not going to encounter much of any sort of swr loss going essentially from the antenna direct to the circuit board. 5/8 wave antennas usually have about 120 ohms resistive impedance with a large capacitive reactance that gets tuned out, but I can see why for a direct-connect whip to a scanner this may not be necessary - although purists will want a matching device.

The intent here is not to turn this into a 5/8 wave antenna thread. Tuning it to a 5/8 above 300 mhz does work.

For example, when the 789 is telescoped out to about 10.25 inches, it works much better than the canonical RH-77CA duck on 800 mhz. The 77 is not "optimized" for 800 mhz, so it is no wonder that a 5/8 wave non-impedance matched whip works better.

For that test, I used a RS Pro-106 with extended S-meter tweaks, along with the attenuator to hunt down elusive weak signal TRS systems. The telescopic performed well when adjusted to 5/8 wave.

Note that since the bottom element is 8 inches long, you really have no choice - it is too long to adjust for a 1/4 wave anyway.

Not to disrespect the RH-77CA, since I own a few, but I also tested the 5/8 wave measurement on the ungainly RS telescopic. Sure enough, even the RS telescopic adjusted to about 10.5 inches worked better than the 77CA on 800 mhz.

I won't EVEN go into gain figures, antenna patterns etc for the 5/8 wave settings. We're talking about a telescopic antenna with a circuit-board for a ground etc - this is not a fixed-position antenna, but something you can misadjust, so in this application, I'm not even going to try and claim any sort of gain figures at the 5/8 wave positions - just telescope and enjoy.
 

hertzian

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Improved 860 mhz testing!

Any telescopic extended to exactly 10 inches as measured from the BOTTOM of the bnc connector, ie the side that almost touches the radio, to the very tip of the telescopic element results in the same signal strength as the RS/GRE 800mhz duck.

This also applies to that old RS telescopic with the loading coil - just use the bottom elements only, leave the top elements pushed back down inside for a total of 10 inches, as measured from the bottom of the bnc housing.

I used the RS/GRE 800mhz duck as a reference, turned on my Pro-106 attenuator, and started to do an analysis on a TSYS of a local edacs control channel.

I got all the telescopics to reach about 2 bars signal strength after some minute adjustments - the same strength as the RS/GRE 800 duck.

It was at this point, that my other reference, a Diamond RH77CA fell out of the race. :)

It was interesting to note the slight difference in hot-spots while waving the RS/GRE 800 duck around vs the telescopics. While both were able to obtain similar signal strengths, you could tell a small difference in the pattern for the telescopics as they dropped in and out a little bit quicker. After turning off the attenuator, I could even achieve overload in certain areas.

I sincerely doubt that a matching coil for these 5/8th wave telescopics on 860mhz would make a bigger difference than the RS/GRE 800mhz duck.

So there ya' go - for 860mhz use 10 inches on a telescopic for a 5/8 wave.
 
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Fast1eddie

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I have seen those and also use a RH 77. Pitched that RS whip (although it worked well-looked too "geeky" for me) long ago. I like the measurement chart on the whip, sort of like some mil commo stuff.

Thanks for the informative review.
 

WouffHong

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RH789 Settings help needed.

I have seen those and also use a RH 77. Pitched that RS whip (although it worked well-looked too "geeky" for me) long ago. I like the measurement chart on the whip, sort of like some mil commo stuff.

Thanks for the informative review.
I have some difficulty with reading small print, even with a magnifier.

Has anyone made a printed copy of that settings guide I can get a copy of to print out?

Tnx es 73


Da Wouff/
 

WouffHong

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I have some difficulty with reading small print, even with a magnifier.

Has anyone made a printed copy of that settings guide I can get a copy of to print out?

Tnx es 73


Da Wouff/
 

hertzian

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Maybe this will help - had to put on the magnifiers to read the silver-on-black. ugh. :)

95 mhz / 82cm / 1/4 wave
120 mhz / 63cm / 1/4 wave
144 mhz / 51 cm / 1/4 wave
300 mhz / 25 cm / 1/4 wave

transition to 5/8 wave:
300 mhz / 74cm / 5/8 wave
430 mhz / 50cm / 5/8 wave
800 mhz / 27cm / 5/8 wave
900 mhz / 24cm / 5/8 wave

In practice, for FM broadcast, just extend all the way. VHF airband, collapse furthest element and so on. It's better than any duck I have as long as I'm careful with it. :)
 

jfr

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When using this on a Uniden HomePatrol, would you measure from the base of the antenna or from the hinged joint? I ask because when used with the HP, there is 4 centimeters from the base to the hinge, and it is horizontal, not vertical, as installed.

-JR
 

hertzian

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I measure from the hinge, and it seems to agree pretty well when placed on a Comet antenna analyzer and held in hand, BUT due to other variables, you don't need exact precision. Perhaps just fine-tune by ear / s-meter afterwards if you like.

Depending on which radio I put the telescopic on, fine tuning changes a little bit since the "ground" or other half of the antenna is just the circuit-board material, and your hand capacitively coupled to it. In your case it might be the case and power leads for the other half. :)

Measuring from the hinge gets me in the ballpark fastest. 50cm length from hinge to top makes a nice 144/430 mhz dual-bander. For transmitting, I'd use a remote field-strength meter, or perhaps a well-attenuated remote receiver with a decent s-meter, but for rx-only, measure from the hinge and fine-tune if you really need to.
 
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videobruce

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Sorry it's a older thread, but it's a current product.

Are there marking directly on this antenna for specific frequencies for tuning?
 

hertzian

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It is wrapped at the bottom with a decal that is bright chrome on black with measurements for either 1/4 or 5/8 wave in Centimeters.

It is very small, and hard to read in direct sunlight due to the reflective chrome. With glasses, one can manage unless you've eaten carrots all your life. :)
 
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