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Railfan Technology > Diamond RH77CA portable radio antenna review

Date: 07/02/22 13:11
Diamond RH77CA portable radio antenna review
Author: WW

About 30 years ago, I purchased my first Diamond RH77CA portable radio antenna.  The RH77CA has been long recommended as an antenna to improve the reception of portable amateur radios and scanners, and it has been recommended by others here often as a good antenna for railfanning radios.  Back 30 years ago, I had just purchased my first amateur portable radio and I hoped that the RH77CA would improve its reception.  I learned a valuable lesson back then that I’ve repeated here often: if you buy an antenna that will do a much better job receiving weak radio signals and you put it on a cheap radio with poor selectivity and poor unwanted signal rejection, the antenna won’t improve radio performance, it will usually make it worse.  And it did.  I sold my RH77CA with that radio because, at the time, I didn’t have any other radio that used the BNC connector mount that the RH77CA had.
Fast forward to today.  I just bought a new RH77CA to test on my Uniden BC-125AT scanner to test performance compared to the high performance Smiley Slim Duck and Laird EXH-160 series antennas (tuned to the VHF railroad channels) that I regularly use.  The reason for this, as I have noted in other posts, is that the reduced use of the VHF AAR radio channels for voice communications, precipitated by PTC implementation and FRA directives to reduce “excessive” radio traffic on the VHF railroad voice channels, has made monitoring of the UHF “train telemetry” channels much more necessary by railfans in order to determine train locations.  And therein lies the rub.  A “dual band” reception antenna will generally not perform as well as a single band antenna that is tuned to only monitor one frequency band.  But, a single band antenna will also perform less satisfactorily if it is monitoring a band for which it not designed.  So, my Slim Duck and Laird EXH-160 antennas are well-tuned to receive VHF voice railroad communications, but are not very effective for monitoring the UHF train telemetry channels. 
So, my test with the RH77CA was designed to test to see how well it would do at receiving weak signals on both VHF and UHF.  Here are the results:
Unlike the Slim Duck and the Laird EXH-160, the RH77CA is not perfectly tuned to EITHER the railroad VHF or UHF band—it is tuned to the amateur frequencies nearby to the railroad channels in the radio spectrum.
On the VHF side, the RH77CA did not perform as well as the VHF antennas specifically tuned to the railroad VHF channels, but it did pretty well.  In a 5-bar signal measurement, with no signal being 0 and a very strong signal being 5, the RH77CA signal reception strength was only one-half to one-bar less than the Slim Duck or the Laird—about the same as a “standard” stubby or regular length VHF antenna would perform.
On the UHF side, the RH77CA performed about 1 bar better than the VHF antennas.  In real world use, this is a bit more significant than it seems because the UHF train telemetry signals are weak transmissions by design, not usually receivable by even the best mobile radio antennas for more than 3-4 miles away.  So, that extra bar of signal strength might add a mile or so to the portable radio’s “hearing range” for the train telemetry channels.  Not a lot of extra range, but better than nothing.
Final thoughts—for a multi-band portable scanner or dual-band amateur radio used for railfanning, the RH77CA may be one of the best portable antenna choices out there.  That said, for VHF reception with a portable radio--nothing yet bests my perennial commercial radio choices from Icom or Kenwood, but neither comes with multi-band capability.  Also, the RH77CA is a long antenna.  I’m fairly average height, about 6’ tall, and the RH77CA mounted on the BC-125AT hanging on my belt reaches almost to my collarbone.  And, yes, the RH77CA will trounce the performance of the stock BC-125ATantenna.
Please feel free to ask questions.  I’ll do my best to answer them.


Date: 07/03/22 22:55
Re: Diamond RH77CA portable radio antenna review
Author: wa4umr

I did an experiment with the RH77CA several years ago.  I used the standard rubber duckie on my radio and I scanned all of the NWS channels.  I could get a signal on only 2 channels.  Without moving the radio, I put the RH77CA on and scanned the NWS channels again and I had signals on 5 channels.  I have to admit, I was impressed.  The NWS frequencies are real close to the railroad frequencies.  They make a good steady signal source for testing.


Date: 07/04/22 09:24
Re: Diamond RH77CA portable radio antenna review
Author: WW

I am fortunate, in a way, that the NWS channels are all some distance away from me, 40-60 air miles.  Their signals are relatively weak, so they make a good test of antenna perforrmance in the 160-170 mHz frequency range. 

As a side note, the one dual-band portable radio that I have that performs as well as the BC-125AT in receiving weak radio signals in both the VHF voice railroad band AND the UHF train telemetry railroad band is  a Wouxun KG-UV6X dual band commercial radio that I have had since around 2014.  And it performs that well with its stock antenna!  As I've noted in previous posts, I don't recommend the KG-UV6 series for railfanning for two reasons, despite my KG-UV6X's excellent reception performance:
  • I've read numerous accounts noting that the performance/longevity of the KG-UV6 series can vary quite a bit by individual radio.  I apparently got a good one.
  • The KG-UV6 series, in common with MANY Chinese radios from various manufacturers, has a serious design flaw in its scan function.  The radio keypad can not be locked while in scan mode, and the slightest bump to any key or button on the radio will knock the radio out of scan mode, often without the knowledge of the user.  In normal field use, this makes the radio essentially useless for railfanning, especially if the user is attempting to monitor both the VHFvoice channels and the 6 UHF train telemetry channels.  By contrast, the Uniden BC-125AT scanner CAN be locked in scan mode and an inadvertent key press will not knock it out of scan.    I have communicated this design defect to several vendors who have some say in the design of the Chinese radios that they sell, but, to date, the Chinese manufacturers have said that they have no plans to remedy the defect, even though a firmware revision might remedy the issue.  They are losing significant radio sales because of this--and not just in the railfan radio market, but the commercial market, as well.  Sadly, the Chinese seem better at just copy-catting other manufacturers' designs and they aren't very intutitive about actually understanding how the radios are used in real world applications. If anyone knows of any Chinese dual-band radio that does not have this scanning design defect, I would love to hear about it.  (My commercial Icom and Kenwood portable radios can also have the keypad and other buttons locked while in scan mode.)

Date: 07/04/22 13:18
Re: Diamond RH77CA portable radio antenna review
Author: Rick2582

Thank you WW for your viewpoints and reviews, excellent and on-target as usual.
I use the RH77CA on a regular basis and so do my railfriends.  For convenience it's hard to beat; it works well on VHF and UHF and changing to single band antennas with slightly better performance is not necessary for casual listening or train finding.
I do recommend careful handling in the field - dropped my radio up on Donner summit just once and the antenna broke off cleanly above the BNC connector.  The drop was only about 2 1/2 feet.  Rather disappointing, fortunately on that trip I had a spare.
Examined the break and was amazed to find the metail used is quite thin.
Never happened with a VHF or UHF Smiley Duck (I have and use both for optimum reception when needed).
So carry a spare !
Redding CA  SP milepost 258.2
KK6EL ham callsign

Date: 07/04/22 14:19
Re: Diamond RH77CA portable radio antenna review
Author: WW

Thanks, Rick5282.  Yes, the RH77CA is not as physically robust as the SlimDuck.  Very few RH77CA antennas are used in commercial applications, but a lot of SlimDucks are--the SlimDucks are built to a tougher physical standard for commercial use, as are the Laird EXH and other Laird antennas.  

Date: 07/06/22 17:56
Re: Diamond RH77CA portable radio antenna review
Author: RayH

My RH77CA has "a few" bends in it, from getting caught in the door frame as I sometimes quickly enter my vehicle and slam the door on it (during a train chase). It still works great though.

Date: 07/08/22 14:31
Re: Diamond RH77CA portable radio antenna review
Author: WW

RayH Wrote:
> My RH77CA has "a few" bends in it, from getting
> caught in the door frame as I sometimes quickly
> enter my vehicle and slam the door on it (during a
> train chase). It still works great though.

With any portable antenna, severely "kinking" the antenna can damage either the shielding and/or the wire in the antenna.  This can significantly compromise the performance of the antenna, partcularly for receiving weak signals.  If you are an amteur or commercial user that uses the radio for transmitting, such damage can also cause transmitted signal to reflect back into the radio, which can damage its electronics.  The RH77CA can be damaged fairly easily compared to the Slim Duck of Laird antennas.  The Slim Duck and Laird's weak spot for physical damage is usually where the antenna is attached the BNC (or other type) conncector.  A pretty sure sign of internal physical damage is if the "rubber" sheathing on the antenna is ripped or cracked.  

Date: 07/09/22 17:17
Re: Diamond RH77CA portable radio antenna review
Author: NiagaraMike

This antenna with my BC125AT does all I need it to do and I like the combo a lot !

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